Chapter 9 Actuators

Chapter 9

Actuators

Workhorses offy the System

1 Objectives

. Describe the construction and operation of basic hydraulic cylinders, limited-rotation actuators, and motors. . Compare the design and operation of various types of hydraulic cylinders. . Select appropriate cylinder design options available for mounting hydraulic cylinders and reducing hydraulic shock. . Compare the design and operation of various types of hydraulic motors.

Objectives

. Contrast the operation of fixed- and variable- speed hydraulic motors. . Describe the construction and operation of a basic hydrostatic transmission. . Size hydraulic cylinders and motors to correctly meet system force and speed requirements. . Interpret manufacturer specifications for hydraulic cylinders.

2 Hydraulic Cylinders

. Actuators are the components used in a hy drau lic syst em t o provid e power t o a requi red work location . Cylinders are the hydraulic system components that convert fluid pressure and flow into linear mechanical force and movement

Hydraulic Cylinders

. A basic cylinder consists of: – Piston – Piston rod – Barrel

3 Hydraulic Cylinders

. Parts of a typical cylinder

Hydraulic Cylinders

. The piston forms sealed, variable-volume chbhambers i ithlidn the cylinder . System fluid forced into the chambers drives the piston and rod assembly . Linear movement is produced

4 Hydraulic Cylinders

. Seals prevent leakage between: – Piston and cylinder barrel – Piston rod and head – Barrel and its endpieces . Wiper seal, or scraper, prevents dirt and water from entering the cylinder during rod retraction

Hydraulic Cylinders

. Various seals are used in a cylinder

5 Hydraulic Cylinders

. Rod wipers prevent contitiftamination from entering on rod retraction

IMI Norgren, Inc. © Goodheart-Willcox Co., Inc. 11 Permission granted to reproduce for educational use only.

Hydraulic Cylinders

. Cylinders are typically classified by operating priilinciple or b y const ructi titon type – Single-acting or double-acting – Tie rod, mill, threaded end, or one piece

6 Hydraulic Cylinders

. Single- and double-acting cylinders

Single-acting Double-acting

Hydraulic Cylinders

. Single-acting cylinders exert force either on extitension or ret ttiraction . They require an outside force to complete the second motion

7 Hydraulic Cylinders

. Double-acting cylinders generate force during bthboth ext ensi on and ret racti on – Directional control valve alternately directs fluid to opposite sides of the piston – Force output varies between extension and retraction

Hydraulic Cylinders

. Effective piston area is reduced on retraction due to the rod cross section

8 Hydraulic Cylinders

. Volume is reduced on retraction

Hydraulic Cylinders

. External tie rod bolts are used to secure the endthds on the tie-rodlidd cylinder didesign – Commonly found on heavy industrial machines – External tie rods increase chance of damage and promote accumulation of dirt

9 Hydraulic Cylinders

. Tie-rod cylinder

Hydraulic Cylinders

. Mill cylinders

Yates Industries, Inc.

10 Hydraulic Cylinders

. Threaded-end cylinder

Bailey International Corporation

Hydraulic Cylinders

. One-piece cylinder has the cylinder barrel welded t o th e end s . Produces a compact actuator – Cost effective to manufacture – Cannot be serviced (throwaway)

11 Hydraulic Cylinders

. Hydraulic ram is commonly used in hand- operatdjted jack s – Rod is basically the same diameter as the inside of the cylinder barrel – Large-diameter rod is more rigid under load, but cylinder can generate force in only one direction

Hydraulic Cylinders

. Typical hand-operated jack

12 Hydraulic Cylinders

. Telescoping cylinders are available for applicati ons requi ri ng l ong ext ensi on di st ances – Rod is made up of several tubes of varying size nested inside of the barrel – Each tube extends, producing a rod longer than the cylinder barrel – Typical example is the actuator that raises the box on a dump truck

Hydraulic Cylinders

. Telescoping cylinders

Star Hydraulics, Inc.

