cnc machine training report

1. TRAINING REPORT
ON
CNC MACHINE UNDERTAKEN
HELD AT
PRABHUSHILLA ENGINEERING
PRIVATE LIMITED, NOIDA
Submitted to: = Mr ……………
Submitted By: = Deepak Kumar Prajapati
Roll No.: = 1319340043
Department: = Mechanical
Institute: = UCER, Gr.Noida

2. PREFACE
ACKNOWLEDGEMENT
DECLERATION
PORTFOLIO
INTRODUCTION
CNC (Computerized numerical control)
Advantages of cnc machine
CNC systems
Configuration of cnc system
Parts of cnc system
Types of cnc system
Position feedback
Types of position feedback
Open loop positioning

3. Closed loop positioning
Function of CNC MACHINE
1. PROGRAM
2. MCP (machine control panel)
3. Processing equipment
Various types of mode in MCP
1. continuous mode
2. incremental mode
3. Automatic mode
4. Zig switch mode
5. Block by block mode
6. Reference mode
7. MDI mode (manual data input)
8. Input mode

4. 9. Output mode
INTERFACING
DIAGNOSTICS
MACHINE DATA
PLC (programmable logic controller)
MONITORING
OPERATIONAL PANEL
COMPENSATIONS FOR MACHINE ACCURACY

5. PREFACE
Practical training is also very important aspect in technical course.
There is so many vast differences between theoretical knowledge and
actual practical implication.
Thus Practical training helps individuals of know he actual uses and
impactionof what he has gained from theoretical knowledge.The
theoretical knowledge and classroom discussionis not enoughfor a
technical student now, for the knowledge of practical viewpoints,
problems,opportunities and situationof industrial units practical
studies it necessary.
So as the students of 6th SEM,B.Tech. We also get a valuable
opportunities to learn the practically ofthe theories,which learn.
We have triedto collect all the necessary informationand tried
to prepare this report withthe best of our knowledge and ability.

6. Acknowledgement
The visit/training industry is a part of our study as impliedby AKTU
Lucknow.
We are heartily grateful to all the executives ofPRABHUSHILLA
ENGINEERINGPRIVATE LIMITED.For developing their valuable time
and providing unnecessary informationregarding company and its
management.
Our special Thanks Mr. AMARJEET SINGH and Mr. PARAS SIR who
have made a great effort for making the training program smoothand
easy going.
We must also convey our special thanks to the sir and the Director for
giving us this wider horizon ofsphere of knowledge and finding time
for reading and commenting aportionof the manuscript.
THANK YOU

7. DICLARATION
We the undersigned, Deepak Kumar prajapati, the students
of united college of engineering and research hereby declare
that this report in our own work carried out under
supervision and guidance of managers.
Date...
Place...
SIGN of student
................................
Deepak Kumar prajapati

8. Portfolio
Name of the company: Prabhushilla engineering private ltd.
Established: 2005
Chairman: Rajesh Gupta
Working hours: 8:00 hours and overtime total 12:00
NO. Of members: 240
Accounting Year: 1st April to 31th march

9. COMPUTERIZED
NUMERICAL
CONTROLLED (CNC)
MACHINES
Development of computerized numerical co
ntrolled (CNC) machines is an outstanding
contribution to the
manufacturing industries.It has made possible t
he automation of themachining process with fle
xibilityto handle small to medium batch of qua
ntities in part production.Initially, the CNC
technology was applied on basic metal cutting
machine like lathes, milling machines, etc. Later,
to increase the flexibility of the
machines in handling a variety of components
and to finish them in a single setup on the same
machine, CNC machines capable of performing
multiple operations
were developed. To start with, this
concept was applied to develop a CNC machining
centre for machining prismatic componentscombining
operationslike milling, drilling, boring and taping.
Further, the concept of multi-operationswas also
extended for machining cylindrical components, which
led to the development of turning centers.

