Control engineering for mechanical engineers_lec1.pptx

Slide on control

1. Introduction to Hydraulics & Pneumatics Dr. Biplov Kumar Roy Assistant Professor (Mechanical Engineering) Dhaka University of Engineering & Technology DEGREE PROGRAM: B.Sc. in Mechanical Engineering COURSE CODE: ME 4401 COURSE TITLE: Control Engineering

2. INTRODUCTION In the industry we use three methods for transmitting power from one point to another. Mechanical transmission is through shafts, gears, chains, belts, etc. Electrical transmission is through wires, transformers, etc. Fluid power is through liquids or gas in a confined space. In this course, we shall discuss the structure of hydraulic systems and pneumatic systems. Fluid power is the technology that deals with the generation, control, and transmission of forces and movement of mechanical elements or systems with the use of pressurized fluids in a confined system .

3. Hydraulic and Pneumatic Pneumatic Power - Air-powered cylinders Compressed air Either stored on board or injected by a pump Produces linear motion through activation of cylinders Hydraulic Power - Fluid (non-air)-powered cylinders Uncompressible fluid, most often oil . Requires a pump to generate the pressure and flow rate needed. Complex and difficult to build effectively, and costly.

4. Basic Laws Governing To hydraulics & Pneumatics 1. Pascals Law 2.Bernoullies Theorem 3. Continuity Equation 4. Law of Conservation of Energy

5. Pascal's law Pascal’s law states that the pressure exerted on a confined fluid is transmitted undiminished in all directions and acts with equal force on equal areas and at right angles to the containing surfaces. In Fig. 1.1, a force is being applied to a piston, which in turn exerts pressure on the confined fluid. The pressure is equal everywhere and acts at right angles to the containing surfaces. Pressure is defined as the force acting per unit area and is expressed as Pressure p = F/A where F is the force acting on the piston, A is the area of the piston, and p is the pressure on the fluid.

6. Multiplication Of Forces By Pascal's Law The most useful feature of fluid power is the ease with which it is able to multiply force. This is accomplished by using an output piston that is larger than the input piston. Such a system is shown in Fig. 1.2. This system consists of an input cylinder on the left and an output cylinder on the right that is filled with oil. When the input force is Fin on the input piston, the pressure in the system is given by

7. Application of Pascal's law

8. Numerical on Pascal's law Ans : F out = 7111.1 N S in = 14.4mm

9. Ans a,b,c =1.132MPa Ans d Force in cylinder B=8888N

10. Components of Hydraulic System Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a fluid for transmitting energy from an energy-generating source to an energy-using point to accomplish useful work. Figure shows a simple circuit of a hydraulic system with basic components .

11. Hydraulic System Block Diagram of Hydraulic System

12. Components of Hydraulic System

13. Components of Pneumatic System A pneumatic system carries power by employing compressed gas, generally air, as a fluid for transmitting energy from an energy-generating source to an energy-using point to accomplish useful work. Figure shows a simple circuit of a pneumatic system with basic components.

14. Hydraulic System Block Diagram of Pneumatic System

15. Comparison of Hydraulic & Pneumatic System

16. Comparison of H&P system with conventional Transmission system

17. Hydraulic System Advantages The hydraulic system uses incompressible fluid which results in higher efficiency. It delivers consistent power output which is difficult in pneumatic or mechanical drive systems. Hydraulic systems employ high-density incompressible fluid. The possibility of leakage is less in the hydraulic system as compared to that in the pneumatic system. The maintenance cost is less. These systems perform well in hot environmental conditions. Disadvantages The material of the storage tank, piping, cylinder, and piston can be corroded with the hydraulic fluid. Therefore one must be careful while selecting materials and hydraulic fluid. The structural weight and size of the system is more which makes it unsuitable for smaller instruments. The small impurities in the hydraulic fluid can permanently damage the complete system, therefore one should be careful and a suitable filter must be installed. The leakage of hydraulic fluid is also a critical issue and suitable prevention methods and seals must be adopted. The hydraulic fluids, if not disposed of properly, can be harmful to the environment.

18. Applications of hydraulic systems Applications of hydraulic systems Hydraulic systems are mainly used for precise control of larger forces. The main applications of hydraulic systems can be classified into five categories: Industrial: Plastic processing machinery, steel making, primary metal extraction applications, automated production lines, machine tool industries, paper industries, loaders, crushes, textile machinery, R & D equipment, and robotic systems, etc. Mobile hydraulics: Tractors, irrigation systems, earthmoving equipment, material handling equipment, commercial vehicles, tunnel boring equipment, rail equipment, building, and construction machinery and drilling rigs, etc. Automobiles: It is used in the systems like breaks, shock absorbers, steering systems , windshields, lifts, and cleaning, etc. Marine applications: It mostly covers ocean-going vessels, fishing boats, and naval equipment. Aerospace equipment: There are equipment and systems used for rudder control, landing gear, breaks, flight control, transmission, etc. which are used in airplanes, rockets and spaceships.

19. Hydraulic Fluids A hydraulic fluid is the transmitting medium of a hydraulic system. In fluid power systems, a hydraulic fluid has to perform various functions such as the following: 1. Power transmission : To transmit power, which is the primary function. 2. Lubrication : To lubricate various parts, so as to avoid metal-to-metal contact and reduce friction, wear and heat generation. 3. Sealing : To seal the moving elements to avoid leakage. 4. Cooling : To carry away the heat generated in the system and to dissipate the heat through a reservoir or a heat exchanger. 5. Contaminant removal : To carry along the contaminations to the tank, where they can be removed through filters.