13 Hydraulic Cylinders

. Cylinders often use hydraulic cushions – Provide a controlled approach to the end of the stroke – Reduces the shock of the impact as the piston contacts the cylinder head

Hydraulic Cylinders

. Cylinder cushioning device

14 Hydraulic Cylinders

. A variety of mounting configurations are used to att ach th e cyli nd er b od y and rod end t o machinery – Fixed centerline – Fixed noncenterline – Pivoting centerline – Expected cylinder loading is the major factor in the selection of the mounting style

Hydraulic Cylinders

. Head-end flange mount

15 Hydraulic Cylinders

. Fixed-noncenterline mount

Hydraulic Cylinders

. Pivoting-centerline, clevis mount

16 Hydraulic Cylinders

. Pivoting-centerline, trunnion mount

Hydraulic Cylinders

. The force generated by a cylinder is calculated by mu ltipl yi ng th e eff ecti ve area of th e pi st on by the system pressure

17 Hydraulic Cylinders

. Effective cylinder piston area

Hydraulic Cylinders

. Force generated during the extension of a double-acting cylinder with a single -ended rod is calculated as:

Ef = Sp  Pa where: Ef = extension force Sp = system pressure Pa = piston area

(Calculations require consistent units of measure in these formulas)

18 Hydraulic Cylinders

. Force generated during the retraction of a dbldouble-acting cyli nd er with a si ngl e-enddded rod is calculated as: Rf = Sp  (Pa – Ra) where: Rf = retraction force Sp = system pressure Pa = piston area Ra = rod area

Hydraulic Cylinders

. Speed at which the cylinder extends or retracts idtis determi ned db by: – Physical volume per inch of cylinder piston travel – Amount of fluid entering the cylinder . Effective area of the piston is used to calculate the volume of the cylinder per inch of piston travel

19 Hydraulic Cylinders

. Extension speed of a double-acting cylinder with a si ngl e-enddded ro did is ca lcu ltdlated as: Es = Fr  (Cg  Pa) where: Es = extension speed Fr = flow delivery rate Cg = cubic inches in one gallon Pa = piston area

Hydraulic Cylinders

. Calculate retraction speed of a double-acting cylind er with si ngl e-enddded rod as: Rs = Fr  [Cg  (Pa – Ra)] where: Rs = retraction speed Fr = flow delivery rate Cg = cubic inches in one gallon Pa = piston area Ra = rod area

20 Hydraulic Cylinders

. Flow rate to produce a desired extension or retracti on speed di is cal cul ltdated as: Fr = (Ea  Cs)  Cg where: Fr = system flow rate Ea = effective piston area Cs = cylinder speed Cg = cubic inches in one gallon

Hydraulic Cylinders

. Hydraulic cylinder manufacturers provide det ail ed specifi cati ons concerni ng: – Construction – Physical size – Load capacity

21 Hydraulic Cylinders

. This information includes basic factors such as: – Bore – Stroke – Pressure rating – Other details, such as service rating, rod end configg,urations, and dimensions

Hydraulic Cylinders

. Typical manufacturer’s catalog page

Bailey International Corporation

22 LimitedLimited--RotationRotation Hydraulic Actuators . Limited-rotation devices are actuators with an output sh hftthttaft that typi call y appli es t orque through approximately 360° of rotation . Models are available that are limited to less than one revolution, while others may produce several revolutions

LimitedLimited--RotationRotation Hydraulic Actuators . Most common designs of limited-rotation actttuators are: – Rack-and-pinion –Vane – Helical piston and rod

23 LimitedLimited--RotationRotation Hydraulic Actuators

. Rack-and-pinion limited rotation actuator

IMI Norgren, Inc.

LimitedLimited--RotationRotation Hydraulic Actuators . Vane limited-rotation actuator

24 LimitedLimited--RotationRotation Hydraulic Actuators . Helical piston and rod limited-rotation actuator

LimitedLimited--RotationRotation Hydraulic Actuators . Limited-rotation actuators are used to perform a number of ff functi ons i n a vari itety of fid indust tilrial situations – Indexing devices on machine tools – Clamping of workpieces – Oppgeration of large valves

25 LimitedLimited--RotationRotation Hydraulic Actuators . Limited-rotation actuators are used in this robtibotic arm

IMI Norgren, Inc. © Goodheart-Willcox Co., Inc. 51 Permission granted to reproduce for educational use only.

Hydraulic Motors

. Hydraulic motors are called rotary actuators . They convert fluid pressure and flow into torque and rotational movement

26 Hydraulic Motors

. Typical hydraulic motor application

Hydraulic Motors

. All basic hydraulic motors consist of three component groups: – Housing – Rotating internal parts – Power output shaft

27 Hydraulic Motors

. Parts of a typical hdhydrau lic mot or

Hydraulic Motors

. System fluid enters the housing and applies pressure tthttiitto the rotating internal part s . This, in turn, moves the power output shaft and applies torque to rotate a load

28 Hydraulic Motors

. Primary parts that produce the rotating motion in most h yd rauli c mot ors are eith er: – Gears – Vanes – Pistons

