Hidráulica Proporcional Basic Level 01

Proportional hydraulics

Learning System for Automation and Communications

Set of overheadtransparencies

Basic level

D.OT-TP701-GB

095061

Order No.: 095061Description: PROP.H.FOLIENDesignation: D.OT-TP701-GBEdition: 8/96Graphics: T. Ocker, B. BöhlandLayout: 29.7.96, M. SchwarzAuthors: F. Ebel

© Copyright by Festo Didactic KG, D-73734 Esslingen, 1996

All rights reserved, including translation rights. No part of this publica-tion may be reproduced or transmitted in any form or by any means,electronic, mechanical, photocopying, or otherwise, without the priorwritten permission of Festo Didactic KG.

This set of overhead transparencies has been designed for the basiclevel technology package TP700. The set of overhead transparenciesand the technology package form part of the Festo Didactic KG Lear-ning System for Automation and Communiations.

Introduction

The 28 overhead transparencies which comprise this set have beendesigned in accordance with dictactic and methodological principles.Each transparency is accompanied by a short explanatory text, whichgives the instructor a brief overview of of the training content coveredby the transparency.

Training contents:

• Fundamentals of proportional hydraulics

• Function and use of proportional hydraulic components

• Electronic components for the actuation of proportional valves

• Comparison with electro-hydraulic control systems

The text sheet includes a full illustration of the transparency, partlysupplemented by additional explanations and designations, which canbe added to the transparency by the instructor in the course of training.

The advantages of this layout are:

• The instructor can expand the transparencies step by step in thecourse of training

• Lessons become more interesting

• The available explanatory texts reduce the amount of preparationrequired by the instructor

701Festo Didactic

Proportional hydraulic system . . . . . . . . . . . . . . . . . . . . . Transparency 1Table of contents

Mobile hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 2

Proportional valve activation . . . . . . . . . . . . . . . . . . . . . . Transparency 3

Honing machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 4

Electro-hydraulics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 5

Proportional hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 6

Electro-mechanical transducers . . . . . . . . . . . . . . . . . . . Transparency 7

D.C. switching solenoid . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 8

Proportional solenoid with intermediate ring . . . . . . . . . . Transparency 9

Proportional solenoid, stroke-controlled . . . . . . . . . . . Transparency 10

Proportional solenoid, force-controlled . . . . . . . . . . . . Transparency 11

Proportional solenoid, components . . . . . . . . . . . . . . . Transparency 12

Electronic activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 13

Proportional amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 14

Ramp shaper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 15

Minimum current – Maximum current . . . . . . . . . . . . . Transparency 16

Output stage ( V/I converter) . . . . . . . . . . . . . . . . . . . . . Transparency 17

Pulse duration modulation . . . . . . . . . . . . . . . . . . . . . . . Transparency 18

Hysteresis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 19

Flow characteristic curves . . . . . . . . . . . . . . . . . . . . . . . Transparency 20

Control edge patterns . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 21

Piston opening ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 22

Piston overlap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 23

Pressure relief valve, piloted . . . . . . . . . . . . . . . . . . . . . Transparency 24

Pressure regulating valve, piloted . . . . . . . . . . . . . . . . Transparency 25

Flow control valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 26

4/3-way valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 27

4/3-way valve, piloted . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 28

Festo Didactic701 Festo Didactic

701Festo Didactic

Proportional hydraulic systemTitle

• Classification into signal control section and power section.Guide

• Signal processing has been further enhanced by the provision ofsetpoint value and current signal conversion.

• The multiple function of proportional valves reduces the number ofhydraulic components to a minimum.

• Proportional solenoids form the interface between the signal controlsection and the power section.

Signalprocessing,

control

Power supplyPower section

Proportionalvalves

ActuatorsSetpoint

generatorSignal

amplificationSignalinput

Power supply Power section~

PLCp

A B

P T

PM

1 Proportional hydraulics Festo Didactic

701-01-GB

Mobile hydraulicsTitle

• Origins of mobile hydraulics. Long hose connections betweencontrol valves and hydraulic drive components.

