UNIT-6Basic Mechanical Engineeringf.pptx

Basic Mechanical Engineering

1. UNIT-6 Control systems

2. System: A Number of elements or Components Connected in a sequence to perform a specific function the group thus formed is called a system.

3. Control system:   Control system is a device or set of devices , that manages, commands, directs or regulates the behavior of other devices or systems .

4. Input: The Excitation or command signal applied to a control system from an external energy source to produce a specified response from the system. Out put: The Actual response obtained from a control system is called output.

5. Importance of control system: Control theory has played vital role in the Advance of science and technology. Industrial progress through Automation is achieved by Automatic process control system. Automatic control has become an integral part of modern manufacturing , industrial processes and human life. Successful operation of space vehicles will depend on proper functioning of large number of control systems. Industrial control systems are used in industrial production for controlling equipment's or machines.

6. Control System Terminology Disturbance Manipulated variable

7. Process, Plant or Controlled : A Body, Process or Machine of which particular quantity or condition to be controlled. Ex: Furnace, Reactor or Space craft Error or Actuating signal: An Algebraic sum of the Reference input and primary feed back. Manipulated variable: The quality or condition that is varied as a function of the actuating signal so as to change the plant by the control element.

8. Primary Feedback Signal: A function of the controlled output which is compared with the reference input to obtain the actuating signal. Error-Detector: An element that detects the feed back, It is a summing point which gives a algebraic summation of two or more signals. Disturbance: An undesired variable applied to the system which tends to affect adversely the value of the variable being controlled.

9. Feed back element: An element of the feed back control system that establishes a functional relationship between the controlled variable and the feed back signal. Control element: An element that is required to generate the appropriate control signal (Manipulated variable) applied to the plant. Forward and Backward Paths: The Transmission path from the actuating signal to the controlled output constitutes the Forward path.

10. Manual Control System Input signal Rate of flow Out put (Controlled) Force (Command) Speed Accelerator Pedal, Linkages and Carburetor Engine vehicle

11. Electrical switch on off system Thermal system(manual feed back system) Examples of control system

12. Driving System of an Automobile Input(Command) out put(controlled) Signal force variable speed Accelerator Pedal, Linkages and Carburetor Engine Vehicle

13. Automobile Steering System Direction of car Position of automobile Brain Hands Steering Wheel Eye Error

14. Biological Control System

15. Automatic control system Automatic control is the maintenance of a desired value of quantity or condition by measuring the existing value, comparing it to the desired value and employing the difference to intimate action for reducing this difference.

16. Automatic Tank level control System

17. Advantages of Automatic control systems: Increase in quantity of Product. Increase in Quality of Product. Elimination of Human Error. Improvement of Human Product. Savings in Energy Requirements. Increase in efficiency of a plant.

18. Applications of Automatic control systems used in Industries: Processing industries: such as Petroleum, Chemical, Steel, Power and Food for the Control of Temperature and Pressure and Flow. Transportation systems: such as Railways, Aero planes, Free Missiles and Ships. Good Manufacture: such as Automobile parts, Refrigerators, and Radio for the control of assembly operations, Work flow, Heat treating etc. Power machines: such as Machine tools, Compressors and Pumps, Prime movers and electric power supply units for the control of Position, Speed and Power.

19. Examples of Automatic Control System Thermal system Water level control system

20. Classification or Types of control systems There are two types of Control systems 1. Open Loop Control Systems 2. Closed Loop Control Systems

21. 1. Open Loop Control Systems

22. Advantages: 1. Moderate accuracy 2. simple and economical. 3. Easier to construct. 4. Stable System. Disadvantages: 1. Sensitive to surrounding condition like vibrations, voltage, etc. 2. In accurate and unreliable. 3. The changes in the output due to external disturbances are not corrected automatically. 4. Slow response to input command changes thereby making system slow and sluggish.

23. Examples: Automatic toaster system. Traffic signaling system. Home heater where there is no provision for sensing, feedback and control.

24. 2. Closed Loop Control Systems

25. Advantages: 1. High accuracy 2. Fast response to input signals. 3. Independence to operating conditions. 4. Sensitivity of the systems may be made small to make the system more stable. Dis Advantages: 1. Complex and costlier. 2. Feedback element reduces the over all gain of the system. 3. Feedback element may lead to oscillatory response(Hunting). 4. Steady state error due to friction, inertia, backlash etc.

26. Examples: Home heating system. Human System. Traffic flow control system. Speed Control system.

27. Differences between open loop and closed loop control system Open loop control system No Feed back element. Moderate Accuracy. Simple and Economic. Slow Response to input command signal. Does not Automatically rectify the variations in its out put. Closed loop control system Feed back element is provided. High Accuracy. Complex and Costlier. Fast Response to input signal. Automatically rectifies the variations in its out put.

28. 6. Control adjustment depends on human judgement and estimate. 7. Always stable. 8. Examples: Automatic toaster system, Traffic signaling system. Home heater where there is no provision for sensing, feedback and control. 6. Control adjustment is done Automatically by feed back element. 7. Tendency to oscillate. 8. Examples: Home heating system. Human System. Traffic flow control system. Speed Control system.

29. SERVO MECHANISMS Servo mechanisms or servo is restricted to feed back control system in which the controlled variable is a mechanical position or time derivatives of position. Position control systems used in servo mechanisms. Automatic device that uses error-sensing to correct the performance of a mechanism and is defined by its function.

30. 1.Open loop position control system(Servo mechanism)

31. Amplifier Dc Shunt motor Load Block Diagram

32. 1.Closed loop position control system(Servo mechanism)

33. Block diagram of closed loop position control system

34. Applications: Machine tool position control Constant tension control of sheet rolls in paper mills Control of sheet metal thickness in hot rolling mills Radar tracking systems Missile guidance systems Inertial guidance, roll stabilization of ships.

35. Open loop temperature control system Digital Display Relay control circuit Ac Supply

36. Closed loop temperature control system

37. Open loop speed control system

38. Closed loop speed control system

39. High gain amplifier Dc Servomotor L O a d Speed Tachometer