Bishop, Robert H. - The Mechatronics Handbook [CRC Press 2002] Part 16 ppt

relatively inexpensive because, for multiple signal lines, only one common line is required; however, this type of interface is susceptible to induced and ground noise and is not suitable for high-speed communi- cation over long distances. The ground noise is associated with voltage drop in a common return line, while the induced noise comes from interfering electromagnetic fields. Both types of noise can come from external sources or from neighboring transmission circuits. A remedy can be the use of coaxial cable, shielded cable, and/or the use of separate return lines for individual signals. These additional measures tend to increase the cost of the interface. The balanced (differential) transmission mode has much better noise immunity than the unbalanced mode. Two complementary signal lines carry the data signal. The implementation often involves two single- ended drivers driving a twisted-pair transmission line. Figure 37.3 shows an example of balanced data transmission with two channels and five wires. As in Fig. 37.2, symbol D represents driver and symbol R receiver. Symbol T represents termination resistor. Use of a termination resistor at the receiver end of the transmission line is critical for high-speed communications over long distances as unterminated transmis- sion lines can cause severe distortion of signals. Both induced and ground noises appear on both conductors as common-mode signals that are rejected by the differential receiver. The differential signals carrying data are amplified while the common-mode noise signals are suppressed. As a result, the balanced data trans- mission lines can be used for longer distances with higher transmission rates. Both unbalanced and balanced interfaces shown in Figs. 37.2 and 37.3 represent two simplex interfaces, which can form one full-duplex point-to-point (see below) communication channel. A good source of information on individual drivers and receivers is provided in the data sheets and application notes of semiconductor manufacturers [1,2]. Point-to-Point vs. Multi-Point If communication takes place between two devices, we call such a communication link a point-to-point link. In mechatronic systems, it is often required for the master system to communicate with a number of subsystems. Cost permitting, a number of point-to-point data transmission lines can be implemented. In a point-to-point arrangement, the master system has a point-to-point connection to each individual subsystem, i.e., there is a separate port and communication line for each subsystem. This type of arrange- ment is shown in Fig. 37.4. The connection can also be arranged as a multi-point connection in which FIGURE 37.2 Example of an unbalanced data transmission. FIGURE 37.3 Example of a balanced data transmission. D D R R D D R R T T ©2002 CRC Press LLC 38 Communications and Computer Networks 38.1 A Brief History 38.2 Introduction 38.3 Computer Networks Wide Area Computer Networks • Local and Metropolitan Area Networks • Wireless and Mobile Communication Networks 38.4 Resource Allocation Techniques 38.5 Challenges and Issues 38.6 Summary and Conclusions The field of communications and computer networks deals with efficient and reliable transfer of infor- mation from one point to another. The need to exchange information is not new but the techniques employed to achieve information exchange have been steadily improving. During the past few decades, these techniques have experienced an unprecedented and innovative growth. Several factors have been and continue to be responsible for this growth. The Internet is the most visible product of this growth and it has impacted the life of each and every one of us. This chapter describes salient features and operational details of communications and computer networks. The contents of this chapter are organized in several sections. Section 38.1 describes a brief history of the field of communications. Section 38.2 deals with the introduction of communication and computer networks. Section 38.3 describes operational details of computer networks. Section 38.4 discusses resource allocation mechanisms. Section 38.5 briefly describes the challenges and issues in communication and computer networks that are still to be overcome. Finally, Section 38.6 summarizes the article. 38.1 A Brief History Exchange of information (communications) between two or more entities has been a necessity since the existence of human life. It started with some form and shape of human voice that one entity can create and other(s) can listen to and interpret. Over a period of several centuries, these voices evolved into languages. As the population of the world grew, more and more languages were born. For a long time, languages were used for face-to-face communications. If there were ever a need to convey some information (a message) over a distance, someone would be briefed and sent to deliver the message to a distant site. Gradually, additional methods were developed to represent and exchange the information. These methods included symbols, shapes, and eventually alphabets. This development facilitated information recording and use of nonvocal means for exchanging information. Hence, preservation, dissemination, sharing, and com- munication of knowledge became easier. Until about 150 years ago, all communication was via