10. (ADVANTAGES OF CNC
MACHINE)
 Higher flexibility
 Increased productivity
 Consistent quality
 Reduced scrap rate
 Reliable operation
 Reduced non productive time
 Reduced manpower
 Shortercycle time
 High accuracy
 Reduced lead time
 Just in time (JIT) manufacture
 Automatic material handling
 Lesser floor space
 Increased operation safety
 Machining of advanced material
CNCSYSTEMS
INTRODUCTION
Numerical control (NC) is a method employed for
controlling the motions of a machine tool slide and

11. its auxiliary functions with input in the form of
numerical data. A computernumerical control(CNC) is
a microprocessor-based system to store and process the
data for the control of slide motions and auxiliary
functions of the machine tools. The CNC system is
the heart and brain of a CNC machine which enables
the operation of various machine members such as
slides, spindles, etc. as per the sequence programmed
into it, dependingon the machining operations. The
main advantage of a CNC system lies in the fact
that the skills of the operator hitherto required in the
operation of a conventional machine is removed and the
part production is made automatic. The CNC systems
are constructedwith a NC unit integrated with a
programmable logic controller(PLC) and sometimes
with an additional external PLC (non-integrated). The
NC controlsthe spindlemovement and the speeds and
feeds in machining. It calculatesthe traversing path of
the axes as defined by the inputs. The PLC controlsthe
peripheral actuatingelements of the machine such as
solenoids, relay coils, etc. Working together, the NC
and PLC enablethe machine tool to operate
automatically. Positioning and part accuracy depend on
the CNC system's computercontrol algorithms, the
system resolutionand the basic mechanical machine
accuracy. Control algorithm may cause errors while
computing, which will reflect during contouring, but
they are very negligible. Though this does not
cause point to point positioning error, but when
mechanical machine inaccuracies are present, it will

12. result in poorer part accuracy. This chaptergives an
overview of the configuration of the CNC system,
interfacing and introduction to PLC programming.
CONFIGURATIONOFTHECNCSYSTEM
Shows a schematic diagram of the working
principle of a NC axis of a CNC machine and the
interface of a CNC control
CNCsystem
Schematic diagram of a CNC machine tool A CNC
system basically consists of the following:
Central processing unit (CPU)
Servo-control unit
Operatorcontrol panel

13. Machine control panel
Other peripheral device
Programmable logic controller(PLC)
Fig.2
Gives the typical numerical controlconfiguration of
Hinumerik 3100 CNC system
CentralProcessingUnit(CPU)
The CPU is the heart and brain of a CNC system.
It accepts the information stored in the memory as
part program. This data is decodedand transformed into
specific position control and velocity control signals.
It also oversees the movement of the control axis
or spindle whenever this does not match the
programmed values, a corrective action is taken. All
the compensations required for machine accuracy (like
lead screw pitch error, tool wear

14. out, backlash, etc.) are calculated by the CPU d
epending upon the corresponding inputs madea
vailable to the system. The same will be taken care
of during the generation of control signals for the
axis movement. Also, some safety checks are built into
the system through this unit and the CPU unit will
provide continuousnecessary corrective actions.
Whenever the situation goes beyond control of the
CPU, it takes the final action of shutting down
the system in turn the machine.
SpeedControlUnit
This unit acts in unison with the CPU for the movement
of the machine axes. The CPU sends the controlsignals
generated for the movement of the axis to the servo
control unit and the servo control unit convert
these signals into the suitable digital or analog
signal to be fed to the machine tool axis
movement. This also checks whether machine tool
axis movement is at the same speed as directed by the
CPU. In case any safety conditionsrelated to the axis
are over ruled during movement or otherwise they are
reported to the CPU for corrective action.
Servo-ControlUnit
The decoded position and velocity control sign
als, generated by the CPU for the axis movement
forms the input to the servo-control unit. This unit in
turn generates suitable signals as command values. The

