Chapter 10 - Mechanical actuator systems

Abstract

This chapter focuses on the mechanical actuator systems that consist of hydraulic and pneumatic systems. Hydraulic and pneumatic systems are similar except that while a hydraulic system uses an incompressible fluid as the working medium, a pneumatic system uses air, which is basically compressible. The advantages of using air as the working medium are that it is readily available and no recycling is necessary. The leakage of air does not create a threat to safety as it is non-flammable. It has negligible change in viscosity, which controls the system's performance. The major components of hydraulic and pneumatic systems are pumps (compressors for pneumatic systems), valves, and receiving units such as motors. Pumps are used to supply the high pressure that the mechatronic system requires. The three types of pumps that are most commonly used are the gear pump; the vane pump; and the piston pump. For a clockwise rotation of the gear in gear pumps, fluid is carried between the gear teeth in the same direction from the inlet to the high-pressure discharge side of the pump. The meshing teeth seal the fluid and prevent it from returning to the low-pressure side. In vane pumps, the rotor rotates in a counterclockwise direction, and a large amount of fluid is carried from the inlet to the outlet. This results from the eccentricity of the center of the rotor with respect to that of the housing. The net flow of fluid is a function of the eccentricity, and when it is varied, the vane pump can then be used as a variable-delivery pump. In axial piston pump, the pistons are parallel to and located in the rotor, which is axially driven by the shaft.