Smart Home Scequrity System

CHAPTER-1 B.H.E.L AN OVERVIEW 1.1) OVERVIEW The “Maharatnas” declared by Indian Ministry of Heavy Industries are NTPC, VSNL, ONGC, IOCL, HPCL, SAIL, BHEL, IPCL, BPCL, etc. Therefore, B.H.E.L. is one of the Maharatnas and is the largest engineering enterprise of its kind in India with an excellent track record of performance. The company is engaged in engineering development and manufacturing of a wide variety of mechanical and electrical equipment for generation, Transmission and electricity. The company today enjoys National and International presence featuring in the “Fortunes Internationals 500” and is ranked among the top 12 companies in the world. B.H.E.L. has 14 manufacturing divisions, nine service centres and four power sectors regional centres and about 180 projects sites enables the company to its customers and provide them with suitable products, systems and service at competitive prices. Having attained “ISO 9000” certification, B.H.E.L.

is

now

embarking

1

upon

the total quality management.

1.2) BACKGROUND OF THE B.H.E.L Heavy Electrical (India) ltd. [HE (I) L] was set up in Bhopal in 1956 with a view to reach self-sufficiency in power equipment‟s vital for industrialization of the country, then B.H.E.L. came into existence in 1964. Three plants were stabilized under B.H.E.L. are as follows: High Pressure Boiler Point- Tiruchy (T.N.)(May 1965) Heavy Power Plant-Hyderabad(A.P)(Dec 1967) Heavy Electrical Equipment Plant –Haridwar (U.K.)( May 1967)

As there was need for development of power equipment manufacturing in India and also with a view to optimally utilize the resources HE (I) L. was merged in B.H.E.L.

2

1.3) PRESENT POSITION OF B.H.E.L. At present B.H.E.L. have 14 manufacturing units.

The major units are B.H.E.L. –

Bhopal, B.H.E.L. – Hyderabad, B.H.E.L. –Tiruchy, and B.H.E.L. – Hardwar. The

corporate

management

office

leadership,

is situated in New –Delhi and provides necessary top direction,

strategic-planning

and

operational

and

management support Services. It also coordinates the activities, function of various manufacturing, service divisions and numerous other functional and product groups. It also looks after the long – term planning in regards to resource and marketing and also planning for marshalling of human, physical and financial resources

3

CHAPTER-2 B.H.E.L. UNIT TABLE- 2.1) BHEL UNIT FACTORIES

PLACE

1. Heavy electrical equipment plant

BHOPAL

2. Control equipment division

BANGLORE

3. Heavy electrical equipment plant

HARIDWAR

4. Industrial valves plant

GOINDWAL

5. High tension ceramic

JAGDISHPUR

Insulation plan

6. Transformer plant

JHANSI

7. Heavy power equipment plant

HYDERABAD

8. High pressure boiler plant

TIRUCHIRAPALLI

4

2.2) COMPANY OBJECTIVES BUSINESS MISSION

To maintain a leading position as suppliers of quality equipment, system

and services in the field of conversion, transmission utilization and conversation of energy for application in the areas of electric power transportation, oil and gas exploitation industries utilize company‟s capabilities and resources to expand business into allied areas and other sectors of the economy like defiance, communication and electronics.

GROWTH : To ensure a steady growth by enhancing the competitive edge of B.H.E.L. in existingbusiness in new areas and international operators.

PEOPLE ORIENTATION: To enable each employee to achieve his potential, improve is potential, improve his capabilities perceive his role and responsibilities and success of the company. To invest in human resources continuously and be alive to their needs.

TECHNOLOGY : To

achieve

technological

excellence

in

operations

by

development

of

indigenous technology and efficient absorption and adoption of imported technologies to suit business needs and priorities and provide a competitive advantage to the company.

IMAGE : To fulfill the expectation which stakeholders like government as owner, employees, customers and the country at large house from B.H.E.L

5

TABLE 2.3-MANUFACTURING UNIT AND PROFILE UNIT

6

7

8

CHAPTER-3 TECHNICAL COLLABORATORS TABLE-3.1) COLLABRATORS

9

10

CHAPTER-4 B.H.E.L. (HARIDWAR): A PROFILE 4.1-PROFILEB.H.E.L. Haridwar, one of the keys manufacturing units of B.H.E.L. is located between Shivalik Mountains and Holy River GANGA. Its manufacturing plant includes two factories at Hardwar. On the northern side is heavy electrical equipment plant (H.E.E.P.), which commenced production in 1967 with know–how from M/S Kraft-work union, AG of Germany.