Hydraulic Motors

. Four requirements of a motor

29 Hydraulic Motors

. Displacement of a hydraulic motor indicates the vol ume of fl u id need ed t o t urn th e out put shaft one revolution – Fixed displacement – Variable displacement

Hydraulic Motors

. In a fixed-displacement motor: – Internal geometry cannot be changed – Same volume needed per output shaft revolution

30 Hydraulic Motors

. In a variable-displacement motor: – Internal geometry can be changed – Displacement per shaft revolution can be adjusted – Motor can operate at variable speeds with a constant input flow

Hydraulic Motors

. Hydraulic motors may be classified by the type oflf load appli lidted to th e b eari ngs of fth the out put shaft – Unbalanced indicates the output shaft is loaded from one side, side loading the shaft bearings – Balanced indicates the bearing load is balanced by use of two inlet ports arranged opposite of each other and two outlet ports similarly arranged

31 Hydraulic Motors

. The external gear hydraulic motor is the most common andid simpl est tfthb of the basi c mot or t ypes – Fixed displacement – Unbalanced load on the bearings

Hydraulic Motors

. The most common internal gear motor has a gerotor design

Courtesy of Eaton Fluid Power Training

32 Hydraulic Motors

. The specially shaped gear teeth of the gerotor fiblform variable-volhbthtlllume chambers that allow system fluid flow and pressure to turn the motor output shaft . Gerotor motors are fixed-displacement units operating with an unbalanced bearing load

Hydraulic Motors

. An orbiting gerotor motor is a variation of the bibasic gerot or d diesign – Uses a fixed outer gerotor gear with internal teeth and an inner gear with external teeth – Center point of the inner gear orbits around the center point of the fixed gear with internal teeth – Motor operates at a slower speed, but has a higher torque output

33 Hydraulic Motors

. Orbiting gerotor motor

Courtesy of Eaton Fluid Power Training

Hydraulic Motors

. Basic vane motor has a slotted rotor located off center in a circular chamber and fitted with movable vanes – Space between the vanes creates a number of variable-sized chambers – Forcing fluid into the small-size chambers causes the volume of the chambers to increase, turning the motor shaft – Basic vane motor is fixed displacement with an unbalanced bearing load

34 Hydraulic Motors

. Basic vane motor

Hydraulic Motors

. Balanced vane motors evenly distribute the ldload on th thbie bearings – Achieved by operating the rotor and vanes in a slightly oblong chamber – Allows two inlet ports and two outlets ports to be used in the motor – Placing ports opposite each other balances bearing loading

35 Hydraulic Motors

. A basic, balanced vane motor

Hydraulic Motors

. Vane motors are available as either fixed or varibldiliable displacement . The variable-displacement feature allows an operator to change the speed of a motor without changing the system flow rate

36 Hydraulic Motors

. In variable-displacement designs, the chamber ihihthtin which the rotor and vanes operat tie is contained in a moveable ring – When the center point of the rotor and ring are concentric, the displacement is zero – Moving the ring so the center points are not concentric increases the motor displacement and changes motor speed

Hydraulic Motors

. Piston motors are available having either fixed or varibldiliable displacement s . In variable-displacement designs, the length of the piston stroke is changed to vary the volume of fluid needed to rotate the motor one revolution

37 Hydraulic Motors

. Two basic classifications of piston motors are axilial pi itston and radi dilital piston – An axial piston motor has pistons with centerlines parallel to the axis of the output shaft – A radial piston motor has pistons with centerlines perpendicular to the axis of the output shaft

Hydraulic Motors

. Axial piston motor

The Oilgear Company

38 Hydraulic Motors

. Axial piston motors are available in two configura tions: – Inline – Bent axis

Hydraulic Motors

. In an inline piston motor: – Centerline of the barrel is concentric with the centerline of the power output shaft – A swash plate transmits force from the pistons to the shaft

39 Hydraulic Motors

. Inline piston motor

The Oilgear Company © Goodheart-Willcox Co., Inc. 79 Permission granted to reproduce for educational use only.