Guide

• Ratio of hand lever movement to piston deflection is approximatelyproportional.

• Control pattern: High-precision controllability at start of hand leverdisplacement, large flow rate change during hand lever movementsat end deflection.

• In this instance, flow is not released until end deflection due to thepositive piston overlap.

701-02-GB

P AT B

BA

Flowrate [Q]

High-precision controllability

Pistondeflection

Hand lever movement

A

B

B

A

Piston overlap


Proportional valve activationTitle

• Setpoint values are converted into magnetic flux and amplified.Guide

• By means of the proportional solenoid, magnetic flux is convertedinto piston deflection within the hydraulic valve.

• Actuation of proportional directional, pressure and flow control valves.

701-03-GB

3

Proportional amplifier Proportional solenoid

Directional valves

Pressure valves

Flow control

Proportional hydraulics Festo Didactic

Honing machineTitle

• Typical machine tool employing a proportional hydraulic controlsystem.

Guide

• Continuous path control on machine tools: Controlling of path,speed and acceleration.

• Smooth transition of upward and downward stroke of honingmachine in accordance with time function.

4

701-04-GB

Time

Cyl. stroke

advanced 1

retracted 0


Electro-hydraulicsTitle

• Example for conventional electro-hydraulics:Control of velocity stages.

Guide

• Use of parallel switching flow control valve for control of velocitystages.

• Digital switching characteristics: only preset flow rates can beinvoked (example: flow control valve).

• Extensive hydraulic circuit requirement.

701-05-GB

5

1 0

1 0

1 0

1 0

1 0

1 1 0 0 0

0 00 0 1

00 0

0 0 0 00

Y1 Y2

Y3

Y4

Y4

Y1

Y2

Y3

Time [t]

0 2 31

PM

Cyl

inde

r st

roke

1

3

2

0


Proportional hydraulicsTitle

• Example for proportional hydraulics:Control of velocity stages.

Guide

• Hydraulic circuit requirement considerably reduced, electrical signalcontrol section extended.

• Additional requirements for commissioning: Setting of setpointvalues and ramp functions.

• Analogue valve cross section openings according to setpoint valuesand thus different flow range, i.e. actuator speeds.

• Flexibility thanks to electrical control, e. g: an additional velocitystage requires only one additional setpoint value.

701-06-GB

6

Y1 Y2

Y1 Y2

IY1

IY2

IY1IY2

Time [t]

3

0

2

Time [t]

P

4

M

Cylinderstroke

0 3 41 2

Current

1


Electro-mechanical transducersTitle

• Proportional solenoid: Further development of switching solenoid.The magnetic flux causes a force which remains constantthroughout the stroke. The force acts only in one direction. Theextent of the magnetic force is proportional to the magnetic flux.

Guide

• Due to its force, the servo drive of the proportional solenoid isparticularly suitable for the direct actuation of standard proportionalvalves.

• Plunger coil: Also an electro-dynamic principle, whereby a force actson a current carrying conductor in the magnetic field. Depending onthe direction of current the plunger coil is deflected up or down.

• Torque motor: The effects of the permanent and electro magnetsare superimposed. The magnetic force causes a torque to the rightor the left.

• The servo drive, plunger coil and torque motor have a high naturalfrequency, which makes them suitable for the indirect actuation ofhighly dynamic proportional and servo valves.

701-07-GB

7

F x x

5 - 40

20 - 1000

0.5 - 6

10 - 150

0.2 - 5

8 - 80

1 - 7

100 - 200

0.02 - 4

2 - 40

1 - 2

100 - 300

N N

S S

Power consumption

Working stroke

Linear deviation

Critical frequency

Proportional soleonid Torque motorPlunger coil

[W]

[Nmm]

(%)

[Hz]


D.C. switching solenoidTitle

• Magnetic field lines of a coil.Guide

• Existence of a homogenous magnetic field within a coil withoutmagnet core or armature.

