Process Study of Machine Building Industry and Machine Control

Process Study of Machine Building Industry and Machine Control2014

Chapter 11. IntroductionConventionally relay circuits were used as the basic controllers in all machines. But as time passed, to meet the growing demand of the industries more number of relay circuits were required thus rendering a controlling circuit which was known for its complexity as well as its bulkiness. Thus the need for a compact and a high speed controller was met by the CNC- Computer Numeric Controller. CNC also serves as a reprogrammable, low maintenance required, low manpower required, highly reliable and an efficient machine.Industrial surveys in 1960's showed smaller machine components requiring several operations took long time to complete, Part sent to several machines before finished There was much "operator intervention" during machining processIn late 1960s and early 70s, begin to design machine that would perform several operations and do 90% of machining on one machine. There are three types: horizontal, vertical and universal type.Our project deals with twin horizontal machining Centre (HMC) which is a Traveling-column type where one or usually two tables where work is mounted (Column and cutter move toward work on one table while operator changes workpiece on other table).A horizontal machining center has a horizontal spindle. With a horizontal spindle, tools stick out from the side of the tool holder and cut across the side of a part (workpiece).HMC are far more expensive than equivalent capacity vertical machines, but have several advantages. Usually the tool holder of a horizontal machine is more rigid. Also when machining the side of a part, metal chips fall out of the area being cut, leaving an uncluttered cutting area. Whereas a vertical machining Centre has a vertical spindle, tools stick straight down from the tool holder and often cut across the top of a part. One disadvantage of this vertical machine is that when tools cut across the top of a part, the metal shavings called chips often pile up around the tool & interfere with the cutting action. The main function of this project deals with operations like Milling, Drilling (different sizes-5mm,8.5mm,10mm), Tapping, Back milling and as well as Boring (for smaller size). All these operations are made easier because of the possibility of Interpolation. It is designed specifically for the machining of the axles of the Ford vehicles.Our project is mainly a two way horizontal machining centre i.e., it consists of two sections-left hand side & right hand side with three axes (X,Y & Z) and a spindle on each of the side. It has a rotating indexing table where the workpiece is placed and the required job is done.While the machining is being carried out, the indexing table can rotate upto 180 (0-180) and then comes back to its original position. The HMC is a Semi-automatic machine, where few actions such as loading, unloading, reloading are done manually as per the customer scope.The machine consists of various mechanical components like hydraulics, pneumatics, lubrication unit, coolant system, base, fixtures, 3-axes slide assembly (servo), Hydraulic 180 oscillating table, component sensing unit, spindle with drive, automatic tool changer, machine guard (localized) and other electrical components.The operation that takes place in the indexing table is, initially the part that has to be machined is loaded and then the clamping of this part takes place due to the hydraulic mechanisms (solenoid valves gets electromechanically actuated). Once the clamping is done the indexing table is been rotated to 180 degree and positioned for the further machining process. Now the operator can access the other side of the rotating table facing him/her where another part can be loaded & clamped for the next machining. During the machining, required coolant system is made active which helps in dissipating the heat that is produced due to high speed machining operations. After the machining of the first part is completed, the table is rotated back to its original position and unclamping is done which is followed by unloading of the machined part, and then again reloading, clamping & so on takes place, whereas on the other side of the table second part is positioned and machining takes place. Thus operations that is being carried out are loading, clamping, rotating of the table, machining, again rotating back to its normal position, unclamping, unloading, reloading followed by clamping and thus the same cycle repeats.The coolant system of the machine involves coolant through spindle (CTS), base flush, bed wash pump, supply pump, hydraulics, radiators (fans) and also slat chip conveyor where this conveyor washes away these unnecessary metal chips remaining after machining. And lubrication motors used for lubricating the components like ballscrews, guideways which will help in machining of the part easily.The control system of the HMC is controlled using CNC i.e. SIEMENS SINUMERIK828D, with PLCs integrated in it. CNC has a wide range of applications mainly in automobile industries such as for milling and turning applications.Our project is a special purpose machine (SPM) thus it is concerned with an application of CNC which is to perform all sort of machining operations as per the customers specifications.

Fig 1.Twin Horizontal Machining Center.

Chapter 22. Literature Survey2.1 History of Machining CentersMilling is themachiningprocess of using rotarycuttersto remove materialfrom a workpiece advancing (orfeeding) in a direction at an angle with the axis of the tool. It covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes in industry and machine shops today for machining parts to precise sizes and shapes.Milling can be done with a wide range ofmachine tools. The original class of machine tools for milling was themilling machine(often called amill). After the advent ofcomputer numerical control (CNC), milling machines evolved intomachining centers(milling machines with automatic tool changers, tool magazines or carousels, CNC control, coolant systems, and enclosures), generally classified asvertical machining centers(VMCs) andhorizontal machining centers(HMCs). The integration of milling intoturning environments and of turning into milling environments, begun with live tooling for lathes and the occasional use of mills for turning operations, led to a new class of machine tools, multitasking machines(MTMs), which are purpose-built to provide for a default machining strategy of using any combination of milling and turning within the same work envelope.2.1.1 Brief Timeline of its Evolution1812- Eli Whitney credited for making the first true milling machine.1814- Rotary file byJacques de Vaucanson1818- milling machines developed by two federalarmoriesof the U.S. (SpringfieldandHarpers Ferry)1829- James Nasmythbuilt a milling machine very advanced for its time.It was tooled to mill the six sides of a hex nut that was mounted in a six-wayindexingfixture.1830- A milling machine built and used in the shop of Gay & Silver (aka Gay, Silver, & Co) was influential because it employed a better method of vertical positioning than earlier machines.1840s- milling machine development byFrederick W. Howe,Francis A. Pratt,Elisha K. Root, and others. The most successful milling machine design to emerge during this era was theLincoln miller, which rather than being a specific make and model of machine tool is truly a family of tools built by various companies (Robbins & Lawrence, theProvidence Tool Company, andBrown & Sharpe) on a common configuration over several decades.1860- Universal milling machine designed to tackle the 3-axis travel problem. First helical planning was designed by Frederick Howe & Joseph R. Brown.1870s-Brown & Sharpeand theCincinnati Milling Machine Companydominated the milling machine field with their variety of specialized production machines. Archetypal multipurpose milling centres included heavy knee-and-column horizontal-spindle design with power table feeds, indexing head, and a stout overarm to support the arbor.World war I- Around the end of World War I, machine tool control advanced in various ways that laid the groundwork for later CNC technology. In 1920 the new tracer design of J.C. Shaw was applied to Keller tracer milling machines for die-sinking via the three-dimensional copying of a template. This made die sinking faster and easier just as dies were in higher demand than ever before, and was very helpful for large steel dies such as those used to stamp sheets in automobile manufacturing. Such machines translated the tracer movements to input forservosthat worked the machine leadscrews or hydraulics. They also spurred the development ofantibacklash leadscrew nuts. All of the above concepts were new in the 1920s but became routine in the NC/CNC era. By the 1930s, incredibly large and advanced milling machines existed, such as the Cincinnati Hydro-Tel that presaged today's CNC mills in every respect except for CNC control itself.Bridgeport milling machine- major improvement to the milling machine.- often called a ram-type or turret-type mill because its head has sliding-ram and rotating-turret mounting.- The Bridgeport offered enduring advantages over previous models. It was small enough, light enough, and affordable enough to be a practical acquisition for even the smallest machine shop businesses, yet it was also smartly designed, versatile, well-built, and rigid. Its various directions of sliding and pivoting movement allowed the head to approach the work from any angle.1940s- By 1940, automation via cams, such as inscrew machines and automatic checkers- ideas involving servomechanisms were soon combined with the emerging technology of digitalcomputers.- 1950s, was powered by the military capital expenditures that pursued contemporary advancements in the directing of gun and rocket artillery and inmissile guidanceother applications in which humans wished to control thekinematics/dynamicsof large machines quickly, precisely, and automatically.1952- In 1952, numerical control reached the developmental stage of laboratory reality. The first NC machine tool was a Cincinnati Hydrotel milling machine retrofitted with a scratch-built NC control unit.