Hydraulic Motors

. In a bent-axis piston motor: – Centerline of the barrel is at an angle to the centerline of the output shaft – A universal joint and other fittings are used to transmit force between the barrel and the output shaft

40 Hydraulic Motors

. Bent-axis piston motor

Courtesy of Eaton Fluid Power Training

Hydraulic Motors

. A number of alternate motor designs are used iilidhdlilitiin specialized hydraulic applications – Screw motor designs for quiet, continuous operation – Special piston-motor designs allowing the direct mounting and drive of wheels for off-road, heavy- transport vehicles

41 Hydraulic Motors

. Hydraulic motors may be incorporated into ciitiircuits using seri es or parall lllel connecti ons – Series circuits: total system pressure is determined by adding the loads placed on each unit – Parallel circuits: each motor receives full system pressure; loads must be matched or equal flow supplied to each motor if constant speed is desired from each unit

Hydraulic Motors

. Motors in series

42 Hydraulic Motors

. Motors in parallel

Hydraulic Motors

. Motors in parallel with flow control

43 Hydraulic Motors

. Braking circuits are used to slow hydraulic motttors to a st op – Inertia of a heavy rotating load can continue to turn the motor shaft – Braking occurs when fluid discharged from the motor outlet port is forced to pass through an adjustable pressure control valve before returning to the reservoir

Hydraulic Motors

. Braking circuit

44 Hydraulic Motors

. An open-loop hydraulic motor system uses a lttilfbihdlitlayout typical of a basic hydraulic system – Pump moves fluid from a reservoir, through a directional control valve, to the motor – Fluid is then returned from the motor to the reservoir through the same control valve

Hydraulic Motors

. Closed-loop hydraulic motor systems continuousl y ci rcul at e fl uid b et ween th e pump and the motor without returning it to a system reservoir . These systems use a replenishment circuit to replace fluid lost through leakage

45 Hydraulic Motors

. Replenishment circuit

Hydrostatic Drives

. Hydrostatic drive systems consist of the basic components typically found in other hydraulic motor circuits

46 Hydrostatic Drives

. Hydrostatic drives provide effective tiiftransmission of power and dll allow easy adjustment and control of: – Output shaft speed – Torque – Horsepower – Direction of rotation

Hydrostatic Drives

. When compared to conventional transmissions, hdhydros ttiditatic drives: – Have a high power output–to–size ratio – May be stalled under full load with no internal damage – Accuratelyyp maintain speed under var ygying load conditions – Provide an almost infinite number of input/output speed ratios

47 Hydrostatic Drives

. Hydrostatic drives may be open or closed ciitircuits – Open circuit has the layout of a basic hydraulic motor circuit – Closed circuit has the outlet of the pump directly connected to the inlet of the motor and the outlet of the motor directly connected to the inlet of the pump

Hydrostatic Drives

. Open circuit design

48 Hydrostatic Drives

. Closed circuit design

Sauer-Danfoss, Ames, IA

Hydrostatic Drives

. Four combinations of pump/motor arrangementbdts can be used – Fixed-displacement pump and motor – Fixed-displacement pump and variable- displacement motor – Variable-dispppplacement pump and fixed- displacement motor – Variable-displacement pump and motor

49 Hydrostatic Drives

. Fixed-displacement pump and motor: – Maximum horsepower, torque, and output shaft speed are fixed – Pump and motor have fixed displacement, so these characteristics cannot be changed

Hydrostatic Drives

. Fixed-displacement pump and variable- displ acement mot or: – Maximum horsepower is fixed – Torque and speed are variable – Due to use of a relief valve, efficiency is lowered – Output shaft rotation may be reversed if the pump is reversible

50 Hydrostatic Drives

. Variable-displacement pump and fixed- displ acement mot or: – Torque output is fixed – Horsepower and output shaft speed are variable – Output shaft rotation may be reversed if pump is reversible

Hydrostatic Drives

. Variable-displacement pump and motor: – Horsepower, torque, output shaft speed are variable – Output shaft direction is reversible – Most versatile of the four pump/motor combinations

51 Hydrostatic Drives

. Hydrostatic drives are typically considered hy dros tati c t ransmi ssi ons wh en b oth th e pump and motor have variable displacement . This combination allows manual or automatic control of torque, speed, and power output

Hydrostatic Drives

. Two different general techniques are used in the construction of hydrostatic transmissions –Integral – Nonintegral

52 Hydrostatic Drives

. Integral construction combines all of the tiititilhitransmission parts into a single housing . Nonintegral construction involves separate pump, motor, and accessories connected by hoses or tube assemblies

Review Question

A(n) _____ cylinder can exert force during bththboth the ext ensi on and ret racti on st rok es.

double-acting

53 Review Question

A(n) _____ is the system component that convertflidts fluid pressure and dfl flow i itnto li near force and movement.

hydraulic cylinder

Review Question

List the three basic configurations used to mountlidtt cylinders to equi pment .