• Radial air gap and axial air gap form different “resistances” in themagnetic field.

• The magnetic force acts on the armature mainly via the radial airgap, since in this case the gap between the core and armatureremains small.

701-08-GB

8

Magnetic field lines Axial air gap

Radial air gap

Homogenous magnetic field


Proportional solenoid with intermediate ringTitle

• Different magnetic forces act on the armature via the axial air gap.Guide

• Reducing the magnetic field lines via the radial air gap by means ofinstalling a non-magnetisable intermediate ring.

• The new distribution of the magnetic field line leads to a virtuallyconstant magnetic force pattern within the working stroke range.

• 1 = Magnetic force characteristic in the axial air gap2 = Magnetic force characteristic in the radial air gap3 = Summation characteristic curve

9

1 = Magnetic force characteristic in the axialair gap

2 = Magnetic force characteristic in the radialair gap

3 = Summation characteristic curve

Working strokea b ≈ 1mm c

32

1

Axial air gap

Radialair gap

Magneticforce [N]

Pistonposition

b

c

a

0

3

6

701-09-GB


Proportional solenoid, stroke controlledTitle

• The solenoid force is proportional to the electrical input signal.Guide

• Poppet principle: The valve cone is pressed against the valve seatvia a spring; the valve opens as soon as the hydraulic force on thevalve cone exceeds the pilot force, whereby the entire spring/plunger system is moved back.

• Spool principle: the valve piston is pushed against the spring, thestroke movement ceases when the magnetic force and the springforce are in equilibrium.

• Force/stroke characteristic curves:Magnetic force with specified current values in relation to plungerposition; characteristic curve of a pressure loaded spring.

Working stroke

Characteristicspring curve

Poppet principle

Spool principle

Idle stroke

Characteristic force/stroke curves

Magneticforce [N]

Pistonposition

0

3

6

701-10-GB


Proportional solenoid, force controlledTitle

• The solenoid force is proportional to the electrical input signal.Guide

• Only poppet type valves can be operated via force controlledsolenoids.

• This valve is used as a pilot pressure valve for directional orpressure control valves because of the reduced flow rates.

Poppet principle (only)

F ~ I

P

T

Force/current characteristic curve

Magnetic flux I [A]

MagneticforceF [N]

P

T

701-11-GB


Proportional solenoid, componentsTitle

• Construction of proportional solenoids.Guide

• D.C. solenoid group.

• Representation of the most important components of aproportional solenoid.

• Electro-mechanical transducer: the electrical input signal isconverted into a mechanical output signal.

701-12-GB

12

Exciting coil

Core magnet

Guide rod (stem)Plain bearing

Stop/Guide disc

Electrical connection

Housing

Compensatingspring

Non-magnetisableinner ring

Control cone

Barrel magnet

Armature

Venting screw


Electronic activationTitle

• Control stages of a proportional amplifier for magnetic fluxgeneration.

Guide

• The input signal is set by means of ramp time, minimum ormaximum current and pulse duration modulation.

• Both the amplification of the signal and the conversion by meansof a V/I converter take place during the output stage.

• Proportional solenoid valves are to be actuated via an adjustableD.C. current of 0 to 800 mA.

701-13-GB

13

Setpointspecification

Settingof

amplifiercharacteristic

Pulse-durationmodulation V/I-converter Proportional

valveRampsetting

Y1 Y2

A B

P TV

I

VI


Proportional amplifierTitle

• Control panel of a setpoint and amplifier card.Guide

• W1 - W8: Input of up to 8 setpoint values.

• R1 - R4: Setting of ramps. TIME = Ramp time.

• IA - IB: Setting of initial, jump and maximum current.

• 24V, 0V: Supply voltage.

• Liquid crystal display for representation of all parameters.

