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STUDY OF PLC IN CNC MACHINESB.CHAITANYA PRASADECE 4GROLL NO:08

CONTENTSAbout BHELCNC OverviewBlock Diagram of CNCBasic Parts of CNCTypes of CNC MachinesPLC OverviewWhy PLC?History of PLCPLC programmingAdvantages & DisadvantagesApplications

ABOUT BHELBHEL was established more than 50 years ago when its first plant was setup in Bhopal ushering in the indigenous Heavy Electrical Equipment Industry in India.

BHEL caters to core sectors of the Indian Economy viz., Power Generation's & Transmission, Industry, Transportation, Telecommunication, Renewable Energy, Defense, etc.

The Company today enjoys national and international presence featuring in the Fortune International -500 and is ranked among the top 10 companies in the world, manufacturing power generation equipment.

CNC OVERVIEWCNC stands for Computer Numerated Control.

CNC is the automotation of machine tools that are operated by precisely programmed commands encoded on a storage medium, as opposed to controlled manually via hand wheels or levers, or mechanically automated via cams alone.

CNC machines accept programs in the form of G Codes which are instructions that provide the direction and speed for the tool trajectory.

The major components associated with a CNC system are power supply, PLC, servo drives, CRT monitor and keyboard and some other special controllers.

CNC reads in the signal from the axis encoder from the measuring card which is placed in one of the slots of the controller.

Basic Parts Of CNC Machine: Central processing unit (CPU)

Servo-control unit

Operator control panel

Machine control panel

Programmable logic controllerTYPES OF CNC MACHINESTurning CentersMilling CentersVertical Machining CentersHorizontal Machining CentersDrilling MachinesEDM MachinesLaser-Cutting Machines

Important terms related to CNC machining Machine Zero - Machine zero is a point at the origin of the machines coordinate measuring system. All the Axis movements and other dimensions are measured from this point. It is similar to the origin of coordinate measuring system.

Machine reference point - It refers to the initial point of return for the purpose of measuring/feedback systems. Whenever a CNC machine is switched on the feedback system has to be initialized by referring this point on every axis.

Work Zero - This is the origin for the measuring of dimensions of workpiece. The programmer is free to select it anywhere on the drawing.

Absolute measuring system - In this measuring system all the dimensions are made from the work zero, which are defined. The machine control uses work zero as the reference point to position the tool during program execution. The main advantage of programming in absolute system is that any point can be readily changed without affecting subsequent dimensionsPLC OVERVIEWProgrammable Logic Controller(PLC) is a solid state device designed to perform logic functions.

PLC in general contains a processor and a human machine interface as monitor and signal interface between machine and PLC.

Essentially PLC is assembly of solid state digital electronic elements designed to make logical decisions and provide outputs.

History of PLCPLC was introduced in late 1960s First commercial & successful Programmable Logic Controllers was designed and developed by Modicon as a relay replacer for General Motors. Earlier, it was a machine with thousands of electronic parts.

Later ,in late 1970s,the microprocessor became reality & greatly enhanced the role of PLC permitting it to evolve form simply relay to the sophisticated system as it is today.

Why PLCRelay based Process or Machine Control is Expensive and Rigid.

Need for programmable and reconfigurable control

Move towards Flexible AutomationAreas of ApplicationProcess controlControl of MachineryControl of EquipmentsCertain Aspects of Control in CNC machines and Matching Centers

PLC Components Any PLC Has 1) A Microprocessor based CPU 2) Input/Output Section(I/O Section) Digital and analog I/O s 3) Programming Device Usually a Computer

PLC ProgrammingLadder diagram (LD) Sequential Function Charts (SFC) Function Block Diagram (FBD) Structured Text (ST) Instruction List (IL)

Advantages of PLCs:Reliability.Flexibility in programming and reprogramming.Cost effective for controlling complex systems.Small physical size, shorter project time.High speed of operation.Ability to communicate with computer systems in the plant.Ease of maintenance /troubleshooting. Reduced space. Energy saving.

Disadvantages of PLCs:PLC devices are proprietary it means that part or software of one manufacturer cant be used in combination with parts of another manufacturer.Limited design and cost optionFixed Circuit Operations.PLCs manufacturers offer only closed architectures.

Applications:Wherever automation is desired the PLCs are best suited to meet the task.

Few examples of industries where PLCs are used : 1) Robots manufacturing and control 2) Car park control 3) Train control station system 4) Food processing 5) Materials handling 6)Machine tools 7)Conveyer system etc.

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