15. servo-drive unit converts the command values, which
are interfaced with the axis and the spindle motors
Fig.1
The servo-control unit receives the position
feedback signals for actual movement of the
machine tool axes from the feedback devices (like
linear scales, rotary encoders, resolves, etc.).The
velocity feedback is generally obtained through tacho
generators. The feedback signals are passed on to the
CPU for further processing. Thus the servo-
control unit performs the data communication
between the machine tool and the CPU.As explained
earlier, the actual movement of the slides on the
machine tool is achieved through servo drives.
The amount of movement and the rate of
movement are controlled by the CNC system
depending upon the type of feedback system used,
i.e. closed-loop or open-loop system (Fig.3)
Closed-loopSystem
The closed-loop system is characterized by the presence
of feedback. In this system, the CNC system send out
commands for movement and the result is continuously
monitored by the system through various feedback
devices. There are generally two types of feedback to a
CNC system -- position feedback and velocity
feedback.
OperationalPanel

16. Fig. Typical numerical control configuration of
Hinumerik 3100 CNC system

17. position Feedback
A closed-loop system, regardless of the type of
feedback device, will constantly try to achieve and
maintain a given position by self-correcting. As the
slide of the machine tool moves, its movement is fed
back to the CNC system for determining the position of
the slide to decide how much is yet to be traveled
and also to decide whether the movement is as per
the commanded rate. If the actual rate is not as per the
required rate, the system tries to correct it. In case this
isnot possible, the system declares fault and ini
tiates action for disabling the drives
and if necessary, switches off the machine.
Open-looppositioningcontrol Close-looppositioning
control
Comparison Circuit StopatZero Command
Counter Subtraction Circuit Position Control Tape
readerController Servo Motor Lead Screw Table
Amplifier Count ComparatorActive Buffer Storage Tape
readerServo Motor Lead Screw Table
Amplifier Position feedback signal ErrorSignal
Transducer

18. Fig. Open loop positioning system
Fig. Closed loop positioningsystem
Velocityfeedback
In case no time constraint is put on the system to
reach the final programmed position, then the
system may not produce the required path or
the surface finish accuracy. Hence, velocity
feedback must be present along with the position
feedback whenever CNC system are used for
contouring, in order to producecorrect interpolationand
also specified accelerationand deceleration velocities.
The tacho generator used for velocity feedback is
normally connectedto the motor and it rotates
whenever the motor rotates, thus giving an analog
outputproportional to the speed of motor. The
analog voltage is taken as speed feedback by the
servo-controller and swift action is taken by the

19. controller to maintain the speed of the motor
within the required limits.
Open-loopsystem
The open loop system lacks feedback. In this
system, the CNC system send out signals for
movement but does not check whether actual
movement is taking place or not. Stepper motors
are used for actual movement and the electronicsof
these stepper motors is run on
digital pulses from the CNC system. Since sy
stem controllers have no access to any real
timeinformation about the system performance, they
cannot counteract disturbancesappearingduring the
operation. They can be utilized in point to point
system, where loading torque on the axial motor is
low and almost constant.
Servo-drives
As shown in
Fig.1
The servo-drive receives signals from the CNC system
and transforms it into actual movement on the
machine. The actual rate of movement and
direction depend up on the command signal from
CNC system. There are various types of servo-drives,
viz., dc drives, ac drives and stepper motor drives. A
servo-drive consists of two parts, namely, the
motor and the electronicsfor driving the motor.

20. Keyboard
A keyboard is provided for the following purposes:
 Editing of part programs, tool data, and machine
parameters.
 Selection of different pages for viewing.
 Selection of operatingmodes, e.g. manual data
input.
 Selection of feed rate override and spindles speed
override.
 Execution of part programs.
 Execution of othertoll functions.
MachineControlPanel(MCP)
It is the direct interface between operator and the
NC system, enabling the operation of the machine
through the CNC system.
Fig.5
shows the MCP of Hinumerik 3100 system. During
program execution, the CNC controls the axis
motion, spindle function or tool function on a

