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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

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:Handles much more complicated systems.Less and simple wiring.Increased Reliability. More Flexibility. Lower Cost .Faster Response. Easier to troubleshoot. Remote control capability. Communication Capability.

Disadvantages of PLCs:In contrast to microcontroller systems that have what is called an open architecture, most PLCs manufacturers offer only closed architectures for their products .PLC devices are proprietary, which means that parts and software from one manufacturer cant easily be used in combination with parts of another manufacturer, which limits the design and cost options.PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices.To maximize PLC performance and Flexibility, a number of Optional Modules must be added

Applications

Originally hardwired arrays of relays were used to control the operation of heavy machines that contain motors and other high power devices. PLCs were originally used to substitute the switching relay networks used in industrial applications, but now they can also be used to implement other tasks such as timing, delaying,counting, calculating, comparing and processing of analog signals. THANK YOU