701-14-GB

14

I2

I3

I1

W2W3

W4

W5

W6

W7W8OUTD/E

FUNCTION

R4

TIME

R3

R2R1 W1

+24V+24V

0V 0V

OUT

CONTRAST

W2

W1

B

A

IA BASICIB BASIC

IA JUMP

IB JUMP

IA MAXIB MAX

DITHERFREQ.CONTRAST

D/EINT W2

W2

INT W1

W1IB

IAFUNCTION

+24V+24V

0V 0V

INT W1 OE A

INT W2 OE B


Ramp shaperTitle

• Left: Signal transmission in switching hydraulics.Right: Signal transmission in proportional hydraulics with ramp shaper.

Guide

• Use of ramps for adjustable acceleration or delay of hydraulic drivecomponents.

• Angular setting: The ramp angle determines the adjustable speed ofthe valve piston.

• Elimination of pressure peaks and switching impacts in the hydraulicsystem.

• Displacement positions:0: Retracted end position1: Acceleration completed2: Delay initiated (signal generator)3: Forward end position

701-15-GB

15

Cylinder

Inputsignal

Controlsignal

Signal generator

Signal generator

0

1

Displacement

Time [t]

Time [t]

0

1

0%

100%

Displacement

Time [t]

Time [t]

Time [t]

0

2

0

3 3

1

t3

t3

t1

t1

t0 t2t0

t3t0 t0

t0

t2

Y1

Y1

t2

Y1 Y2

Y1 Y2

0 31 20 3


Minimum current – Maximum currentTitle

• Setting of minimum and maximum current for adjustment ofproportional directional control valve to flow rate of hydraulic pump.

Guide

• Minimum current for adjustment of jump current to control edge.

• Maximum current or adjustment of maximum cross section of theopening in relation to flow rate QPump.

• A linear characteristic curve runs between minimum and maximumcurrent.

701-16-GB

16

Amplifiercharacteristic

Imax

Imin

Setting

∆Q ≈ 0

∆s = min. ∆s = max.

Setting

I[mA]

0 10 VoltSetpoint value

800

∆Q ≈ max.


Output stage (V/I converter)Title

• The setpoint voltage is converted into a magnetic flux in the outputstage.

Guide

• Closed-loop control of magnetic flux through comparison of setpointvalue and actual value on the measuring shunt RM.

• The closed control loop is created by means of connecting theactual value via the feedback resistor RR.

• The closed control loop eliminates the effects resulting fromoperating voltage fluctuations and/or the effects resulting fromproportional solenoid heating.

• The solenoid coil has an ohmic resistor RS and an inductive resistorLS.

701-17-GB

17

RS

LS

RS

LS

VVVI

R I

RR

RM

Power supply voltage

Solenoid coil

Input resistance

Input signal

Coil: Ohmic resistorCoil: Inductive resistor

Feedback resistor

Measuring shunt


Pulse duration modulationTitle

• Recording of pulsed voltage signals and the associated magneticflux.

Guide

• The output voltage is maintained at a constant level. The switch-on/switch-off ratio (pulse duration) within a time period T influences thesize of the effective magnetic flux.

• Clean-switching operations prevent excessive heating of the outputstage and power dissipation is kept to a minimum.

• An oscillating output current is obtained thanks to pulse durationmodulation. Sliding friction prevails at the plunger thanks to thisdither effect and the hysteresis is improved.

701-18-GB

18

= Duty cycle

= Effectivemagnetising current

Solenoidvoltage

T

T

T

V

Time

Time

Time

24 V

0

V24 V

0

V24 V

0

Ieff

Ieff

Ieff


HysteresisTitle

• The friction of the valve piston spool causes a resistance todirectional movement.

Guide

• Hysteresis: Differential current during approach of a pressure orflow rate value from different directions.

• Pulse duration modulation: Reduction of hysteresis by means ofcontinuous slight oscillating movement of the piston spool (slidingfriction).

• Avoidance of pressure peaks in the hydraulic system.

