Logic Controls in Fluid Power Systems

Chapter: 15

Logic Controls in Fluid Power Systems

"In contrast with the scientist, whose main interest is in discovering new knowledge, the engineer's greatest enjoy- ment derives from creatively solving practi- cal problems."

- Ibid

"The turning point in the process of growing up is when you discover the core of strength within you that survives all hurt."

- A.P.J. Abdul Kalam

"One who fears failure limits his activities. Failure is the only oppor- tunity to more intelligently begin again.' 

- Henry Ford

Learning Objectives

While reading and after studying this chapter, you will be able to:

• Understand the technology of fluidics and how fluidics is used to control fluid power systems. 

• Discuss the construction, operation and purpose of the various fluidic devices.

• Explain the construction, operation and features of the various types of fluid sensors.

• Apply and design fluidic logic circuits for various fluid power systems.

• Understand the distinct features of moving-part logic (MPL) devices.

• Appreciate the role of PLCs in fluid power control systems.

• Apply ladder logic diagrams and Boolean algebra to programmable logic control of fluid power systems.

INTRODUCTION

Whenever some industrial processes or a machine is to be automatically controlled, then a suitable control system is to be employed. The various control methods employed are mechanical control systems, electro-mechanical control systems, electro-hydraulic control systems, electro-pneumatic control systems, hydropneumatic or pneumohydraulic control systems, and electronic control systems.

Nowadays, fluid power industries demand higher machine reliability and the elimination of down time due to component part failure wherever possible. Also, industries demand multifunctional equipment that offers flexibility in control circuits and provision for rapid change-over due to constantly changing manufacturing methods. The conventional types control systems mentioned above prove to be totally inadequate to meet these requirements of industries.

The technology of fluidics (i.e., fluid-logic control system) promises to fulfill most of these requirements. Fluidics is the technology that utilises fluid flow phenomena in components and circuits to perform a wide variety of control functions. These fluid-logic control system is becoming increasingly more popular because it offers some outstanding advantages (such as exceptional thermal and physical stability and ruggedness, insensitiveness to radiation, very minimal vibration and shock, etc.) over the conventional alternate control system methods.

In this chapter, we shall understand the technology of fluidics and how fluidics is used to control fluid power systems. At the end of the chapter, the brief note on moving-part logic (MPL) control systems and programmable logic controllers (PLCs) will also be presented.