Now H.E.E.P. has a technical collaboration with M/S Siemens‟

Germany. For manufacturing of large size gas turbine. Located immediately to the south of H.E.E.P. is the central foundry forge plant (C.F.F.P.) which was primarily set up for manufacture of alloy steel casting and forging required for industry and power generation equipment. It was established in technical collaboration with M/S Crensot – Loire of France.

11

4.2) PROFILE OF HEEP ESTABLISHMENT AND DEVELOPMENT STAGES: 

DRP prepared



Initial product of electric motors started from Jan 1967.

in 1963 – 64 , construction started from Oct 1963.

 Major contribution /election /commissioning completed by 1971 –72 as per original DRP scope. 

Establishing in 1960‟s under the Indo- soviet agreement of 1959 and 1960 in

the area of scientific, technical and industrial co-operation.  Motor manufacturing technology up dated within siemen‟s collaboration during 1984 –87 . 

Facilities

being

modernized

continually

reconditing, retrofitting, technological, operational balancing

12

through Replacement,

4.3)HEEP PRODUCT PROFILE 1. THERMAL SETS: Steam turbines and generator up to 500MW capacity for utility and combined cycle applications; capability to manufacture up to 1000MW unit cycle.

2. GAS TURBINES: Gas turbines for industry and utility application; range-3 to 200 MW (ISO). Gas turbines based co-generation and combined cycle system.

3. HYDRO – SETS : Custom– built Pelton with

conventional

hydro

turbine

of kaplan,

Francis

and

matching generators upto 250 MW unit size.

Pump turbines with matching motor-generators Mini / micro hydro sets. Spherical butterfly and rotary valves and auxiliaries for hydro station .

4. EQUIPMENT FOR NUCLEAR POWER PLANTS: Turbines and generators upto 500MW unit size. Steam generator upto 500MW unit size. Reheaters / separators . Heat exchangers and pressure vessels.

5. CASTING AND FORGINGS: Sophisticated heavy casting and forging of creep resistant alloy steels, stainless steel and other grades of alloy meeting stringent international specifications.

6. DEFENCE PROCEDURE: Naval guns with collaboration of Italy.

13

CHAPTER-5 BRIEF DESCRIPTION OF MANUFACTURING BLOCKS 5.1) BLOCK-I Block-I, also known as Electrical Machines Block, is designed to manufacture Hydro generators, Turbo generators and Testing facilities for Turbo generators. There is also a special Test Bed for testing of turbo generators of capacity of 500 MW and above. Apart from facilities and equipment for manufacture of turbo generators, the Block also has a “Bebitting Section”.Bebitting of bearing liners for Turbo generators, Turbines, Hydro generators, is carried out in this section. The Block has its own over speed balancing installation; where the dynamic balancing of Turbo generator-rotors of less than 500 MW rating is done. Rotors having higher rating are balanced in OSBT of Block-III. Fabricated components are received from fabrication blocks (Block-II, IV, VI, VIII), while other castings, forgings are received from CFFP and other sources for Turbo generators, Hydro generators and Electrical motors. Stampings are received from Stampings manufacture section; Block-VI and coils, bars, insulating details and sheet metal components are received from Block-IV. These are then machined, assembled, tested and dispatched.

Figure 5.1.a)- Rotor winding 14

Figure5.1.b)Generator Testing

5.2)BLOCK-II Block-II, also known as Fabrication Block, is a feeder block for various productsSteam Turbines, Hydro Turbines, Turbo generators, Hydro generators, Electrical Machines, Apparatus and Control Gear, Aircraft and SRGM (Smooth Recoil Gun Mounting). The main processes in this Block are cutting, bending and welding of metal sheets etc. to form fabricated structures. The Block also has useful equipments like Hydraulic Bending Presses and Straightening Rollers. Other notable facilities include a CNC six-spindle drilling machine, a plasma-flame cutting machine, shot-blasting apparatus and various furnaces. The Block also has facilities for NDT (Non Destructive Testing) of various components. The following Non-Destructive tests can be conducted – DP Test (Die Penetration Test), MPI (Magnetic Particle Inspection), UT (Ultrasonic Testing)

and

Radiography

which

15

includes

X-ray

and

-ray

testing.

