53512.3ActuatorsFigure 12.32 Precision translationtable. (UniSlidefrom Velmex,Inc).Common applications that employalead screw includetheworktableforamill,anda varietyofother precision positioning translation tables, such as the one shown in Figure 12.32.PneumaticandHydraulicActuatorsThe term“pneumatic"implies a component or system that uses compressed air as the energysource. On the other hand, a hydraulic system or component uses incompressible oil as the workingfluid. An example of a hydraulic system is the power steering on an automobile; such a system isillustrated in Figure 12.33. Hydraulic fluid is supplied at an elevated pressure from the powersteering pump.When a steering input is made from the driver, the rotaryvalve allows high-pressurefluid to enter the appropriate side of the piston, and aidin turning the wheels.By maintaining a directconnection between the steering column and the rack and pinion, the car can be steered even if thehydraulic system fails.SteeringcolumnRotaryvalveToFluid linesreservoir-FrompumpWFigure12.33SchematicdiagramofapowerRackPistonPinionsteering system
E1C12 09/14/2010 13:54:12 Page 535 Common applications that employ a lead screw include the worktable for a mill, and a variety of other precision positioning translation tables, such as the one shown in Figure 12.32. Pneumatic and Hydraulic Actuators The term ‘‘pneumatic’’ implies a component or system that uses compressed air as the energy source. On the other hand, a hydraulic system or component uses incompressible oil as the working fluid. An example of a hydraulic system is the power steering on an automobile; such a system is illustrated in Figure 12.33. Hydraulic fluid is supplied at an elevated pressure from the power steering pump. When a steering input is made from the driver, the rotary valve allows high-pressure fluid to enter the appropriate side of the piston, and aid in turning the wheels. By maintaining a direct connection between the steering column and the rack and pinion, the car can be steered even if the hydraulic system fails. Figure 12.32 Precision translation table. (UniSlide1 from Velmex, Inc). Pinion Steering column To reservoir From pump Rotary valve Fluid lines Rack Piston Figure 12.33 Schematic diagram of a power steering system. 12.3 Actuators 535
536Chapter12Mechatronics:Sensors,Actuators,andControlsCompressedairinletsPistonsealsPiston rodRodseals andbearingFigure12.34 Construction of a pneumatic cylinder.(Courtesy of ParkerHannifin,Inc.PneumaticActuatorsWhen compressed air is the energy source of choice, a pneumatic cylinder can create linear motion.Ingeneral, the purpose of a pneumaticcylinder is to provide linear motion between two fixedlocations.Figure12.34shows a pneumatic cylinder and acutawayof sucha cylinder.Byapplyinghigh-pressure compressed air to either side of the piston, linear actuation between two definedpositions can easilybeaccomplished.Soleniods"Solenoid"is a term used to describe an electromagnetic device that is employed to create linearmotion of a plunger,as shown inFigure 12.35.The initial force availablefrom a solenoid can bedeterminedfromSNIA(12.21)F82
E1C12 09/14/2010 13:54:12 Page 536 Pneumatic Actuators When compressed air is the energy source of choice, a pneumatic cylinder can create linear motion. In general, the purpose of a pneumatic cylinder is to provide linear motion between two fixed locations. Figure 12.34 shows a pneumatic cylinder and a cutaway of such a cylinder. By applying high-pressure compressed air to either side of the piston, linear actuation between two defined positions can easily be accomplished. Soleniods ‘‘Solenoid’’ is a term used to describe an electromagnetic device that is employed to create linear motion of a plunger, as shown in Figure 12.35. The initial force available from a solenoid can be determined from F ¼ 1 2 ð Þ NI 2 mA d2 ð12:21Þ Figure 12.34 Construction of a pneumatic cylinder. (Courtesy of Parker Hannifin, Inc.) 536 Chapter 12 Mechatronics: Sensors, Actuators, and Controls