wireless means and included smoke signals, beating of drums, and use of reflective surfaces for reflecting light signals (optical wireless). Efficiency of Mohammad Ilyas Florida Atlantic University ©2002 CRC Press LLC 39 Fault Analysis in Mechatronic Systems 39.1 Introduction 39.2 Tools Used for Failure/Reliability Analysis 39.3 Failure Analysis of Mechatronic Systems 39.4 Intelligent Fault Detection Techniques 39.5 Problems in Intelligent Fault Detection 39.6 Example Mechatronic System: Parallel Manipulators/Machine Tools Parallel Architecture Manipulators (Based on a Paper by Huang and Notash 1999) • Tool Condition Monitoring 39.7 Concluding Remarks 39.1 Introduction As the degree of automation increases, particularly intelligent automation, high reliability, fail-safe and fault tolerance become an essential part of the mechatronic system design. A mechatronic system is reliable if no failure and malfunction could result in an unsafe system; is safe if it causes no injury or damage to the operator, environment and system itself; is fail-safe if the system could be stopped safely after the failure; and is fault tolerant if the system could complete its task safely after any failure. Fault/failure corresponds to any condition or component/subsystem degradation (sharp or graceful degradation) that affects the performance of a system such that the system cannot function as it is required. As the application of the mechatronic systems expands to areas such as highly dynamic/unstructured or space/remote environments, medical and high-speed applications, the necessity for the system to be fail- safe (could stop with no harm to the environment, operator, and itself) and fault tolerant (tolerate the failure and complete the assigned task) increases. A mechatronic system is called fault tolerant if after any failures there will be no interruption in the task/operation of the system. Fault tolerance and high reliability could be achieved by using high quality components, through design and robust control, and by incorporating redundancy in the design of mechatronic systems. A mechatronic system consists of mechanical, electrical, computer, and control (hardware and software) subsystems. Therefore, their redundancy could be in the form of hardware redundancy (redundancy in sensing, actuation, transmission, communication, and computing), software redundancy, analytical redundancy, information redundancy, and time redundancy. 39.2 Tools Used for Failure/Reliability Analysis The failure analysis techniques could be classified as inductive techniques and deductive techniques (Wolfe, 1978). Inductive techniques, such as decision or event trees and failure modes and effects analysis (FMEA), consider the possible states of components/subsystems and determine their effects on the system, i.e., Leila Notash Queen’s University Thomas N. Moore Queen’s University ©2002 CRC Press LLC 40 Logic System Design 40.1 Introduction to Digital Logic Logic Switching Levels • Logic Gate Application 40.2 Semiconductor Devices Diode • Bipolar Transistor • Field Effect Transistor (FET) 40.3 Logic Gates 40.4 Logic Design Minimization • Dynamic Characteristics • Other Design Considerations 40.5 Logic Gate Technologies Resistor–Transistor Logic (RTL) • Diode–Transistor Logic (DTL) • Transistor–Transistor Logic (TTL) • Emitter-Coupled Logic (ECL) • CMOS Logic 40.6 Logic Gate Integrated Circuits 40.7 Programmable Logic Devices (PLD) 40.8 Mechatronics Application Example 40.1 Introduction to Digital Logic In analog electronics, voltages and current represent variables that vary continuously from the allowable minimum to the maximum. These variables are measured, amplified, added, and subtracted through analog circuits to achieve the desired results. For instance, measurement of temperature using thermo- couples requires the amplification of voltages generated to a suitable range, calibration of the voltage with measured temperatures, and outputting the results on a voltmeter to indicate temperature. In this design, it may be necessary to subtract an offset voltage, multiply with a gain factor depending on the temperature range. The amplification of voltages and current are accomplished easily with operational amplifiers and transistors, respectively. The measured temperature can be used as the feedback signal in a control loop for a mechatronic temperature control system. In digital electronics, the variables assume a binary state, assuming a value of 0 or 1. In the above example, we might want to shut the solenoid valve down if the temperature was below desired value and open the valve if the temperature was above that value. In this case, we simply require a TRUE or FALSE input to the question “Is the temperature above or below the threshold?” The representation of these types of variables in circuits, which assume binary values, and their manipulation to achieve desired results is the topic of discussion in this chapter. Logic Switching Levels In digital circuits, voltage levels indicate binary states where the HIGH or TRUE state is represented by the maximum voltage value, typically 5 V, and the LOW or FALSE state is represented by the minimum voltage value, typically 0 V. In Boolean logic,“1” represents TRUE and “0” represents FALSE. In practice, any voltage above a minimum input threshold, V IH , is interpreted as logic HIGH and any voltage below M. K. Ramasubramanian