Chapter 1. Introduction to Control System The best and most beautiful things in the world cannot be seen or even touched - they must be felt with the heart. Pusan National University Intelligent Robot Laboratory

Table of Contents Introduction System Configurations Analysis and Design Objectives Design Process Computer-aided Design

Introduction Control System definition A control system consists of subsystems and processes assembled for the purpose of obtaining a desired output with a desired performance. A control system produces the output for a given input or response to stimulation. Figure 1.1 Simplified description of a control system

Introduction Two major measures of performance Transient response Steady – state error Figure 1.2 Elevator response

Introduction Advantages of control system Power amplification Remote control Convenience of input form Compensation for disturbances

System Configuration Open – loop system Open-loop system cannot compensate for any disturbances that add to the controller’s driving signal. Mechanical systems are consisting of a mass, spring, and damper. Figure 1.6 Block diagrams of control systems : a. open loop system

System Configuration Closed-loop System Closed-loop systems have the obvious advantages of greater accuracy than open-loop systems. The systems are less sensitive to noise and disturbances. Transient response and steady state error can be controlled more conveniently. Complex and expensive Figure 1.6 Block diagrams of control systems :b. closed loop system

System Configuration Computer – controlled systems In many modern system, the controller is a digital computer. Many loops can be controlled or compensated by the same computer through time sharing. Any adjustments of the compensator parameters required to yield desired response can be made by changes in software.

Analysis and Design Objectives Analysis is the process by which a system’s performance is determined. Design is the process by which a system’s performance is created and changed. Three major objectives of systems analysis and design Producing the desired transient response Reducing steady-state error Achieving stability

Analysis and Design Objectives Transient response Affects the speed of the entire system Too fast a transient response could cause permanent physical damage Steady – state response Resembles the input Accuracy is very important

Analysis and Design Objectives Stability Total response = Natural response + Forced response Natural response describes the way the system dissipates or acquires energy. It is dependent only on the system. Forced response is dependent on the inputs. For a control system to be useful Natural response must eventually approach zero, thus leaving only the forced response. Other Considerations Factors affecting hardware selection Finances Robust design

The Design Process Control system design process Step 1 Step2 Step3 Determine a physical system and specifications from the requirements. Step 1 Draw a functional block diagram. Step2 Transform the physical system into a schematic diagram. Step3 Use the schematic diagram to obtain a block diagram, signal-flow diagram, or state-space representation. Step4 If multiple blocks, reduce the block diagram to a single block or closed-loop system. Step5 Analyze, design, and test to see that requirements and specifications are met. Step6

The Design Process Step 1: Transform requirements into a physical System Transforming the requirements into a physical system Step 2: Draw a functional block diagram The designer now translates a qualitative description of the system into a functional block diagram that describes the component parts of the system. (a) (b) Figure 1.9 Antenna azimuth position control systems : a. system concept; b. detailed layout

The Design Process Step 3: Create a schematic Transforms the physical system into a schematic diagram. Checks the assumptions made about the physical system through analysis and computer simulations. (c) Figure 1.9 Antenna azimuth position control systems : c. schematic

The Design Process Step 4: Develop a mathematical model (Block diagram) Uses physical laws and Newton’s law, along with simplifying assumption, to model the system mathematically. (d) Figure 1.9 Antenna azimuth position control systems : d. functional block diagram

The Design Process Step 5: Reduce the block diagram Reduce this large system’s block diagram to a single block (c) Figure 1.12 Equivalent block diagram for the antenna azimuth position control system

The Design Process Step 6: Analyze and Design Analyzes the system to see if the response specifications and performance requirements can be met by simple adjustments of system parameters. Test input signals are used, both analytically and during testing, to verify the design. TABLE 1.1 Test waveforms used in control systems

Computer – aided Design The use of computers as a computational tool At desktop computers, perform analysis, design, and simulation with one program. Simulate a design rapidly, easily make changes and immediately test a new design. MATLAB

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