During the 1950s, numerical control moved slowlyfrom the laboratory into commercial service. For its first decade, it had rather limited impact outside of aerospace work. But during the 1960s and 1970s, NC evolved into CNC, data storage and input media evolved, computer processing power and memory capacity steadily increased, and NC and CNC machine tools gradually disseminated from an environment of huge corporations and mainly aerospace work to the level of medium-sized corporations and a wide variety of products. NC and CNC's drastic advancement of machine tool control deeply transformed the culture of manufacturing.1980s-present-Computers and CNC machine tools continue to develop rapidly. Thepersonal computerrevolution has a great impact on this development. By the late 1980s small machine shops had desktop computers and CNC machine tools. Soon after that hobbyists began obtaining CNC mills and lathes. Manufacturers have started producing economically priced CNCs machines small enough to sit on a desktop which can cut at high resolution materials softer than stainless steel. They can be used to make anything from jewelry to printed circuit boards to gun parts.2.2 How to choose this productThe CNC (computer numerical control) machining center is an automated machine tool capable of milling complex parts. The different types vary in complexity and are classed as either horizontal or vertical, depending on the orientation of the main spindle. These machines evolved from traditional machine tools. They differ in degree of automation, size and number axes.TechnologiesAs with milling machines, machining centers are categorized by the number of axes (three to five or more), which varies with the complexity of the parts to be manufactured. Configuration also varies: movable column, double column, gantry, etc. Spindle and axis drive systems also differ. The newest models use linear motors, faster, more compact and dynamic. Automatic pallet changing and robotization increase productivity.How to chooseChoice will depend primarily on product type, size and configuration, as well as required precision. Other important factors include productivity, the number of pieces in a production series and, ultimately, the machine's profitability.2.3 Leading Manufacturers in Machining Centers Bosch machining centers Breton machining centers DATRON machining centers DMG MORI machining centers GROB-WERKE machining centers Haas machining centers Mazak machining centers Toyota machining centers DMG MORI milling machines EMCO milling machines Haas milling machines

Chapter 33. Project Development

3.1 Concept DiagramThe Twin Horizontal Machining Center comprises of two identical sections to work upon both the sides of the axle simultaneously.Each section of the HMI comprises of Panel Processing Unit (vertical configuration) and Machine Control Panel which acts as an interface between the user and the machine. The interconnection between the HMI and the various blocks is represented in the concept diagram. An electronic hand wheel is also provided at the HMI in order to facilitate manual operation of the axis of machining center.This HMI is connected to the Power Module and the Control Supply Module which supervises the movements and functions performed by the 3 axis and the spindle. Each axis and the spindle is controlled by an AC servomotor whereas the spindle motor has added brakes with it.The Input/output module senses the inputs and provides output signals for the Control Circuit. Depending upon the function to be performed the CNC decides the parameters required and this information is communicated to the Power Module and Control Supply Module.The two sections are connected by a PN/PN Coupler by means of Profinet cables.3.2 Software Used: SINUMERIK 828D CNC E-PLAN ELECTRIC P8 ( 8.2 Version)

2nd Sys

Fig 3 Concept Diagram

Chapter 44. Hardware FundamentalsBased on the design details and the control required, switching, circuit interrupting the feedback devices required, are determined. The following are the electrical and electronic devices that have been incorporated in this design.4.1 Hydraulic PumpsNormally, the hydraulic pump draws in the hydraulic fluid from a supply reservoir (inlet or suction side) and propels it to the pump outlet (pressure side). From here the hydraulic fluid usually passes to the distribution assembly(directional control valve) from where it either flows back to the reservoir or is fed to the opposing resistance in the working assembly (e.g. the loaded piston of a hydraulic cylinder when a load is being raised) a pressure is built up in the hydraulic fluid. This pressure increases until it reaches a level sufficient to overcome the resistance. This means that the fluid pressure in the system is not generated by the pump from the outlet, but has to build up in the accordance with the resistances which oppose the fluid flow in the system. These resistances result from the external loading (useful load and mechanical friction) and the internal loading (fluid friction in the flow lines, screwed joints, fittings and valves). Fig 4.1 Hydraulic pumps4.2 Hydraulic CylindersThe hydraulic cylinder is the best known of the hydraulic components. It is the cylinder which plays a dominating role because it is usually the cylinder which serves as the starting point for the design of the whole hydraulic system. The Fig 4.2 Hydraulic Cylindershydraulic motor converts hydraulic power into mechanical power in the form of rotational movement. The cylinder on the other hand, converts the hydraulic power into linear movement. The task of generating linear movement (translation) movement is carried out by the cylinder with a minimum of structural outlay and with excellent power efficiency. Both force and velocity can be maintained constant throughout the whole of the piston stroke, or they can be varied at will. The versatility of the hydraulic cylinder is even further increased by the variety of fastenings and maintained which are possible, and by its combination with levers and linkages.