21. machine tool, dependingupon the part program stored
in the memory. Prior to the starting of the machine
process, machine should first be prepared with some
specific tasks like,
•Establishinga correct reference point
•Loading the system memory with the required part
program
•Loading and checking of tool offsets, zero offsets, etc.
For these tasks, the system must be operated in specific
operatingmode so that these preparatoryfunctions can
be established.
Modesofoperation
Generally, the CNC system can be operatedin the
following modes:
•Manual mode
•Manual data input (MDI) mode
•Automatic mode
•Reference mode
•Input mode
•Outputmode, etc.
Control elements of the machine control panel
Manualmode
: In this mode, movement of a machine slide
can carried out manually by pressing the pa
rticular jog button (+ or -). The slide (axis) is
selected through an axis selector switch or through
individual switches (e.g., X+, X-, Y+, Y-, Z+,
Z-, etc.). The feed rate of the slide movement is

22. prefixed. CNC system allows the axis to be jogged at
high feed rate also. The axis movement can also be
achieved manually using a hand wheel interface instead
of jog buttons. In this mode slides can be moved in two
ways:
•Continuous
•Incremental
Continuousmode
: In This mode, the slide will move as long as the jog
buttonis pressed.
Incremental mode
: Hence the slide will move through a fixed
distance, which is selectable. Normally, system
allows jogging of axes in 1, 10, 100, 1000, 10000,
increments. Axis movement
Z -X -Z+X+
POWER ON
Emergency Stop
Cycle Mode select or Switch Spindlespeed override
Feed rate/rapid traverse override
Rapid traverse activate Direction keys Spindle
OFF ON
Feed Hold/StartCyclestart
NC ON
Key operated switch for input inhibit Block search
Single block Dry Run
Block Delete Rapid Traverse Override active Manual
encoderactive in X-and Z-axis resp.

23. Machine control panel of Hinumerik 3100
is at a prefixed feed rate. It is initiated by pressing the
proper jog+ or jog- key and will be limited to the no of
increments selected even if the jog button is
continuously pressed. For subsequent movement the
jog buttonhas to be released and once again pressed.
ManualDataInput(MDI)Mode
In this mode the following operationcan be performed:
•Buildinga new part program
•Editing or deleting of part program stored in the
system memory
•Enteringor editing or deleting of:------ Tool offsets
(TO)------ Zero offsets (ZO)------ Test data, etc.
Teach-in
Some system allows direct manual input of a
program block and execution of
the same.The blocks thus executed can be check
ed for correctness of dimensions and conseque
ntlytransferred into the program memory as part
program.
Playback
In setting up modes like jog or incremental, the
axis can be traversed either through the direction

24. keys or via the hand wheel, and the end position
can be transferred into the system
memory as command values. But the required feed
rates, switching functions and other auxiliary functions
have to be added to the part program in program editing
mode.Thus, teach-in and playback operating
method allows a program to created during the
first componentprove out.
AutomaticMode(AutoandSingleBlock)
In this mode the system allows the execution of a
part program continuously. The part program is
executed block by block. While one block is being
executed, the next block is read by the system,
analyzed and kept ready for execution. Execution
of the program can be one block after another
automatically or the system will execute a block,
stop the execution of the next block till it is initiated
to do so (by pressing the start button). Selection of part
program execution continuously(Auto) or one block at
a time ( Single Block ) is done through the machine
control panel. Many systems allow blocks (single or
multiple) to be retraced in the opposite direction.
Block retrace is allowed only when a cycle stop state is
established. Part program execution can resume and its
execution begins with the retraced block. This is
useful for tool inspection or in case of tool
breakage. Program start can be effected at any

25. block in the program, through theBLOCK SEARCH
facility.
ReferenceMode
Under this mode the machine can be referenced
to its home position so that all the
compensations (e.g., pitch error compensation)
can be properly applied. Part programs aregene
rally prepared in absolutemode with respect to machine
zero. Many CNC systems make it compulsory to
reference the slides of the machine to their home
positions before a program is executed while others
make it optional.
InputModeandOutputMode(I/OMode )
In this mode, the part programs, machine setup data,
tool offsets, etc. can be loaded/unloaded into/from the
memory of the system from external devices like
programming units, magnetic cassettes or floppy
discs, etc. During data input, some systems check
for simple errors (like parity, tape format, block
length, unknown
characters, program already present in
the memory,etc.). Transfer of data is done through a
RS232Cor RS422Cport.
OtherPeripherals
These include sensor interface, provision for
communication equipment, programming units, printer,
tape reader/puncherinterface, etc.
gives an overview of the system with few peripheral
devices.

