Electrohydraulics Basic Level - festo-didactic.com · Hydraulic linear cylinder (Storz Hydrauliksysteme GmbH) and hydraulic motor (Sauer-Danfoss GmbH & Co) Hydraulic systems are used

Textbook TP 601

Festo Didactic

093611 en

ElectrohydraulicsBasic Level

093611_cover_textbook_tp601_en.indd 1 01.04.2005 08:41:39

Order No.: 093611

Edition: 03/2006

Authors: C. Löffler, D. Merkle, G. Prede, K. Rupp, D. Scholz

Graphics: Doris Schwarzenberger

Layout: 30.05.2006, Beatrice Huber

© Festo Didactic GmbH & Co. KG, 73770 Denkendorf, Germany, 2006

Internet: www.festo-didactic.com

e-mail: [email protected]

The copying, distribution and utilization of this document as well as the

communication of its contents to others without expressed authorization is

prohibited. Offenders will be held liable for the payment of damages. All rights

reserved, in particular the right to carry out patent, utility model or ornamental

design registration.

© Festo Didactic GmbH & Co. KG • TP 601 3

Preface______________________________________________________________ 5

1. Introduction___________________________________________________ 7

1.1 Areas of application of electrohydraulics ____________________________ 7

1.2 Basic control engineering terms ___________________________________ 9

1.3 Hydraulic and electrohydraulic control systems _____________________ 15

1.4 Advantages of electrohydraulic control systems _____________________ 21

2. Fundamentals of electrical technology____________________________ 23

2.1 Direct current and alternating current _____________________________ 23

2.2 Ohm's Law ___________________________________________________ 24

2.3 Mode of operation of a solenoid__________________________________ 26

2.4 Mode of operation of a capacitor _________________________________ 28

2.5 Mode of operation of a diode ____________________________________ 29

2.6 Measurement in electrical circuits ________________________________ 30

3. Components and assemblies in the electrical signal control section ___ 35

3.1 Power supply unit _____________________________________________ 35

3.2 Push button and control switches ________________________________ 36

3.3 Sensors for measuring displacement and pressure___________________ 38

3.4 Relays and contactors __________________________________________ 48

3.5 Programmable logic controllers __________________________________ 53

3.6 Overall structure of the signal control section _______________________ 54

4. Solenoid actuated directional control valves _______________________ 57

4.1 Exercises ____________________________________________________ 57

4.2 Design and mode of operation ___________________________________ 59

4.3 Designs and hydraulic performance data___________________________ 77

4.4 Performance data of solenoid coils _______________________________ 90

4.5 Electrical connection of solenoid coils _____________________________ 93

5. Design of an electrohydraulic control system ______________________ 97

5.1 Procedure for the development of a control system __________________ 97

5.2 Procedure for the planning of a control system ______________________ 99

5.3 Application example: Design of a sawing machine __________________ 103

5.4 Procedure for the realisation of the control system__________________ 122

Contents

Contents

4 © Festo Didactic GmbH & Co. KG • TP 601

6. Documentation of an electrohydraulic control system ______________ 127

6.1 Function diagram _____________________________________________ 128

6.2 Sequence table ______________________________________________ 137

6.3 GRAFCET____________________________________________________ 139

6.4 Hydraulic circuit diagram ______________________________________ 162

6.5 Electrical circuit diagram _______________________________________ 176

6.6 Terminal connection diagram ___________________________________ 187

7. Safety measures for electrohydraulic control systems ______________ 197

7.1 Dangers and protective measures _______________________________ 197

7.2 Effect of electric current on the human body _______________________ 198

7.3 Measures to protect against accidents with electric current___________ 201

7.4 Control panel and indicating elements____________________________ 202

7.5 Protecting electrical equipment against environmental impact ________ 206

7.6 Safety recommendations for electro-hydraulic systems ______________ 208

8. Relay control systems ________________________________________ 209

8.1 Use of relay control systems in electrohydraulics ___________________ 209

8.2 Direct and indirect actuation____________________________________ 209

8.3 Logic operations _____________________________________________ 213

8.4 Signal storage _______________________________________________ 216

8.5 Delay_______________________________________________________ 222

8.6 Sequence control with signal storage via double solenoid valves ______ 224

8.7 Circuit for evaluating control elements____________________________ 235

8.8 Sequence control system for a sawing machine ____________________ 238

Index _____________________________________________________________ 265

Standards _________________________________________________________ 273


Electrohydraulics are in use in numerous areas of industrial automation. To give a

few examples, woodworking machines, machine tools, process engineering plants,

presses, plastics processing machines and conveyor systems worldwide are

operated using electrohydraulic control systems. However, electrohydraulic control

systems are also in use in a wide variety of ways such as in mobile hydraulics which

include agricultural vehicles, road construction or street cleansing.