4.3 Pneumatic cylindersThey consist of a cylindrical body which is enclosed at both ends, containing a movable piston attached to a piston rod. The rod passes through an opening in one or both ends of the cylinder and is arranged so that air pressure, admitted into the cylinder, causes linear movement and pressure, and reciprocation of the piston. The air pressure which acts on the piston exerts a force which is transmitted by the piston rod to the work to be performed. They are versatile, fast-acting and provide a closely controlled force independent of piston position. The power requirement is relatively simple and with special seals they can withstand ambient temperature up to 45 Fahrenheit. Fig 4.3 Pneumatic Cylinder 4.4 Hydraulic motorHydraulic motor converts the hydraulic energy produced by the pump into mechanical energy (torque and rotating motion). It is normally of the same construction as hydraulic pumps. In many cases, pumps can operate directly as motors. The relational speed of the motor is dependent upon the rate of fluid flow through it. The torque that it delivers on the other hand is dependent upon the operating pressure. Fig 4.4 Hydraulic motor

4.5 Solenoid valveIt is one of the most common ways of operating a directional valve. A solenoid is an electrical device which consists basically of a plunger C frame and wire coil. The coil is wound inside the C frame. The plunger is free to move inside the coil. When an electric current passes through a coil of wire, a magnetic field is generated. This magnetic field attracts the plunger and pulls it into the coil. As the plunger moves in, it contacts a push pin and moves the directional valve spool to an extreme position. Fig 4.5 Solenoid valve 4.6 Circuit breakersA circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.4.6.1 Miniature Circuit Breakers [MCBs]The maximum priority is given to the operators safety. Second priority is given to the machine protection. Hence good earthing and safe electrical circuitry are given a lot of consideration. Fig 4.6.1 MCBs 1POLE 2POLE 3POLE Miniature circuit breakers rated between 2A to 10A both single phase and three phase have been used for different kinds of estimated maximum loads. The CBs rated 6A are connected in series with the induction motors and the 2A rated CBs are used for smaller loads like the machine lighting and cabinet lighting. CBs rated around 10A are used for power supply units that supply numerous small loads like the I/O cards, the controller, the display and the input devices. Applications1. It is used in both commercial and domestic buildings, bungalows and industrial premises in place and metal clad switches with rewirable fuses.1. It also provides safe and reliable protection for individual electric appliances, such as air conditioners, geysers, electrical cooking ranges, refrigerators etc.

4.6.2 MOCBsMotor circuit breakers are 3 pole thermal magnetic circuit breakers specially designed for control and protection of motors. All the induction motors chosen for continuous duty. During operation, due to excessive loading or current surges that occur due to disconnection of heavier load object switching on the respective motors pose a possibility of damage to the motor windings. Besides this, while working on heavier loads continuously, the conductors in the motor may overheat and get damaged. Hence a combination of MCB and an OVERLOAD CURRENT RELAY with adjustable time setting forms a protective device for the motor circuit. Both the relays and the MCB are housed in one module and this unit is called as a MOCB.

Fig 4.6.2 Motor circuit breaker 4.7 RELAYSA relay is an electrically operated switch used to turn on\off other circuits. It is a transducer, which changes an electrical signal to movement and then back to an electrical signal. It is useful if we want 1. A small current in one circuit to control another circuit containing a device such as a lamp or electric motor, which needs a large current.1. Several different switch contacts to be operated simultaneously.

The main principle used is either electromagnetic attraction or electromagnetic induction. A typical industrial relayFig 4.7.1 RelaysCurrent flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches. Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits the link is magnetic and mechanical.

Fig 4.7.2 Circuit Symbol for Relay

The relay's switch connections are usually labeled COM, NC and NO: 1. COM = Common, always connect to this, it is the moving part of the switch 1. NC = Normally Closed, COM is connected to this when the relay coil is off. 1. NO = Normally Open, COM is connected to this when the relay coil is on. ApplicationsThey are extremely used in the ultra-high-speed protection schemes of AC lines utilizing distance protection. Also, the main element of the differential relay in the equipment protection is also, in some cases, a static relay. Static relays are also used in over current earth fault protection schemes. Advantages of Relays1. Relays can switch AC and DC, transistors can only switch DC. 1. Relays can switch high voltages, transistors cannot. 1. Relays are a better choice for switching large currents (>5A). 1. Relays can switch many contacts at once. Disadvantages of Relays1. Relays are bulkier than transistors for switching small currents. 1. Relays cannot switch rapidly (except reed relays), transistors can switch many times per second. 1. Relays use more power due to the current flowing through their coil. 1. Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil. 4.8 CONTACTORS

Fig 4.8 ContactorContactors are electromagnetically operated switches that provide a safe and convenient means for connecting and interrupting branch circuits. It has no overload relays. Contactors are used in combination with pilot controlled devices to switch lighting and heating loads and to control AC motors in those cases where overload protection is provided separately. Pilot devices such as push buttons, float devices, pressure switches and thermostats are provided to operate contactors. A contactor increases safety and reduce wiring time. The technique includes:1. Shrouded terminals protect against accidental contact with live parts and thus increase safety.1. The screws being captive they do not fall down.1. Funnel shaped cable entrances reduce wiring time by facilitating quick location of the connecting wire.1. Cable end stops reduce wiring and testing time.1. Screw drivers guides reduce wiring time as they allow the use of power screw drivers.

4.9 SWITCHESA switch is a device, which can connect two points in a circuit or disconnect two points. If the switch is acting so as to connect two points it is said to be ON else it is said be OFF. The types of switches used are push button, knife, toggle, slider and micro switches to mention a few.4.9.1 Push Button Switches

Fig 4.9.1 push button switchNormal start and stop push buttons may be connected via controller I/O units, whereas emergency stop switches and push buttons to stop moving or potentially dangerous equipment are hard-wired. For ex: any push button which have to ensure that the machinery does not move whilst maintenance staff are working on it must function correctly whether the controller is operational or not- they must be hardwired, not fed into the PLC I/P channels or over communication links between two or more controllers. A common hardware approach to emergency stop requirements is to use a series of NC push buttons, which lock off (open) when pushed. These are single pole switches and can be in two positions: ON or OFF. In OFF, the knob projects out. When pressed the switch goes on and goes back off when released. These are used in circuits where a pause is required. 4.9.2 Limit SwitchesA limit switch is constructed much like the ordinary light switch used at home and office. It has the same ON/OFF characteristics. The limit switch usually has a pressure sensitive mechanical arm. When an object applies pressure on the mechanical arm, a switch circuit is organized. An object might have a magnet attached that causes a contact to rise and close when the object passes over the arm. Limit switches can be either NO or NC and may have multiple poles. A NO switch has continuity when pressure is applied and a contact is made, while a NC switch opens when pressure is applied and a contact is separated. This switch is used to activate a PLC device. Fig 4.9.2 Limit Switches

4.9.3 Pneumatic Pressure SwitchesThe pneumatic pressure switch combines a pressure sensing element and a spool valve to produce a switching device with an adjustable set point. The assembly is non electric using only air or inert gas in the switch unit, the assembly consists of two components, a switch unit and a transducer unit. The switch contains a mechanically actuated five ported spool valve, which provides the output signals. The transducer unit senses the pressure of a wide variety of liquids or gases and transmits a mechanical movement, at the preset pressure level to the switch unit.4.9.4 Reed switchThe switching elements operate in a gas filled capsule. High operating speeds are got owing to low inertia of moving parts. The upper and lower reeds are relatively stiff. Normally the reed relay is closed through the use of a permanent magnet. This action is neutralized and the relay opens on application of the solenoid field.