26. ProgrammableLogicController(PLC)
A PLC matches the NC to the machine. PLCs were
basically introduced as replacement for hard wired relay
control panels. They were developed to be
reprogrammed without hardware changes when
requirements were altered and thus are reusable. PLCs
are now available with increased functions, more
memory and large input/outputcapabilities.
Fig.7
gives the generalized PLC block diagram. In the CPU,
all the decisions are made relative to controllinga
machine or a process. The CPU receives input data,
performs logical decisions based upon stored programs
and drives the outputs. Connectionsto a computer for
hierarchical controlare done via the CPU. The I/O
structureof the PLCs is one of their major strengths.
The inputs can be push buttons, limit switches, relay
contacts, analog sensor, selector switches, proximity
switches, float switches, etc. The outputscan be motor
starters, solenoid valves, position valves, relay coils,
indicatorlights, LED displays, etc. The field devices are
typically selected, supplied and installed by the machine
tool builderor the end user. The voltage level of the
field devices thus normally determines the type of I/O.
So, power to actuatethese devices must also be
supplied external to the PLC. The PLC power supply is
designated and rated only to operate the internal
portionsof the I/O structures, and not the field devices.
A wide variety of voltages, current capacities and types
of I/O modules are available.

27. INTERFACING
Interconnecting the individual elements of both the
machine and the CNC system using cables and
connectorsis called interfacing. Extreme care should
be taken during interfacing. Proper grounding in
electrical installation is most essential. This
reduces the effects of interference and guards
against electronic shock to personnel. It is also
essential to properlyprotect the electronic
equipment.Cable wires of sufficiently large cros
s-
sectional area must be used. Even though prope
r grounding reduces the effect of electrical interference,
signal cable requires additional protection. This is
generally achieved by using shielded cables. All
the cable shields must be grounded at controlonly,
leaving other end free. Other noise reduction techniques
includeusing suppression devices, proper cable
separation, ferrous metal wire ways, etc. Electrical
enclosures should be designed to provide proper
ambient conditionsfor the controller.
MONITORING
In addition to the care taken by the machine tool builder
during design and interfacing, basic control also
includes constantlyactive monitoring functions. This is
in order to identify faults in the NC, the interface
control and the machine at an large stage
to prevent damages occurring to the work piece, tool
or machine. If a fault occurs, first the machining

28. sequenceis interrupted, the drives are stopped, the
cause of the fault is stored and then displayed as an
alarm. At the same time, the PLC is informed that
an NC alarm exits. In Hinumerik CNC system, for
example, the following can be monitored:
•Read-in
•Format
•Measuring circuit cables
•Position encoders and drives
•Contour
•Spindlespeed
•Enablesignals
•Voltage
•Temperature
•Microprocessors
•Data transfer between operatorcontrolpanel and logic
unit
•Transfer between NC and PLC
•Change of status of buffer battery
•System program memory
•User program memory
•Serial interfaces
DIAGNOSTICS
The control will generally be provided with test
assistance for service purposes in order to display
some status on the CRT such as:
•

29. Interface signals between NC and PLC as well as
between PLC and machine
•Flags of the PLC
•Timers of the PLC
•Countersof the PLC
•Input/outputof the PLC For the output signals, it is
also possible to set and generate signal combinations for
test purpose sin order to observe how the machine react
to a changed signal. This simplifies troubleshooting
considerably.
MACHINEDATA
Generally, a CNC system is designed as a general-
purposecontrol unit, which has to be matched with the
particularmachine to which the system is interfaced.
The CNC is interfaced to the machine by means of data,
which is machine specific. The NC and PLC machine
data can be entered and changed by means of
external equipment or manually by the keyboard.
These data are fixed and entered during
commissioning of the machine and generally left
unaltered during machine operations. Machine data
entered is usually relevant to the axis travel limits,
feed rates, rapid traverse speeds and spindle
speeds, position control multiplication factor, Kv
factor, acceleration, drift compensation, adjustment
of reference point, backlash compensation, pitch error
compensation, etc. Also the optional features of the
control system are made available to the machine
tool builderby enablingsome of the bits of machine
data.