A. Fixed centerline, B. fixed non-centerline, and C. pivoting centerline.

54 Review Question

The three conceptual component groups that make up anyyy hydraulic motor are: A. Rotor, vanes, and eccentric. B. Housing, rotating internal parts, and power output shaft. C. Housing, reciprocating internal parts, and power input shaft. D. Rotating internal parts, power input shaft, and power output shaft.

B. Housing, rotating internal parts, and power output shaft.

Review Question

To vary the displacement of a vane motor, a movable _____ is use d to c hange the s ize o f the pumping chambers.

cam ring

55 Review Question

List the four possible pump/motor arrangements that may b e used with a h yd rost ati c syst em.

A. Both pump and motor have fixed displacements, B. pump has a fixed displacement and the motor a variable displacement, C. pump has a variable displacement and the motor a fixed displacement, and D. both pump and motor have variable displacement.

Review Question

During retraction, what is the effective area of the pi st on of a d oubl e-acting cyli nd er?

The cross-sectional area of the piston minus the cross-sectional area of the rod.

56 Review Question

A cylinder that has externally mounted metal rods h o lding the en ds on the barre l is call ed a(n) _____ cylinder.

tie-rod

Glossary

. Barrel – The component containing the cylinders of an axial piston hydraulic pump. . Clevis mount – A cylinder rod and cap mounting configuration involving a C-shappged casting and a mounting gp pin that allows the cylinder to pivot during extension and retraction.

57 Glossary

. Closed circuit – A hydraulic circuit design in which pump output is returned directly to the pump inlet after passing through a hydraulic motor. The design is commonly used with hydrostatic drive systems.

Glossary

. Cushioning – A des ign f eat ure i n fl uid power cyli nd ers th at reduces fluid flow near the end of the extension or retraction stroke to decelerate piston movement, which avoids both noise and component damage. . Double-acting cylinder – Cylinders that may be powered both on the extension and retraction strokes.

58 Glossary

. Effective piston area – The area of a piston that contributes to the force generated by system pressure. For example, the effective area of a cylinder piston during retraction is the area of the piston minus the cross-sectional area of the piston rod.

Glossary

. Fixed-centerline mount – A cylinder-mounting design in which the load carried by the cylinder rod and piston is supported at the centerline of the cylinder barrel, which is fixed to a machine member.

59 Glossary

. Head – The height of a column of water or other liquid necessary to develop a stated pressure. . Hydrostatic drive – A fluid power drive system using a hydraulic pump and motor to transmit the pppower of a prime mover to the input of a machine. Available in either open- or closed-circuit designs.

Glossary

. Limited-rotation actuator – AttdithtiildAn actuator design that primarily produces rotational movement of one revolution or less. Various designs are available using a rack and pinion, vane, or helical shaft. . Mill cylinder – A hydraulic cylinder constructed of heavy steel for use in industries such as foundries and steel mills.

60 Glossary

. Open circuit – A hydraulic circuit that uses the layout of a basic hydraulic motor circuit with a directional control valve to control motor direction and a reservoir to hold surplus fluid.

Glossary

. Orbiting gerotor motor – A variation of the gerotor motor that uses the internal-toothed gear of the gerotor set as a fixed gear. The external-toothed gear orbits following the internal-toothed gear. This produces higher torque/lower speed output.

61 Glossary

. Parallel circuit – An electrical or fluid power circuit that simultaneously provides multiple paths for the current or fluid to follow as it moves through a circuit.

Glossary

. Pivoting-centerline mount – A clevis or trunnion mounting that allows the cylinder to follow an arc as it powers a machine member. The load remains concentrated on the centerline of the cylinder.

62 Glossary

. Replenishment circuit – A circuit used with closed-loop hydraulic systems that provides makeup fluid to replace any fluid lost from leakage during system operation. . Series circuit – An electrical or fluid pppower circuit that provides only one path for the current or fluid to follow as it moves through the circuit.

Glossary

. Single-acting cylinder – A cylinder design that exerts force only on extension or retraction and depends on some outside force to complete the second movement.

63 Glossary

. Telescoping cylinder – A linear actuator constructed of several nested tubes that can extend a distance equal to several times the actuator’s retracted length. . Threaded-end cylinder – A linear actuator desiggpn in which the cap and head are attached to the barrel of the cylinder by threads.

Glossary

. Tie-rod cylinder – A linear actuator design in which the cap and head components are secured to the barrel of the cylinder by external tie rods that run between those components.

64 Glossary

. Trunnion mount – A cylinder mounting method that places fittings on the sides of cylinders, allowing the cylinder to pivot as it extends and retracts to move a machine member.