Fig 4.9.4 Top, middle: reed switches. Bottom: reed relay

4.10 SENSORSSensors are the transducers which gives an output signal when a physical quantity is measured.4.10.1 Proximity SensorsProximity sensors are the devices that indicate when one object is close to another. How close the object must be in order to activate the sensor is dependent on the particular device. Distance can be anywhere between several millimeters and several feet. It is an important component in an automatic control system. It transmits information relating to the operating condition of a machine to the logic processing system.1. Presence, passage flow of parts.1. End of travel.1. Rotation, counting etc.Basic working principleThe proximity method requires that the source and detector be installed on the same side of the object to be detected and aimed at a point in front of the sensor. When an object passes in front of the source and detector, light from the source is reflected from the objects surface back to the detector and the object is detected.4.10.2 Pressure SensorsPressure sensors are similar to limit switches except that the activating quantity in some form of fluid, either air, water or oil.ConstructionPressure switches utilizes seamless bellows as the sensing elements. They can be mounted with the help of the mounting screws provided with every switch. The mounting screws pass through the two mounting holes provided across the body of pressure switch.4.10.3 Photoelectric Sensors These may be categorized as either thermal detector or photon detectors. The thermal detectors involve a temperature sensitive element which is heated by the incident light. Essential parts of the device consist of some light-directing means which are more often lens-and-mirror systems to focus the radiant energy onto the receiver, which is generally a black body. Apart from these it consists of devices for adjusting the calibration which includes movable aperture and movable concave mirrors and the variable shunt resistor in the electrical circuit.The photon devices respond directly to the absorbed photons, either by emitting electron from a surface (the photoelectric effect) or by creating additional electron-hole pairs in the semiconductor.Features1. Withstands high pressure wash which simulates clearing procedure used in food and beverage processing.1. Ultra sonically welded lens, plus fully potted housing ensures watertight seal integrity.1. Rugged housing withstands strong acids, alkaline cutting fluids and thermal shock.1. Quick disconnect version decrease down time.

4.11 MOTORSThe 3- axes movement and the spindle movement is controlled by four A.C servomotors with the following ratings:A servomotor is a rotary actuator that allows for precise control of angular position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.

Servomotors are used in applications such as robotics, CNC machinery or automated manufacturing. X axis and Y axis motors- 16 N-m, 2.6 kW with encoder without brakes. Z axis motor- 20 N-m, 3.1 kW with encoder and brake. Spindle motor- 115 N-m, 12 kW with encoder

The other induction motors used in this Twin Horizontal Machining Center are : The Hydraulic Motor [Rated 11 A, 5.5 kW, 415 V] which is used to obtain the required hydraulic pressure needed to clamp and unclamp the work piece in place. The Radiator Motor [Rated 0.2 A, 45 W, 415 V] which is used for cooling purposes as radiator fans. The Cutting Coolant Motor [Rated 6 A, 3 kW, 415 V] which is used in cutting operations as well as coolant dispensing purposes (CTS-Coolant through spindle technology). The Base Flush Motor [Rated 8 A, 3.7 kW, 415 V] which is used during machining for coolant flushing purposes. The Slat Chip Conveyor Motor [Rated 1 A, 0.37 kW, 415 V] which is used to wash away the remaining waste metal chips. The Screw Conveyor Motor [Rated 0.75A, 0.18 kW, 415 V] which is used to circulate the coolant in the machining center as well as push the clogged metal chips away from the machining area and towards disposal. The Tool Magazine Motor [Rated 1.2 A, 0.37 kW, 415 V] which is used spin the tool magazine to provide access to different machining tool heads of various different sizes. The CAM Box Motor [Rated 2 A, 1.1 kW, 415 V] which is used to run the arm which places the required machining tool head from the automatic tool changer onto the spindle. The Lubrication Motor [Rated 0.6 A, 0.12 kW, 415 V] which is used for lubricating the components such as the ballscrews.

Fig 4a. Index Table

Fig 4b. Tool MagazineFig 4c. Solenoid valves

Fig 4d. The Control Panel

Fig 4e. Machining Spindle Fig 4f. Panel Processing Unit & Fig 4g. Coolant Motor.Machine Control Panel.

Chapter 55. Layout Diagrams

Chapter 66. Programmable Logic Controller6.1. IntroductionPLC (Programmable logic controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by analyzing its inputs and depending upon their state it turns on/off its outputs. The user enters required program, usually via software that gives the desired results.PLCs are used in many real world applications. For a machine building industry, the application of PLC plays a vital role. If it involves in machining, packaging, material handling, automated assembly etc. probably PLC is already used by them. With the usage of PLC we can save our time as well as cost. Almost any application that needs electrical control circuits will need a PLC. For example, assuming that when a switch turns on we need a solenoid to turn it on for 5 seconds and then turn it off regardless of how long the switch is on for. This can be done with a simple external timer. But what if the process involves 10 switches and solenoids? We would need 10 external timers. What if the process also needs to count how many times the switches individually turns on? Thus we need a lot of external counters.Hence need for PLC increases with the complexity of the process. The PLC can be programmed to count the inputs and turn the solenoid on at the specified time as well as many other counter actions.

6.2. PLC HistoryThe PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when production models changed. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as the relay systems needed to be rewired by skilled electricians.In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems.The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: MODICON, which stood for Modular Digital Controller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. The MODICON brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner.One of the very first 084 models built is now on display at MODICON's headquarters in North Andover, Massachusetts. It was presented to MODICON by GM, when the unit was retired after nearly twenty years of uninterrupted service. MODICON used the 84 moniker at the end of its product range until the 984 made its appearance.The automotive industry is still one of the largest users of PLCs.

Features Has specific features suited to industrial control: rugged, noise immune equipment Modular plug-in construction, allowing easy replacement/addition of units Standard input/output connections and signals levels Easily understood programming language Ease of programming and reprogramming in-plantThese features make programmable controllers highly desirable in a wide variety of industrial-plant and process-control situations. Programmable controllers have both hardware and software features that make them attractive as controllers of a wide range of industrial equipment.

PLC versus PCPLCPC

Environment The PLC was specifically designed for harsh conditions with electrical noise, magnetic fields, vibration, extreme temperatures or humidity.Common PCs are not designed for harsh environments. Industrial PCs are available but cost more.

Ease of Use By design PLCs are friendlier to technicians since they are in ladder logic and have easy connections. Operating systems like Windows are common. Connecting I/O to the PC is not always as easy.

Flexibility PLCs in rack form are easy to exchange and add parts. They are designed for modularity and expansion.Typical PCs are limited by the number of cards they can accommodate and are not easily expandable.

Speed PLCs execute a single program in sequential order. The have better ability to handle events in real time.PCs, by design, are meant to handle simultaneous tasks. They have difficulty handling real time events.

Reliability A PLC never crashes over long periods of time. ("Never" may not be the right word but its close enough to be true.) A PC locking up and crashing is frequent.

Programming languages Languages are typically fixed to ladder logic, function block or structured text.A PC is very flexible and powerful in what to use for programming.

Data management Memory is limited in its ability to store a lot of data. This is where the PC excels because of its hard drive. Any long term data storages, history and trendings are best done on a PC.