5.3) Block–III It Known as the TURBINE BLOCK, this is the major block for manufacturing turbines. All types of Hydro, Steam, Gas and Nuclear Turbines are manufactured and dispatched from this block. Blades of different stages are also manufactured here in this block.

5.4) Block- IV Block-IV, also called as CIM&ACM (Coil and Insulation Manufacturing & Apparatus and Control Gear Manufacturing), is a feeder block to Block-I. It is a feeder block for Class „F‟ windings for Turbo generators, Hydro generators and Class „F‟ and „H‟ insulation for AC and DC motors. It also supplies all insulation components for Turbo Control

generators, Hydro generators, and motors.

panels for Turbo generators, Hydro generators, Industrial drives for

motors, and Turbo generators auxiliaries, contactor relays and master controllers are also manufactured in this Block.

Figure 5.4.a-Block 4

16

5.5)Block -V Block-V, also called as Fabrication and Forge Block is again a feeder block. Fabrication work being done in this block is of Steam Turbine parts like Condenser, Water Box (Front and Rear), assemblies of LP cylinder, Storage Tanks etc.; Hydro Turbine parts, Hydro generator and motor assemblies and components. Forging of carbon, alloy and stainless steels are manufactured in this block. It is equipped with pneumatic hammers, gas-fired furnaces and hydraulic manipulators.

5.6)Block -VI Block-VI, also called as Fabrication Block, is also a feeder block. Manufacturing of all types of dies, including stamping dies and press forms is carried out in one bay, while stamping for Turbo generators, Hydro generators and motors are manufactured in other bay. The Block is equipped with Welding, Drilling, Shot Blasting and CNC Flame cutting facilities. The tems manufactured in this block are Condensers, Steam Turbine components (Oil Tanks and Hollow Guide Blades), Hydro Turbine components (Stay Rings), Hydro generator and motors (Stator Frames) etc.

5.7) Block -VII Block-VII, also called as Woodworking section, is also a feeder block. Bay-I, known as Packaging section manufactures packages for packaging and dispatch of various products.

5.8) Block- VIII Block-VIII, also called as Heat Exchanger Block, is designed to manufacture Heat Exchanger Units for Steam Turbines, Hydro Turbines, Turbo generators, Hydro generators etc. Blanks cut to size and shape are received from Block-II and Block-VI. These are assembled, welded and machined. The items manufactured here are – LP Heater, Ejectors, Gland Steam Coolers, Oil Coolers, Oil Tanks, Bearing Covers, Turbine shaft Covers, Oil Bath and Thrust Bearings 17

5.1) BLOCK-I Block-I, also known as Electrical Machines Block, is designed to manufacture Hydro generators, Turbo generators and Testing facilities for Turbo generators. There is also a special Test Bed for testing of turbo generators of capacity of 500 MW and above. Apart from facilities and equipment for manufacture of turbo generators, the Block also has a “Bebitting Section”. Bebitting of bearing liners for Turbo generators, Turbines, Hydro generators, is carried out in this section. The Block has its own over speed balancing installation; where the dynamic balancing of Turbo generator-rotors of less than 500 MW rating is done. Rotors having higher rating are balanced in OSBT of Block-III. Fabricated components are received from fabrication blocks (Block-II, IV, VI, VIII), while other castings, forgings are receivedfrom CFFP and other sources

for

Turbo

generators,

Hydro

generators

and Electrical motors.

Stampings are received from Stampings manufacture section; Block-VI and coils, bars, insulating details and sheet metal components are received from BlockIV.

These

are

then

machined, assembled, tested and dispatched.

18

CHAPTER-6 INTRODUCTION Development of computerized numerical controlled (CNC) machines is an outstanding contribution to the manufacturing industries. It has made possible the automation of the machining process with flexibility to handle small to medium batch of quantities 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 components combining operations like milling, drilling, boring and taping. Further, the concept of multi-operations was also extended for machining cylindrical components, which led to the development of turning centers.