North Carolina State University ©2002 CRC Press LLC 41 Synchronous and Asynchronous Sequential Systems 41.1 Overview and Definitions Synchronous Sequential Systems • Flip-Flops and Latches • Mealy and Moore Models • Pulsed and Level Type Inputs • State Diagrams 41.2 Synchronous Sequential System Synthesis Design Steps 41.3 Asynchronous Sequential System Synthesis Design Steps 41.4 Design of Controllers’ Circuits and Datapaths 41.5 Concluding Remarks 41.1 Overview and Definitions Traditionally, digital systems have been classified into two general classes of circuits: combinational and sequential systems. Combinational systems are logic circuits in which outputs are determined by the present values of inputs. On the other hand, sequential systems represent the class of circuits in which the outputs depend not only on the present value of the inputs, but also on the past behavior of the circuit. In most systems a clock signal is used to control the operation of a sequential logic. Such a system is called a synchronous sequential circuit. When no clock signal is used, the system is referred to as asynchronous . Synchronous Sequential Systems Figure 41.1 shows the general structure of a synchronous sequential system. The circuit has a set of primary inputs and produces a set of primary outputs . In addition, it has sets of secondary inputs and outputs, and , respectively. These sets of signals are inputs and outputs to state (or memory) elements or devices called flip-flops (FFs) or latches . The outputs of these devices constitute the present states , while the inputs constitute the next states or . There are several types of such devices, as well as many variations of these types, namely, set-reset (SR), delay (D), trigger (T), and JK (a combination of SR and T) FFs and latches. Table 41.1 shows the behavior of each of these types. Flip-Flops and Latches The outputs of the FFs or latches, which are sequential devices, are determined by the present values of their inputs as well as the values of their present states. However, FFs are edge-triggered devices, meaning that state transitions might take place only during one clock cycle. This clock transition is either positive edge X Z Q + Q Q Q + Sami A. Al-Arian University of South Florida ©2002 CRC Press LLC 42 Architecture 42.1 Introduction 42.2 Types of Microprocessors 42.3 Major Components of a Microprocessor Central Processor • Input/Output Subsystem • System Interconnection 42.4 Instruction Set Architecture 42.5 Instruction Level Parallelism Dynamic Instruction Execution • Predicated Execution • Speculative Execution 42.6 Industry Trends Computer Microprocessor Trends • Embedded Microprocessor Trends • Microprocessor Market Trends 42.1 Introduction The microprocessor industry is divided into the computer and embedded sectors. Both computer and embedded microprocessors share aspects of computer design, instruction set architecture, organization, and hardware. The term “computer architecture” is used to describe these fundamental aspects and, more directly, refers to the hardware components in a computer system and the flow of data and control information among them. In this chapter, various types of microprocessors will be described, fundamen- tal architecture mechanisms relevant in the operation of all microprocessors will be presented, and microprocessor industry trends discussed. 42.2 Types of Microprocessors Computer microprocessors are designed for use as the central processing units (CPU) of computer systems such as personal computers, workstations, servers, and supercomputers. Although microproces- sors started as humble programmable controllers in the early 1970s, virtually all computer systems built in the 1990s use microprocessors as their central processing units. The dominating architecture in the computer microprocessor domain today is the Intel 32-bit architecture, also known as IA-32 or X86. Other high-profile architectures in the computer microprocessor domain include Compaq-Digital Alpha, HP PA-RISC, Sun Microsystems SPARC, IBM/Motorola PowerPC, and MIPS. Embedded microprocessors are increasingly used in consumer and telecommunications products to satisfy the demands for quality and functionality. Major product areas that require embedded micropro- cessors include digital TV, digital cameras, network switches, high-speed modems, digital cellular phones, video games, laser printers, and automobiles. Future improvements in energy consumption, fabrication cost, and performance will further enable new applications such as the hearing aid. Many experts expect that embedded microprocessors will form the fastest growing sector of the semiconductor business in the next decade. 1 Daniel A. Connors University of Colorado at Boulder Wen-mei W. Hwu University of Illinois at Urbana-Champaign ©2002 CRC Press LLC . inputs. On the other hand, sequential systems represent the class of circuits in which the outputs depend not only on the present value of the inputs, but also on the past behavior of the circuit FFs and latches. Table 41.1 shows the behavior of each of these types. Flip-Flops and Latches The outputs of the FFs or latches, which are sequential devices, are determined by the present. another. The need to exchange information is not new but the techniques employed to achieve information exchange have been steadily improving. During the past few decades, these techniques have