Table 1: Comparison between PLC and PC

6.3. Hardware designProgrammable controllers are purpose-built computers consisting of three functional areas: processing, memory and input/output. Input conditions to the PLC are sensed and then stored in memory, where the PLC performs the programmed logic instructions on these states. Output conditions are then generated to drive associated equipment. The action taken depends totally on the control program held in memory.

6.3.1. Programmable controller structure Programming Panel

ProgramMemory Control unit

Input circuits

Workmemory

Output Circuits

Power supply

Input Devices

Programmable controller

Output devices

Fig 6.3.1 Programmable controller structure

6.3.2. Central processing unit (CPU)The CPU is the brain of the system. Internally it contains various logic gate circuits. The CPU is a microprocessor based system that replaces control relays, counters, timers and sequencers. It is designed so that the user can enter the desired in relay ladder logic. The CPU accepts input data from various sensing devices, executes the stored user program from memory and sends appropriate output commands to the control devices. A direct current power source is required to produce the low level voltage used by processor and the I/O modules. This power supply can be housed in the CPU unit or may be separately mounted unit, depending on PLC system manufacturer. An internal communications highway, or bus system, carries information to and from the CPU, memory and I/O units, under control of the CPU. The CPU is supplied with a clock frequency by an external quartz crystal or RC oscillator.

6.3.3. Memory

For program storage all modern programmable controllers use semiconductor memory devices such as RAM read/write memory, or a programmable read-only memory of the EPROM or EEPROM families. After a program is fully developed and tested it may be loaded into a PROM or EPROM memory chip, which is normally cheaper than RAM devices. In addition to program storage, a programmable controller may require memory for other functions. Temporary buffer store for input/output channel status I/O RAM Temporary storage for status of internal functions, e.g. timers, counters, marker relays, etc.

6.3.4. Input/output units

The I/O units form the interface between the microelectronics of the programmable controller and the real world outside, and must therefore provide all necessary signal conditioning and isolation functions. This often allows a PLC to be directly connected to process actuators and transducers (e.g. pumps and valves) without the need for intermediate circuitry or relays. To provide this signal conversion programmable controllers are available with a choice of input/output units to suit different requirements. Every input/output point has a unique address or channel number which is used during program development to specify the monitoring of an input or the activating of a particular output within the program. Indication of the status of input/output channels is provided by light-emitting diodes (LEDs) on the PLC or I/O unit.The input output system forms an interface by which field devices are connected to the controller. The purpose of this interface is to condition the various signals received from or send to external field devices. The input devices such as push buttons, limit switches, sensors, selector switches are hard wired to the terminals on the input module. Output devices such as small motors, motor starters, solenoid valves and indicator lights are hard wired to the terminals on the output modules. These devices are also referred field or real world inputs and outputs. The terms field or real world are used to distinguish actual external devices that exists and must be physically wired from the internal user program that duplicates the function of relays, timers and counters.

6.3.5. Programming DeviceThe programming devices or terminal is used to enter the desired program into the memory of the processor this program is entered using relay ladder logic. The program determines the sequence of operation and ultimate control equipment or machinery. The programming device must be connected to controller only when entering or monitoring the program. The PLC can be easily programmed or reprogrammed with the help of these programming devices. PLC can be reprogrammed through an appropriate programming device: Programming Console PC Hand Programmer6.4. PLC OperationA PLC works by continually scanning a program. We can think of this scan cycle as consisting of 3 important steps. Typically there are more than three. Others are checking the system and updating the current internal counter and timer values.

Fig 6.4 PLC operationStep 1-CHECK INPUT STATUS-First the PLC takes a look at each input to determine if it is ON or OFF. In other words, is the sensor connected to the first input on? How about the second input? How about the third... It records this data into its memory to be used during the next step. Step 2-EXECUTE PROGRAM-Next the PLC executes the program one instruction at a time. If the program said that the first input was ON then it should turn on the first output. Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step. Step 3-UPDATE OUTPUT STATUS-Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were ON during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true. After the third step the PLC goes back to step one and repeats the steps continuously. One scan time is defined as the time it takes to execute the 3 steps listed above. 6.4.1. Modes of Operation:The programmable device can also be used to select the various processor modes of operation. The number of different operating modes and the method of accessing them vary with the manufacturer. Regardless of PLC model some common operating modes are:1. CLEAR MEMORY2. PROGRAM3. TEST4. RUNCLEAR MEMORY: Used to erase the contents of the on board RAM memory.PROGRAM: Used to enter the new program or update an existing one in the internal RAM memory.TEST: Used to operate or monitor the user program without energizing any outputs.RUN: Used to execute the user program. Input devices are monitored and output devices are energized accordingly.

6.5. Processor Memory OrganizationThe term processor memory organization refers to how certain areas of memory in a given PLC are used. Not all PLC manufacturers organize their memories in the same way. Although they do not all use the same memory makeup and terminology, the principles involved are same.

DATA TABLE

MAIN PROGRAMSUBROUTINESUBROUTINEUSER PROGRAMMESSAGE STORE AREA

Fig 6.5 Processor memory organizationThe above figure shows an illustration of memory organization known as memory map. Every PLC has a memory map. The memory space can be divided into two broad categories: the user program and the data table. The user program is where the programmed logic ladder diagram is entered and stored. It will account for most of the total memory of a given PLC system. It contains the logic that controls the machine operation. This logic consists of instructions requiring one word memory.The data table stores the information needed to carry out the user program .This includes such information as the status of the input and output devices timers and counter values, data storage and so on. Contents of the data table can be divided into two categories: status data and numbers or codes. Status is ON/OFF type of information represented by 1sand 0s stored in unique bit locations. Number or code information is represented by groups of bits, which are stored in unique byte or word locations. The data table can be divided into the following three sections according to the type of information to be remembered: input image table, output image table and timer and counter storage. The input image table stores the status of digital inputs, which are connected to input interface circuits.6.5.1. INPUT MODULE INPUT ON

001 00

INPUT IMAGE TABLE Fig 6.5.1 Input image tableThe above figure shows a typical switch as input to the input image table through the input modules. When the switch is closed, the processor detects the voltage at the input terminal and records that information by storing the binary 1 in the proper bit location. Each connected input has a bit in the input terminal to which the input is connected. The image table is constantly being changed to reflect the current status of the switch. If the input is on, its corresponding bit in the table is set to 1.If the input is off, the corresponding bit is reset to 0.The output image table is the array of 0 bits that controls the status of digital output devices, which are connected to the interface circuits.

6.5.2. OUTPUT MODULE

00100

OUTPUT MODULE OUTPUT ON Fig 6.5.2 Output image tableThe above figure shows a typical connection of an output image table through module. The status of this light [ON/OFF] is controlled by the user program and indicated by the presence 1s and 0s. Each connected output has a bit in the image table that corresponds to the terminal to which the output is connected. If the program calls for the specific output to be on , its corresponding bit in the table is set to 1. if the program calls for the output to be off, its corresponding bit in the table is set to 0.