6.1) ADVANTAGES OF CNC MACHINES 

Higher flexibility



Increased productivity



Consistent quality



Reduced scrap rate



Reliable operation



Reduced non productive time



Reduced manpower



Shorter cycle time



High accuracy



Reduced lead time



Just in time (JIT) manufacture



Automatic material handling



Lesser floor space



Increased operation safety



Machining of advanced material.

19

CHAPTER-7 CNC SYSTEMS INTRODUCTION Numerical control (NC) is a method employed for controlling the motions of a machine tool slide and its auxiliary functions with input in the form of numerical data. A computer numerical control (CNC) is a microprocessorbased 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, depending on 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 constructed with a NC unit integrated with a programmable logic controller (PLC) and some times with an additional external PLC (non-integrated). The NC controls the spindle movement and the speeds and feeds in machining. It calculates the traversing path of the axes as defined by the inputs. The PLC controls the peripheral actuating elements of the machine such as solenoids, relay coils, etc. Working together, the NC and PLC enable the machine tool to operate automatically. Positioning and part accuracy depend on the CNC system's computer control algorithms, the system resolution and 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 result in poorer part accuracy. This chapter gives an overview of the configuration of the CNC system, interfacing and introduction to

20

7.1)CONFIGURATION OF THE CNC SYSTEM Fig.7.1.a shows a schematic diagram of the working principle of a NC axis of a CNC machine and the interface of a CNC control.

Fig.7.1.a Schematic diagram of a CNC machine tool A CNC system basically consists of the following: 

Central processing unit (CPU)



Servo-control unit



Operator control panel



Machine control panel



Other peripheral device



Programmable logic controller (PLC)

Fig.7.1.b gives the typical numerical control configuration of Hinumerik 3100 CNC system

21

CENTRAL PROCESSING UNIT 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 decoded and 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 out, backlash, etc.) are calculated by the CPU depending upon the corresponding inputs made available 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 continuous necessary 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.

Speed Control Unit This unit acts in unison with the CPU for the movement of the machine axes. The CPU sends the control signals 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 conditions related to the axis are overruled during movement or otherwise they are reported to the CPU for corrective action.

Servo-Control Unit The decoded position and velocity control signals, 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 servo- drive unit converts the command values, which are interfaced with the axis and the spindle motors (Fig.7.1.a). 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

22

processing. Thus the servo-control unit performs the data communication between the machine tool and the CPU. As explained earlier, the actual movements 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 (Fig7.1.b)

Closed-loop System 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.

Fig.7.1(b)Typical numerical control configuration of Hinumerik 3100 CNC system

23

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 is not possible, the system declares fault and initiates action for disabling the drives and if necessary, switches off the machine.

Open-loop positioning control

Close-loop positioning control

Fig.7.1.c Open-and Closed-loop positioning system.

24

Velocity feedback 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 produce correct interpolation and also specified acceleration and deceleration velocities. The tacho generator used for velocity feedback is normally connected to the motor and it rotates whenever the motor rotates, thus giving an analog output proportional to the speed of motor. The analog voltage is taken as speed feedback by the servocontroller and swift action is taken by the controller to maintain the speed of the motor within the required limits.

Open-loop system 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 electronics of these stepper motors is run on digital pulses from the CNC system. Since system controllers have no access to any real time information about the system performance, they cannot counteract disturbances appearing during 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.7.1.a 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 upon 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 electronics for drivingamotor.

25

Operator Control Panel Fig.7.1.b shows a typical Hinumerik 3100 CNC system's operator control panel. The operator control panel provides the user interface to facilitate a twoway communication between the user, CNC system and the machine tool. This consists of two parts:  Video Display Unit (VDU)  Keyboard

Video Display Unit (VDU) The VDU displays the status of the various parameters of the CNC system and the machine tool. It displays all current information such as: 

Complete information of the block currently being executed



Actual position value, set or actual difference, current feed rate, spindle speed



Active G functions



Main program number, subroutine number



Display of all entered data, user programs, user data, machine data, etc.



Alarm messages in plain text



Soft key designations

In addition to a CRT, a few LEDs are generally provided to indicate important operating modes and status. Video display units may be of two types: 1. Monochrome or black and white displays 2. Color displays

26

Operator's and machine panel

Fig.7.1.d Operator control panel of Hinumerik 3100 system

27

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 operating modes, e.g. manual data input.