701-19-GB

19

∆I

Pulse durationmodulation

p [bar]

50

40

30

20

10

100 200 300 400 500 600 7000 I [mA]800


Flow characteristic curvesTitle

• Representation of control piston with different control notches;Representation of the corresponding flow characteristic curves.

Guide

• Delta control edge pattern: Precision controllability for small volu-metric flow rates, clear changes within the range of large volumetricflow rates.

• The stroke travel of a piston with control notches corresponds to themaximum length of the notch opening.

701-20-GB

20

Q[l/min] 8

6

4

2

100 400 700 I [mA]0

Q[l/min] 8

6

4

2

100 400 700 I [mA]0


Control edge patternsTitle

• Control edge pattern for the purpose of determining the flowbehaviour of the valve.

Guide

• The adjustment of flow behaviour is linear, progressive, degressiveor generally according to the task.

• Number of precision control openings on the periphery of the controlpiston depending on valve function.

• The sleeve system is easier to produce in terms of productiontechnology.

701-21-GB


Piston opening ratioTitle

• Example: Actuation of a 2:1 cylinder.Guide

• The ratio of the valve flow cross sections is adjusted to the cylinderinlet and outlet by means of control edge pattern.

701-22-GB

22

Cylinder 2:1

T P T

A B


Piston overlapTitle

• Representation of positive, negative and zero overlap.Guide

• Alternative designations: Overlap, underlap and zero intersection.

• The opening of the valve port is dependent on the notched openingin relation to the control edge.

• The flow rate is also adjusted by means of the throttle opening ratioof the control piston. The number of radially configured notches onthe control piston.

701-23-GB

23

= 0

> 0

< 0

positive

zero

negative

X X

X X

X X

QL

QL

QL

QA

QB

QA

QB

QA

QB


Pressure relief valve, pilotedTitle

• Sectional view of a pressure relief valve.Guide

• The mode of operation corresponds to that of a conventional,piloted pressure relief valve.

• Piloted stage: the force set for the proportional solenoid is trans-ferred to the pilot poppet via the spring.

• As soon as the pressure acting on the pilot valve exceeds the valueset, the poppet valve opens. The venting control flow generates apressure drop at the main stage, whereby this opens.

701-24-GB

24

P

TP

T Y

Y

p [bar]

4

3

2

1

20 400 I [mA]

5


Pressure regulating valve, pilotedTitle

• Sectional view of a piloted pressure regulating valve.Guide

• Reduction of system pressure to a specific value.

• Application for subranges within a hydraulic system.

701-25-GB

25

P

A

Y

A

P Y


Flow control valveTitle

• Sectional view of a flow control valve.Guide

• Normal position: all ports are closed.

• Depending on the piston deflection, control cross sections (holes inthe piston, control sleeve) and thus the flow are changed.

701-26-GB

26

P T

A BFlow characteristic curve

I [mA]

Q

2

4

6

8

200100 300 400 5000 600

lmin[ ]

P T

A B


4/3-way valveTitle

• Essential functional components: Proportional solenoids, main spool,reset spring.

Guide

• Multiple functions: Directional control, speed control, hydraulicclamping of power components (throttle opening ratio).

701-27-GB

27

T B P A

P T

A B


4/3-way valve, pilotedTitle

• Pressure relief valves for pilot control of a 4/3 proportionaldirectional control valve.

Guide

• Electrical signal to one of the two proportional solenoids increasesthe pressure inside the control chamber of the main spool to aspecified value (relief pressure).

• The control piston is moved up to the equilibrium position with theopposing spring action.

• High control force due to minimum control pressure of 25 bareliminates sensitivity to disturbance factors. This is howeverassociated with continuous control oil consumption.

• Without an electrical signal, the control piston is centred by meansof the springs.

701-28-GB

28

Actuation B Actuation A

P T

A B

P

T

P

T

AT BP


Hidráulica Proporcional Basic Level 01

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