6.6. Application of PLCs Automation of many different processes, such as controlling machines or factory assembling lines, is done through the use of PLCs. They have a wide area of applications in robotics. PLCs are mainly used for two specific tasks in robotics. Firstly, as a controller or reprogrammable part of robot and secondly as an overall system controller in a manufacturing cell containing one or more robots. Some of the other practical applications of PLCs are as follows: Asphalt distributor trucks are used in master-slave configuration to control the asphalt distribution actions. Preparing and packaging of preserved food is fully automated using PLC controlled machines. A gigantic coal mining machine has its electrical system completely controlled by a PLC. Automatic storage and retrieval system. Paint pigment dispensing machine. Testing equipments. Drilling machines, Tool and cutter grinder. Forming machines (here the machine is used for making different shapes on the metal).

6.7. Advantages of PLCs

FlexibilityIn the past, each different electronically controlled production machine required its own controller; 15 machines might require 15 different controllers. Now, it is possible to use one model of a PLC to run any one of the 15 machines. Furthermore, we would probably need fewer than 15 controllers, because one PLC can easily run many machines. Each of the 15 machines under PLC control would have its own distinct program.

Implementing changes and correcting errors With a wired relay type panel, any program alterations require time for rewiring of panels and devices. When a PLC program circuit or sequence design change is made, the PLC program can be changed from a keyboard sequence in minutes. Also if program errors have to be corrected in a PLC control ladder diagram, a change can be typed quickly.

Lower cost Advanced technology makes it possible to compact more functions into smaller and less expensive packages.

Pilot running A PC programmed circuit can be pre-run and evaluated in the office or lab. The program can be typed in, tested, observed and modified if needed, saving valuable factory time.

Speed of operation Relays can take an unacceptable amount of time to actuate. The operational speed of the PC logic operation is determined by scan time which is of milliseconds.

Ladder programming method The PLC programming can be accomplished in the ladder mode by an electrician or technician. Alternately, a PLC programmer who works in the digital or Boolean control system can also easily perform PLC programming.

Reliability Solid state devices are more reliable, in general, than mechanical or electrical relays and timers. The PLC is made up of solid state electronic components with very high reliabilities.

Security A program change cannot be made unless the PLC is properly unlocked and programmed. People on late shifts do not always record panel alterations made when the office area is locked up for the night.

6.8. Disadvantages of PLCs

Newer technology It is difficult to change some personnels thinking from ladders and relays to PLC computer concepts.

Fixed program applicationsSome applications are single function applications. It does not pay to use a PLC that includes multi programming capabilities if they are not needed. One example is in the use of drum controller/sequencers. Some equipment manufacturers still use a mechanical drum with pegs at an overall cost advantage.

Environmental considerations Certain process environments, such as high heat and vibrations, interface with the electronic devices in PLCs which limits their use.

Fail safe operation In relay systems, the stop buttons electrically disconnects the circuit if the power fails, the system stops. Furthermore, the relay system does not automatically restart when power is restored. This of course, can be programmed into the PLC. However in some PLC programs, we may have to apply an input voltage to cause a device to stop. These systems are not fail-safe. This disadvantage can be overcome by adding safety relays to a PLC system.

6.9. COMMUNICATIONSPLCs have built in communication ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus or DF1 is usually included as one of the communications protocols. Other options include various field buses such as DeviceNet or Profibus. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser.PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI (Human-Machine Interface) devices such as keypads or PC-type workstations. Some of today's PLCs can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100 Mbit/s.

Chapter 77. Basics of PLC programming7.1. ProgrammingPLC programs are typically written in a special application on a personal computer, and then downloaded by a direct-connection cable or over a network to the PLC. The program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory. Often, a single PLC can be programmed to replace thousands of relays.Recently, the International standard IEC 61131-3 has become popular. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations.Introduction to statement list: Statement list is a programming language using mnemonic abbreviations of Boolean logic operations. Boolean operations work on combination of variables that are true or false. A statement is an instruction or directive for the PLC.Statement List Operations: Load (LD) instruction. And (A) instruction. Or (O) instruction. Output (=) instruction.

7.2. Function Block Diagrams: Function block is represented as a box with the function name written in.Example

Fig 7.2 Function Block Diagrams LD: load O: or AN: and not (and a normally closed contact) ALD:AND the first LD with second LD

7.3. LADDER LOGICLadder logic is widely used to program PLCs, where sequential control of a process or manufacturing operation is required. Ladder logic is useful for simple but critical control systems, or for reworking old hardwired relay circuits. As programmable logic controllers became more sophisticated it has also been used in very complex automation systems.Ladder logic can be thought of as a rule-based language, rather than a procedural language. A "rung" in the ladder represents a rule. When implemented with relays and other electromechanical devices, the various rules "execute" simultaneously and immediately. When implemented in a programmable logic controller, the rules are typically executed sequentially by software, in a continuous loop (scan). By executing the loop fast enough, typically many times per second, the effect of simultaneous and immediate execution is relatively achieved to within the tolerance of the time required to execute every rung in the "loop" (the "scan time"). It is somewhat similar to other rule-based languages, like spreadsheets or SQL. However, proper use of programmable controllers requires understanding the limitations of the execution order of rungs. Ladder logic uses graphic symbols similar to relay schematic circuit diagrams.Ladder diagram consists of two vertical lines representing the power rails. Circuits are connected as horizontal lines between these two verticals.7.3.1 Ladder diagram features Power flows from left to right. Output on right side cannot be connected directly with left side. Contact cannot be placed on the right of output. Each rung contains one output at least. Each output can be used only once in the program. A particular input a/o output can appear in more than one rung of a ladder. The inputs a/o outputs are all identified by their addresses, the notation used depending on the PLC manufacturer.

Fig 7.3 ladder diagram representation

7.3.2. Basic Instructions ContactsNormally Open (NO) The Normally Open (NO) contact is closed (on) when the bit is equal to 1 Normally Closed (NC) The Normally Closed (NC) contact is closed (on) when the bit is equal to 0 Fig 7.3.2a ContactsThese instructions obtain the referenced value from memory or from the process image register if the data type is I or Q. In LAD, normally open and normally closed instructions are represented by contacts.One of the most confusing aspects of PLC programming for first time users is the relationship between the device that conducts a status bit and the programming function that uses a status bit. Two of the most common programming function are the normally open (NO) contact and the normally closed (NC) contact.Symbolically power flows through these contacts when they are closed. Normally open contact (NO) is true (closed) when the input or output status bit controlling the contact is 1. Normally closed contact (NC) is true (closed) when the input or output status bit controlling the contact is 0.Coil

Fig 7.3.2b Coil representationCoils represent relays that are energized when power flows to them. When a coil is energized, it causes a corresponding output to turn on by changing the status bit controlling that output to 1. The same output status bit may be used to control normally open and normally closed contacts elsewhere in the program.AND OperationEach network on a ladder represents a logic operation. The following programming example demonstrates an AND operation. Two contact closures and one output coils are placed on network 1. They are assigned addresses I0.0 (input 1) I0.1 (input 2) and (output 1). In this example I0.0 and I0.1 must be true for Q 0.0 to be true by looking at the functional block diagram representation.