30. COMPENSATIONSFORMACHINEACCURACY
Machine accuracy is the accuracy of the movement of
the carriage, and is influenced by:(a) Geometric
accuracy in the alignment of the slide ways (b)
Deflection of the bed due to load (c)Temperature
gradients on the machine (d)Accuracy of the screw
thread of any drive screw and the amount of backlash
(lost motion)(e)Amount of twist (wind up) of
the shaft which will influence the measurement
of rotary transducersThe CNC systems offer
compensation for the various machines' accuracy.
These are detailed below
LeadScrew PitchErrorCompensation
To compensate for movements of the machine slide due
to in accuracy of the pitch along the length of the ball
screw, pitch error compensation is required. To begin
with, the pitch error curve for the entire length of the
screw is built up by physical measurement with the
aid of an external device (like laser). Then the required
compensation at predetermined pointsis fed in to the
system. Whenever a slide is moved, these
compensation are automatically added up by the
CNC system (
Fig.8
)
Fig.8

31. Typical error curve
BacklashCompensation
Whenever a slide is reversed, there is some lost motion
due to backlash between nut and the screw;
compensation is provided by the CNC system for the
motion lost due to reversal, i.e. extra movement is
added into the actual movement whenever reversal
takes place. This extra movement is equal to
backlash between the screw and the nut. This
has to be measured in advance and fed to the
system. This value keeps on varying due to wear of the
ball screws; hence the compensation value has to be
updatedregularly from time to time
Reference pointPositive end limit Pitch error (um)To
negative end limit
MM
Positive backlash the usual
caseT a b l e T a b l

32. e Ball screw Encoder Encoder Backlash Toothed
wheel Negative backlash Backlash here
Encoderactual value precedes the tablemovement
Actual movement of the table precedes the encoder
measurement
Fig.9
Backlash compensation
SagCompensation
Inaccuracy due to sag in the slide can be
compensated by the system. Compensations
required alongthe length of the slide have to be
physically measured and fed to the system. The system
automaticallyadds up the compensation to the
movement of the slide.
ToolNoseCompensation

33. Tool nose compensation normally used on tool for
turning centers. While machining chamfers, angles
or turning curves, it is necessary to make allowancefor
the tool tip radius; this radius is known as
Radius
compensation
. As shown in
Fig.10
(a), if the allowance is nit made, the edges of the tool
tip radius would be positioned at the programmed X
and Z coordinates, and the tool will follow the path
AB
and the taper produced will be incorrect. In order
to obtain correct taper, tool position has to be adjusted.
It is essential that the radius at the tip of the tool is
fed to the system to make an automatic adjustment
on the position and movement of the tool to get the
correct taper on the work. In

34. (b) The distance Xc is the adjustment necessary at
the start of the cut and distance Zc is the adjustment at
the end of the cut.
Tool nose radius compensation
CutterDiameterCompensation
The diameter of the used tool may be differ
ent from the actual value because of regrindi
ng of the tool or due to non-availability of the
assumed tool. It is possible to adjust the relative
position of cuttersize and this adjustment is known as
cutterdiameter compensation.
ToolOffset
A part program is generated keeping in mind a tool of a
particularlength, shape and thickness as a reference
tool. But during the actual mounting of toolson the
machine, different tools of varying lengths, thickness
and shapes may be available. A correction for
dimension of the tools and movements of the work
piece has to be incorporatedto give the exact machining
of the component.This is known as tool offset. This is
the difference in the positions of the centre line of the
tool holderfor different tools and the reference tool.
When a number of tools are used, it is necessary to
determine the tool offset of each tool and store it in the
memory of the controlunit.
Explains the function of the tool offset.
45Referencetool Tool no.1ZR=Settingdistance
for reference tool XR=Setting distance for reference