Selection of feed rate override and spindles speed override.



Execution of part programs.



Execution of other toll functions.

Machine Control Panel (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 machine tool, depending upon 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, Establishing a 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 operating mode so that these preparatory functions can be established.

28

Control elements of the machine control panel

Fig.7.1.(e) Machine control panel of hinumerik 3100

29

CHAPTER-8 Modes of operation 8.1) MODE OF OPERATION Generally, the CNC system can be operated in the following modes: 

Manual mode



Manual data input (MDI) mode



Automatic mode



Reference mode



Input mode



Output mode, etc

Manual mode: In this mode, movement of a machine slide can carried out manually by pressing the particular 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 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

Continuous mode: In This mode, the slide will move as long as the jog button is 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 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 button has to be released and once again pressed.

30

Manual Data Input (MDI) Mode In this mode the following operation can be performed: 

Building a new part program



Editing or deleting of part program stored in the system memory

Entering or editing or deleting of: ------ Tool offsets (TO) ------ Zero offsets (ZO)

------ Test data, et

Teach-in Some system allows direct manual input of a program block and execution of the same. The blocks thus executed can be checked for correctness of dimensions and consequently transferred 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 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 component prove out.

31

Automatic Mode (Auto and Single Block) 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 block in the program, through the BLOCK SEARCH facility.

Reference Mode 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 are generally prepared in absolute mode 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.

32

Input Mode and Output Mode (I/O Mode) 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 RS232C or RS422C port.

Other Peripherals These include sensor interface,

provision for communication equipment,

programming units, printer, tape reader/puncher interface, etc. Fig.8.1.a gives an overview of the system with few peripheral devices.

Programmable Logic Controller (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/output capabilities. Fig.7 gives the generalized PLC block diagram. In the CPU, all the decisions are made relative to controlling a machine or a process. The CPU receives input data, performs logical decisions based upon stored programs and drives the outputs. Connections to a computer for hierarchical control are done via the CPU. The I/O structure of 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 outputs can be motor starters, solenoid valves, position valves, relay coils, indicator lights, LED displays, etc. The field devices are typically selected, supplied and installed by the machine tool builder or the end user. The voltage level of the field devices thus normally determines

the

type

of

I/O. 32

So,

power

to

actuate

these

devices must also be supplied external to the PLC. The PLC power supply is designated and rated only to operate the internal portions of the I/O structures, and not the field devices. A wide variety of voltages, current capacities and types of I/O modules are available.

33

INTERFACING Interconnecting the individual elements of both the machine and the CNC system using cables and connectors is 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 properly protect the electronic equipment. Cable wires of sufficiently large cross-sectional area must be used. Even though proper 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 control only, leaving other end free. Other noise reduction techniques include using suppression devices, proper cable separation, ferrous metal wire ways, etc. Electrical enclosures should be designed to provide proper ambient conditions for the controller.

MONITORING In addition to the care taken by the machine tool builder during design and interfacing, basic control also includes constantly active 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 sequence is 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



Spindle speed



Enable signals



Voltage 34



Temperature



Microprocessors



Data transfer between operator control panel 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: Interface signals between NC and PLC as well as between PLC and machine Flags of the PLC Timers of the PLC Counters of the PLC Input/output of the PLC For the output signals, it is also possible to set and generate signal combinations for test purposes in order to observe how the machine react to a changed signal. This simplifies trouble shooting considerably.

MACHINE DATA Generally, a CNC system is designed as a general-purpose control unit, which has to be matched with the particular machine 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

35

m are made available to the machine tool builder by enabling some of the bits of machine data.

COMPENSATIONS FOR MACHINE ACCURACY 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 transducers

36

CHAPTER-9 PLC PROGRAMMING 9.1) PLC PROGRAMING 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 counters and 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, 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 for writing user programs for SIMATIC S5 programmable controllers. The program can be written and entered into the programmable controller as in:

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

Statement list (STL)



Control system flowchart (CSF)



Ladder diagram (LAD)

The statement list describes the automation task by means of mnemonic function designations. The control system flowchart is a graphic representation of the automation task. The ladder diagram uses relay ladder logic symbols represent the automation task. The statement is the smallest STEP 5 program component. It consists of the following: Operation, i.e. what is to be done? A = AND operation (series connection) O= OR operation (parallel connection) S= SET operation (actuation) E.g. :

Operand, i.e. what is to be done with? E.g. I 4.5, i.e. with the signal of input 4.5 The operand consists of: Operand identifier (I = input, Q = output, F = flag, etc.) Parameter, i.e. the number of operand identifiers addressed by the statement.