Changing requirements and technical development have distinctly changed the

appearance of control systems. The relay in the signal control section increasingly

has been replaced by programmable logic controllers in many areas of application in

order to meet the increased need for flexibility. In the power section too, advanced

electrohydraulic control systems feature new concepts adapted to the needs of

industrial practice. To mention just a few keywords such as control block, bus

networks and proportional hydraulics. The close interaction of fluid power

engineering with microelectronics, sensors and information technology leads to

numerous innovations in the area of oil-hydraulic drives and control systems. These

in turn open up new fields of application to electrohydraulics with more challenging

tasks in process control.

As an introduction to the subject, the textbook first of all explains the design and

mode of operation of the components required for the construction of an

electrohydraulic control system. The following chapters describe the procedure for

the planning, design and realisation of electrohydraulic control systems, using fully

detailed examples.

All readers of this book are invited to contribute with tips, suggestions and

constructive criticism in order to improve the book.

March 2006 The authors

Preface



Hydraulics involves the use of hydraulic fluids. Hydraulic fluids are most commonly

used to perform mechanical work. Mechanical work is necessary in order to carry out

movements and generate forces. The function of hydraulic drives is to convert the

energy stored in hydraulic fluid into kinetic energy.

The following are used as hydraulic drives:

• Cylinders (linear drives) for the generation of straight-linear movements ,

• Motors and semi-rotary actuators drives (rotary drives) to generate rotary

movements.

Hydraulic linear cylinder (Storz Hydrauliksysteme GmbH) and hydraulic motor (Sauer-Danfoss GmbH & Co)

Hydraulic systems are used if high performance levels, excellent heat dissipation,

regular movement, high switching dynamics or extremely high forces are required.

Applications of electrohydraulics can be found both in stationary and mobile

hydraulics. Characteristic of electrohydraulics is the receiving, processing and

output of signals. The valves forming the interface to the power section are also

solenoid actuated.

Important branches of electrohydraulics are:

• Machine building, where electrohydraulic system for example are used to feed

machine tools, for the generation of force for presses or in injection moulding

machine for plastics processing

• Automotive engineering, where electrohydraulic systems are the preferred

option for the actuation of construction machinery or also for the control of

steering mechanisms on agricultural machinery

• Steel and power station construction. Here, electrohydraulic systems are used

for theatre technics, lifting platforms, for the control of locks, weir gates and

movable bridges

1. Introduction

1.1

Areas of application of

electrohydraulics

1. Introduction


• Aircraft construction, where for example the actuation of the landing flaps and

rudders is realised electrohydraulically

• Ship building, where for example the rudder or the cargo cranes are controlled

electrohydraulically

In the case of modern CNC controlled machine tools, tools and workpieces are

clamped hydraulically. Feed functions and spindle drives can also be hydraulically

realised.

Rotary indexing machine

Application example

1. Introduction


Hydraulic drives can only do work usefully if their motions are precise and carried

out at the right time and in the right sequence. Coordinating the sequence of motion

is the task of the control system.

Control engineering deals with the design and structure of control systems. The

following section covers the basic terms used in control engineering.

DIN 19226, Part 1 defines the term “control“ as follows:

Controlling – open loop control – is that process taking place in a system whereby

one or more variables in the form of input variables exert influence on other

variables in the form of output variables by reason of the laws which characterize

the system. The distinguishing feature of open loop control is the open sequence of

action via the individual transfer elements or the control chain.

The term open loop control is widely used not only for the process of controlling but

also for the plant as a whole.

In an assembly device, locating holes on sub-bases for valves are sealed with

blanking plugs. The closing process is triggered via the operation of a pushbutton at

the workplace. When the pushbutton is released, the piston retracts to the retracted

end position.

In this control, the position of the pushbutton (pushed, not pushed) is the input

variable. The position of the pressing cylinder is the output variable. The loop is

open because the output variable (position of the cylinder) has no influence on the

input variable (position of the pushbutton).

1.2

Basic control engineering

terms

Control

Application example

1. Introduction


Assembly device for fitting caps in locating holes

Controls must evaluate and process information (for example, pushbutton pressed

or not pressed). The information is represented by signals. A signal is a physical

variable, for example

• The pressure at a particular point in a hydraulic system

• The voltage at a particular point in an electrical circuit

1. Introduction


1

0

2

3

4

5

MPa

7

Pressure

Time

Signal and information: Signal/physical variable

1

0

2

3

4

5

6

7

01

2 3 4567

8

Pointer position

Time

Signal and information: Information, analogue

PressureMPa

1

0

2

3

4

56

7 3

Display

Time

Signal and information: Information, digital

1. Introduction


No

Yes

Pressure

Time

Supplypressure

0

1

Signal and information: Information, binary

A signal is the representation of information The representation is by means of the

value or value pattern of the physical variable. The different signal types are

described in DIN 19226, Part 5.

An analogue signal is a signal in which information is assigned point by point to a

continuous value pattern of the signal parameter.