35. tool X offset for tool no.2Z offset for tool no.2Tool
no.2ZR ZR XR Z0X0
Normally, it is found that the size of the work piece
(diameter or length) is not within tolerance due to wear
of the tool; it is the possible to edit the value of offsets
to obtain the correct size. This is known as
Tool wear compensation.
PLCPROGRAMMING
The principle of operation of a PLC is determined
essentially by the PLC program memory, processor,
inputs and outputs. The program that determines PLC
operation is stored in the internal PLC program
memory. The PLC operates cyclically, i.e. when a
complete program has been scanned; it starts again
at the beginning of the program. At the beginning
of each cycle, the processor examines the signal
status at all inputs as well as the external timers and
countersand are stored in a process image input (PII).
During subsequent program scanning, the processor
the accesses this process
image.To execute the program, the processor
fetches one statement after another from the
programming memory and executes it. The results
are constantly stored in the process image output
(PIO) during the cycle. At the end of a
scanning cycle, i.e. program completion,

36. the processor transfers the contents of the process
image output to the output modules and to the
external timers and counters. The processor then begins
a new program
scan.STEP 5 programming language is used f
or writing user programs for SIMATIC S5 p
rogrammable controllers. The program can be
written and entered into the programmable
controller.
STRUCTUREDPROGRAMMING
The user program can be made more manageable and
straightforward if it is broken
downinto relative sections. Various software bl
ock types are available for constructing the use
program. Program blocks contain the user program
broken down into technologicallyor functionally
related sections (e.g. program block for transportation,
monitoring, etc.). Furtherblocks, such as program
blocks or function blocks can be called from a PB.
Organization blocks contain block calls
determining the sequence in which the PBs are
to be processed. It is therefore possible to call PBs
conditionally(dependingon certain conditions).In
addition, special OBs can be programmed by the user to
react to interruptionsduring
cyclic programming processing. Such an interrupt
can be triggered by a monitoring function if

37. one or several monitored events occur. Function
block is block with programs for recurrent and
usually complex function. In addition to the basic
operations, the user has a extended operationat his
disposal for developing function blocks. The
program in a function block is usually not written
with absolute operands (e.g. I 1.5) but with
symbolic operands. This enables a function block
to be used several times over with different absolute
operands. For even more complex functions, standard
function blocks are available from a program library.
Such FBs are available, e.g. for individual controls,
sequence controls, messages, arithmetic operations,
two step control loops, operatorcommunications,
listing, etc. These standard FBs for complex functions
can be linked it the user program just like user written
FBs simply by means of a call along with the relevant
parameters. The Sequenceblockcontain the step
enabling conditions, monitoring times and conditions
forthe current step in sequence cascade. Seque
nce blocks are employed, for example, to
organize the sequencecascade in communication with a
standard FB. The data blocks contain all fixed or
variable data of the user program.
CYCLICPROGRAMPROCESSING
The blocks of the user program are executed in
the sequence in which they specified in the
organization block.
INTERRUPTDRIVENPROGRAMPROCESSING

38. When certain input signal changes occur,
cyclic processing is interrupted at the next
block boundary and an OB assigned to this
event is started. The user can formulate his
response program to this interrupt in the OB. The
cyclic program execution is the resumed from the point
at which it was interrupted.
TIME CONTROLLEDPROGRAMEXECUTION
Certain Obs are executed at the predetermined time
intervals (e.g. every 100ms, 200ms, 500ms, 1s, 2s, and
5s). For this purpose, cyclic program execution is
interrupted at the block boundary and resumed
again at this point, once the relevant OB has
been executed. gives the organization and execution
of a structured user program.