For inputs, outputs and flags (internal relay equivalents), the parameter consists of the byte and bit addresses, and for timers and counter, byte address only.

The statement may include absolute operands, e.g. I 5.1, or symbolic operand, e.g. I LS1. Programming is considerably simplified in the later case as the actual plant designation is directly used to describe the device connected to the input or output. Typically, a statement takes up one word (two bytes) in the program memory.

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9.2-STRUCTURED PROGRAMMING The user program can be made more manageable and straightforward if it is broken down into relative sections. Various software block types are available for constructing the user program.

Program blocks (PB) contain the user program broken down into technologically or functionally related sections (e.g. program block for transportation, monitoring, etc.). Further blocks, such as program blocks or function blocks can be called from a PB.

Organization blocks (OB) contain block calls determining the sequence in which

the

PBs

are

to

be processed. It is therefore possible to call PBs

conditionally (depending on certain conditions). In addition, special OBs can be programmed by the user to react to interruptions during cyclic programming processing. Such an interrupt can be triggered by a monitoring function if one or several monitored events occur.

Function block (FB) is block with programs for recurrent and usually complex function. In addition to the basic operations, the user has a extended operation at 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, operator communications, 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 Sequence block (SB) contain the step enabling conditions, monitoring times and conditions for the current step in sequence cascade. Sequence blocks

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are employed, for example, to organize the sequence cascade in communication with a standard FB.

The data blocks (DB) contain all fixed or variable data of the user program

9.3-CYCLIC PROGRAM PROCESSING The blocks of the user program are executed in the sequence in which they specified in the organisation block.

9.4-INTERRUPT DRIVEN PROGRAM PROCESSING 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.

9.5-TIME CONTROLLED PROGRAM EXECUTION 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. Fig.9.5.a gives the organisation and execution of a structured user program.

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9.6-EXAMPLES OF PLC PROGRAM Before attempting to write a PLC program, first go through the instruction set of the particular language used for the equipment, and understand the meaning of each instruction. Then study how to use these instructions in the program (through illustration examples given in the manual). Once the familiarization task is over, then start writing the program. Follow the following steps to write a PLC program.

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List down each individual element (field device) on the machine as Input/Output. Indicate against each element the respective address as identifier during electrical interfacing of these elements with the PLC.

Break down the complete machine auxiliary functions that are controlled by the

PLC into individual, self contained functions.

Identify each individual function as separate block (PBxx/FBxx) Once the PBs and FBs for each function are identified, take them one by one for writing the program. List down the preconditions required for the particular function separately. Note down the address of the listed elements. Write down the flow chart for the function. Translate the flow chart into PLC program using the instructions already familiarized. Complete the program translation of all individual functions in similar lines. Check the individual blocks independently and correct the program to get the required results. Organize all the program blocks in the organization block depending upon the sequence in which they are supposed to be executed as per the main machine function flow chart. Check the complete program with all the blocks incorporated in the final program.

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CHAPTER-10 CONCLUSION

The industrial training at BHEL Haridwar helped us in improving our practical

knowledge and awareness regarding CNC machines to a large extent.

Here we came to know about the technology and material used in manufacturing of CNC machines. Besides this, we also visualized the parts involved or equipments used in the power generation.

Here we learnt about how the electrical equipments are being manufactured and how they tackle the various problems under different circumstances. At least we could say that the training at BHEL Haridwar is great experience for us and it really helped us in making or developing our knowledge about CNC machines and other equipment

used

in

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power

generation.

REFERENCES

Books A text book of electrical machines by P.S.BIMBRA A text book of electrical technology by B.L.THERAJA

Other BHEL Internal material

Sites http://www.bhel.com http://en.wikipedia.org/wiki/Turbo_generator http://en.wikipedia.org/wiki/Hydrogen-cooled_turbogenerator

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