In the case of a pressure gauge, each pressure value (information parameter) is

assigned a particular display value (= information). If the signal rises or falls, the

information changes continuously.

A digital signal is a signal with a finite number of value ranges of the information

parameter. Each value range is assigned a specific item of information.

A pressure measuring system with a digital display shows the pressure in

increments of 1 MPa. There are 8 possible display values (0 to 7 MPa) for a pressure

range of 7 MPa. That is, there eight possible value ranges for the information

parameter. If the signal rises or falls, the information changes in increments.

A binary signal is a digital signal with only two value ranges for the information

parameter. These are normally designated 0 and 1.

A control lamp indicates whether a hydraulic system is being correctly supplied with

hydraulic fluid. If the supply pressure (= signal) is below 5 MPa, the control lamp is

off (0 status). If the pressure is above 5 MPa, the control lamp is on (1 status).

Analogue signal

Application example

Digital signal

Application example

Binary signal

Application example

1. Introduction


Controllers can be divided into different categories according to the type of

information representation, into analogue, digital and binary controllers.

Controllers

Analoguecontrollers

Digitalcontrollers

Binarycontrollers

Classification of controllers by type of information representation

A logic controller generates output signals through logical association of input

signals.

The assembly device for sub-bases is extended so that it can be operated from two

positions. The two output signals are linked. The piston rod advances if either

pushbutton 1 or 2 is pressed or if both are pressed.

A sequence controller is characterized by its step by step operation. The next step

can only be carried out when certain criteria are met.

Drilling station. The first step is clamping of the workpiece. As soon as the piston rod

of the clamping cylinder has reached the forward end position, this step has been

completed. The second step is to advance the drill. When this motion has been

completed (piston rod of drill feed cylinder in forward end position), the third step is

carried out, etc.

Classification of controllers

by type of information

representation

Logic controller

Application example

Sequence controller

Application example

1. Introduction


A control system can be divided into the functions signal input, signal control, signal

output and command execution. The mutual influence of these functions is shown

by the signal flow diagram.

• Signals from the signal input are logically associated (signal control). Signals for

signal input and signal process are low power signals. Both functions are part of

the signal control section.

• At the signal output stage, signals are amplified from low power to higher power.

Signal output forms the link between the signal control section and the power

section.

• Command execution takes place at a high power level – that is, in order to move

heavy loads (e.g. a lock gate) or to exert a high force (such as for a press).

Command execution belongs to the power section of a control system.

Command execution

Signal output

Signal processing

Signal input

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ign

al

con

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Signal flow in a control system

The components in the circuit diagram of a purely hydraulic control system are

arranged so that the signal flow is clear. Bottom up: input elements (such as

manually operated valves), logical association elements (such as shuttle valves),

signal output elements (power valves, such as 4/2-way valves) and finally command

execution (such as cylinders).

Signal flow in a control

system

1. Introduction


Hydraulic and electrohydraulic control systems both exhibit a hydraulic power

section. However, the signal control section is constructed differently.

• In the case of hydraulic control systems, this section is mainly carried out

manually. It is rare for the signal control to be effected by means of a hydraulic

circuit, which then comprises for example shuttle valves.

• In the case of an electrohydraulic control system, the signal control section is

constructed using electrical components, which include for example electrical

input keys, proximity sensors, pressure switches, relays or a programmable logic

controller.

In the case of both types of control, the directional control valves form the inteface

between the signal control section and the hydraulic power section.

Final control elementsDirectional control valves

Signal flow

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po

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ydra

uli

c si

gn

al

con

tro

l se

ctio

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Signal output

Signal processing

Signal input

Hydraulic components

Command execution

Processing elementsDirectional control valvesShuttle valvesPressure control valves

Input elementsDirectional control valves(mechanically operated)Directional control valves(manually operated)

Power componentCylinderSwivel cylinder

motorsOptical displaysHydraulic

Signal flow and components of a hydraulic control system

1.3

Hydraulic and

electrohydraulic control

systems

1. Introduction


Ele

ctri

cal

sig

na

l co

ntr

ol

sect

ion

Signal output

Signal processing

Signal input

Signal flow

Command execution

Hyd

rau

lic

po

we

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c tio

n

Electrohcomponents

ydraulic

Final contol elementsElectropneumaticallyoperated directionalcontrol valves

Processing elementsRelaysContactorsProgrammable logiccontrollers (PLCs)

Input elementsPushbuttonsControl switchesLimit switchesReed switchesInd. proximity sensorsCap. proximity switchesLight barriersPressure-actuated switches

Power componentsCylinderSwivel cylinder

motorsOptical displaysHydraulic

Signal flow and components of an electrohydraulic control system

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Electrohydraulics Basic Level - festo-didactic.com · Hydraulic linear cylinder (Storz Hydrauliksysteme GmbH) and hydraulic motor (Sauer-Danfoss GmbH & Co) Hydraulic systems are used