I0.0 I0.1 Q0.0 Fig 7.3.2c AND representationOR operationIn this example an OR operation is used in. it can be seen that if either I0.3 (input 3) or input I0.4 (input 4) or both are true then output Q0.1 is true.

I0.3 Q0.1

I0.4Fig 7.3.2d OR representation

Set, Reset(N bits)

( S ) ( R ) Fig 7.3.2e Set, Reset The Set (S) and Reset (R) instructions set (turn on) or reset (turn off) the specified number of points (N), starting at the specified address (Bit). You can set or reset from 1 to 255 points. If the Reset instruction specifies either a timer bit (T) or counter bit (C), the instruction resets the timer or counter bit and clears the current value of the timer or counter.

Timers The On-Delay Timer (TON) instruction counts time when the enabling input is ON. When the current value (Txxx) is greater than or equal to the preset time (PT), the timer bit is ON. The On-Delay timer current value is cleared when the enabling input is OFF. This timer continues counting after the Preset is reached, and it stops counting at the maximum value of 32767. TON, TONR, and TOF timers are available in three resolutions. The resolution is determined by the timer number as shown in the chart below. Each count of the current value is a multiple of the time base. For example, a count of 50 on a 10-ms timer represents 500 ms. On-Delay timer-This type of timer simply "delays turning on". After the sensor (input) turns on it waits x-seconds before activating a solenoid valve (output). This is the most common timer. It is often called TON (timer on-delay), TIM (timer) or TMR (timer). Off-Delay timer- This type of timer is the opposite of the on-delay timer listed above. This timer simply "delays turning off". After the sensor (input) sees a target we turn on a solenoid (output). When the sensor no longer sees the target we hold the solenoid on for x-seconds before turning it off. It is called a TOF (timer off-delay) and is less common than the on-delay type listed above. Retentive or Accumulating timer- This type of timer needs 2 inputs. One input starts the timing event (i.e. the clock starts ticking) and the other resets it. The on/off delay timers above would be reset if the input sensor wasn't on/off for the complete timer duration. This timer however holds or retains the current elapsed time when the sensor turns off in mid-stream. For example, we want to know how long a sensor is on for during a 1 hour period. TON and TOF timers they will keep resetting when the sensor turns off/on. This timer however, will give the total or accumulated time. It is often called an RTO (retentive timer) or TMRA (accumulating timer).

7.4. Ladder Logic Programs7.4.1 Flowchart for Two-Hand Safety Mechanism

7.4.2 Flowchart of Clamping and Unclamping

7.4.3 Flowchart of Index Table

Chapter 88. Computer Numeric Controller8.1 IntroductionComputer Numerical Control (CNC) is a specialized and versatile form of soft automation and its applications cover many kinds, although initially it was developed to control the motion and operation of machine tools.Computer Numerical Control may be considered to be a means of operating a machine through the use of discrete numerical values fed into the machine, where the required input technical information is stored on a kind of input media such as floppy disc, hard disc, CD ROM, DVD, USB drive or RAM card etc. The machine follows a predetermined sequence of machining operations at the predetermined speeds necessary to produce a work piece of right shape and size and thus according to completely predictable results. A different product can be produced through re-programming and a low quality production run of different products is justified.The definition of a CNC given by Electronic Industry Association (EIA) is as follows:CNC is a system in which actions are controlled by the direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.In a simple word, a CNC system receives numerical data, interpret the data and then control the action accordingly.

8.2 Elements of CNC SystemA CNC system consists of following six major elements:1. Input device2. Machine control unit3. Machine Tools4. Driving System5. Feedback Devices

6. Display Unit

Fig. 8.2 Block Diagram Showing Different Elements of a CNC System

8.2.1 Input Devices8.2.1.1. Floppy Disk Drive Floppy disk is a small magnetic storage device for CNC data input. It has been the most common storage media up to the 1970s, in terms of data transfer speed, reliability, storage size, data handling and the ability to read and write. Furthermore, the data within a floppy could be easily edited at any point as long as you have the proper program to read it. However, this method has proven to be quite problematic in the long run as floppies have a tendency to degrade alarmingly fast and are sensitive to large magnetic fields and as well as the dust and scratches that usually existed on the shop floor. 8.2.1.2. USB Flash Drive A USB flash drive is a removable and rewritable portable hard drive with compact size and bigger storage size than a floppy disk. Data stored inside the flash drive are impervious to dust and scratches that enable flash drives to transfer data from place to place. In recent years, all computers support USB flash drives to read and write data that make it become more and more popular in CNC machine control unit.8.2.1.3 Serial Communication The data transfer between a computer and a CNC machine tool is often accomplished through a serial communication port. International standards for serial communications are established so that information can be exchanged in an orderly way. The most common interface between computers and CNC machine tools is referred to the EIA Standard RS-232. Most of the personal computers and CNC machine tools have built in RS232 port and a standard RS-232 cable is used to connect a CNC machine to a computer which enables the data transfer in reliable way. Part programs can be downloaded into the memory of a machine tool or uploaded to the computer for temporary storage by running a communication program on the computer and setting up the machine control to interact with the communication software.

1 2 3 4 5 6 7 8 8.2 18.2.3. 28.2.3. 38.2.3. 48.2.3. 58.2.3. 68.2.3. 78.2.3. 88.2.3. 1.2.2. 2.2.2. 3.2.2. 4.2.2. 5.2.2. 6.2.2. 7.2.2. 8.2.2. Machine Control Unit (MCU) The machine control unit is the heart of the CNC system. There are two sub-units in the machine control unit: the Data Processing Unit (DPU) and the Control Loop Unit (CLU). 8.2.2.1. Data Processing Unit On receiving a part program, the DPU firstly interprets and encodes the part program into internal machine codes. The interpolator of the DPU then calculate the intermediate positions of the motion in terms of BLU (basic length unit) which is the smallest unit length that can be handled by the controller. The calculated data are passed to CLU for further action. 8.2.2.2. Control Loop Unit The data from the DPU are converted into electrical signals in the CLU to control the driving system to perform the required motions. Other functions such as machine spindle ON/OFF, coolant ON/OFF, tool clamp ON/OFF are also controlled by this unit according to the internal machine codes.

