Introduction to Robotics

Robotic systems represent in principle new technical means of complex automation production process. Handwork can be totally eliminated by their use, both in basic and auxiliary technological operations.

Kinematic modelling of manipulators plays an important role in contemporary robot control. It describes the relationship between robot end-effector position and orientation in space and manipulator joint angles. It also describes the correlation between linear and angular velocities of the end-effector and joint velocities. Since kinematic modelling is an inevitable step in modern robot control, in this chapter we will consider the main principles of manipulator kinematic model generation.

The modern development of robotic mechanisms is rapidly increasing. A linear composite speed of manipulation robots now achieves 5 m/s and angular speed of their particular links (segments) surpasses 8 rad/s. This is not only characteristic of robots with small reachability, but also of robots with larger manipulator possibilities. Such an increase leads to a significant dynamic effect in robot mechanisms, necessitating a careful study of their dynamics. Adequate dynamic models of manipulation robots can be used for robot mechanism design, optimal choice of its actuators, and also for modern robot controller design. A mathematical model derivation of the dynamics of artropoidal robot configuration, frequently used today in industrial practice, is presented below.

In this chapter we shall consider the problems concerning control synthesis for manipulation robots. The control system represents a very important part of the robotic system. Application of the robots in industry and other fields depends on efficiency, reliability and the capabilities of the control system which has to ensure successful application of robots in various tasks.

This chapter is devoted to microcomputer systems suitable for controllers of industrial manipulators. As mentioned, a robotic controller represents a single or multi-processor system aimed at driving a robot arm to move in accordance with a user-written program. Robotic controllers are much more complex in their hardware and software structure than most industrial regulators and programmable automata for numerically controlled (NC) machines. The industrial regulators commonly represent PID single-input single-output regulators designed through the use of digital or analog integrated circuits or microcomputers. Some advanced industrial controllers represent self-tuning regulators [1] and automatically adjust parameters (proportional, differential and integral gains) to the parameters of the controlled process. Such a multichannel PID regulator corresponds to the executive level of a robotic controller (see Chap. 4). However, the executive level of an advanced robotic controller can be much more complex than a set of PID regulators when designed to accomplish trajectory following control (in contrast to point-to-point control). The executive module must compensate for dynamic effects of the mechanical arm. This compensation is usually more complex numerically and imposes the need for fast microprocessors. Robot control systems are usually much more complex than programmable automata, which were used earlier to control simple pick-and-place manipulators.

The key requirement when introducing robots into manufacturing systems is the possibility of teaching them quickly to perform the desired task. Hence one of the main factors influencing the effectiveness of robots is their programmability. For this reason, practically all existing robot systems are equipped with tools that facilitate, more or less efficiently, the programming of some specific sets of robotic tasks.

Robots, as flexible machines capable of performing different tasks, are being used more and more in industry, but for some tasks (assembling mechanical parts, for example), it appears that in order to operate successfully robots need feedback information about the state of environment. The necessity for increasing robot adaptability demands the introduction of sensors’ information in control algorithms together with elements of artificial intelligence to gain a higher degree of independence of the robot. In practice, only positional sensors are used as an obligatory part of a robot, with the purpose of feeding the robot control system with information about the state of the robot itself—internal coordinates and their time derivatives.

A great majority of contemporary industrial robots, i.e. their mechanical part, frequently referred to as the manipulator, are in the form of bigger or smaller articulatory (“anthropomorphic”, “arthropoid”) or portal (“gantry”) hoists. These working machines, mostly used for manipulating workpieces, are frequently known as “manipulation robots”, although this is not applicable in a great number of cases (welding, grinding and drilling with a carried electrical tool, etc.). The normal end or manipulator tip is in the form of a terminal organ for gripping in the form of the so-called gripper which can have a diversified design, which will be discussed below.

In previous chapters various aspects of robotics have been studied in detail. Some problems, specific for the application of robotic systems in complex flexible manufacturing, not only in a stand-alone work cell, are also outlined. Awareness that robot ought to be considered as an element of complex automation has been recognized throughout this book.