1 1.2.3. 2.2.3. 3.2.3. 4.2.3. 5.2.3. 6.2.3. 7.2.3. 8.2.3. Machine Tool This can be any type of machine tool or equipment. In order to obtain high accuracy and repeatability, the design and make of the machine slide and the driving lead screw of a CNC machine is of vital importance. The slides are usually machined to high accuracy and coated with anti-friction material such as PTFE and Turcite in order to reduce the stick and slip phenomenon. Large diameter re circulating ball screws are employed to eliminate the backlash and lost motion. Other design features such as rigid and heavy machine structure; short machine table overhang, quick change tooling system, etc. Also contribute to the high accuracy and high repeatability of CNC machines. 1 2 3 4 5 6 7 8 8.2.4 1.2.3. 2.2.3. 3.2.3. 4.2.3. 8.2.4. 8.2.4. 8.2.4. 8.2.4. 8.2.4. 8.2.4. 8.2.4. 8.2.4. Driving System The driving system is an important component of a CNC machine as the accuracy and repeatability depend very much on the characteristics and performance of the driving system. The requirement is that the driving system has to response accurately according to the programmed instructions. This system usually uses electric motors although hydraulic motors are sometimes used for large machine tools. The motor is coupled either directly or through a gear box to the machine lead screw to moves the machine slide or the spindle. Three types of electrical motors are commonly used. 8.2.4.1. DC Servo Motor This is the most common type of feed motors used in CNC machines. The principle of operation is based on the rotation of an armature winding in a permanently energized magnetic field. The armature winding is connected to a commutator, which is a cylinder of insulated copper segments mounted on the shaft. DC current is passed to the commutator through carbon brushes, which are connected to the machine terminals. The change of the motor speed is by varying the armature voltage and the control of motor torque is achieved by controlling the motor's armature current. In order to achieve the necessary dynamic behaviour it is operated in a closed loop system equipped with sensors to obtain the velocity and position feedback signals. 8.2.4.2. AC Servo Motor In an AC servomotor, the rotor is a permanent magnet while the stator is equipped with 3-phase windings. The speed of the rotor is equal to the rotational frequency of the magnetic field of the stator, which is regulated by the frequency converter. AC motors are gradually replacing DC servomotors. The main reason is that there is no commutator or brushes in AC servomotor so that maintenance is virtually not required. Furthermore, AC servos have a smaller power-to-weight ratio and faster response.

8.2.4.3. Stepping Motor A stepping motor is a device that converts the electrical pulses into discrete mechanical rotational motions of the motor shaft. This is the simplest device that can be applied to CNC machines since it can convert digital data into actual mechanical displacement. It is not necessary to have any neither analog-to-digital converter nor feedback device for the control system. They are ideally suited to open loop systems. However, stepping motors are not commonly used in machine tools due to the following drawbacks: slow speed, low torque, low resolution and easy to slip in case of overload. Examples of stepping motor application are the magnetic head of floppy-disc drive and hard disc drive of computer, daisy-wheel type printer, X-Y tape control, and CNC EDM Wire-cut machine. 8.2.5 Feedback Device In order to have a CNC machine operating accurately, the positional values and speed of the axes need to be constantly updated. Two types of feedback devices are normally used positional feedback device and velocity feedback device. 8.2.5.1 Positional Feed Back Devices There are two types of positional feedback devices: linear transducer for direct positional measurement and rotary encoder for angular or indirect linear measurement. i. Linear Transducers A linear transducer is a device mounted on the machine table to measure the actual displacement of the slide in such a way that backlash of screws; motors, etc. would not cause any error in the feedback data. This device is considered to be of the highest accuracy and also more expensive in comparison with other measuring devices mounted on screws or motors. ii. Rotary Encoders A rotary encoder is a device mounted at the end of the motor shaft or screw to measure the angular displacement. This device cannot measure linear displacement directly so that error may occur due to the backlash of screw and motor etc. Generally, this error can be compensated for by the machine builder in the machine calibration process.8.2.5.2 Velocity Feedback Device The actual speed of the motor can be measured in terms of voltage generated from a tachometer mounted at the end of the motor shaft. DC tachometer is essentially a small generator that produces an output voltage proportional to the speed. The voltage generated is compared with the command voltage corresponding to the desired speed. The difference of the voltages can is then used to actuate the motor to eliminate the error8.2.6 Display Unit The Display Unit serves as an interactive device between the machine and the operator. When the machine is running, the Display Unit displays the present status such as the position of the machine slide, the spindle RPM, the feed rate, the part programmes, etc. In an advanced CNC machine, the Display Unit can show the graphics simulation of the tool path so that part programmes can be verified before the actually machining. Much other important information about the CNC system can also displayed for maintenance and installation work such as machine parameters, logic diagram of the programmer controller, error messages and diagnostic data.

8.3. SINUMERIK 828D

The SINUMERIK 828D is a complete unit comprising screen, CNC keyboard and CNC electronics. The motors can be easily connected to the digital drives via DRIVE-CLiQ. In combination with the modular structure of the SINAMICS S120 drive system, this design is conceived to ensure very simple and rugged installation with minimum wiring overhead. The performance range of the controller has been selected to meet the requirements of standardized turning and milling machines - from one-off production runs to industrial scale manufacture.With the SINUMERIK 828D we get a CNC system which is customized for the application in turning and milling machines. CNC, PLC, user interface and axis control for six CNC measuring circuits are all combined within a single compact unit. The controller provides comprehensive CNC functions such as kinematic transformations and a powerful tool management capability. The SINUMERIK 828D offers special capabilities for milling machines, with comprehensive drilling and milling operations, including milling with work piece planes swiveled to any degree and milling cylindrical work pieces. The performance of the controller and the new motion control allow you to achieve mirror finish surfaces for mold making applications, with a minimum machining time.The SINUMERIK 828D has eliminated all unnecessary functionalities; this is particularly noticeable in the graphical user interface. This means it is optimally suitable for use in the workshop. Operation, programming and maintenance can quickly be mastered without any heavy training requirement.

8.3.1 Machine spectrumThe SINUMERIK 828D is perfectly designed for equipping vertical and horizontal milling centers with up to six CNC measuring circuits. As well as the milling spindle and geometry axes (X, Y, and Z axis), other machine units can also be operated as an alternative.The SINUMERIK 828D includes CNC reversible clamping device (An axis) for milling and whole machining on cylindrical work pieces it also consists of swiveling heads or swiveling tables for milling and whole machining in swiveled machining planes.8.3.2. SINUMERIK 828D operator panels

The operator panel consists of a hard-wearing, die-cast magnesium alloy and is available in two versions, for horizontal and vertical mounting.The SINUMERIK 828D Comprises of the following for easier and smoother operation: 10.4 inches TFT color display Integrated QWERTY full CNC keyboard with short-stroke keys USB, CF card and Ethernet interfaces on the operator panel front

Fig.8.3.2. the Display Units for SINUMERIK 828D

8.3.3. Programming Format of SINUMERIK 828DWord address is the most common programming format used for CNC programming systems. This format contains a large number of different codes (Preparatory and Miscellaneous) that transfers program information from the part print to machine servos, relays, micro-switches etc., to manufacture a part. These codes, which conform to EIA (Electronic Industries Association) standards, are in logical sequence called a block of information. Each block should contain enough information to perform one machining operation.

Every program for any part to be machined must be put in a format that the machine control unit can understand. The format used on any CNC machine is built in by the machine tool builder and is based on the type of control unit on the machine. A variable-block format which uses words (letters) is most commonly used. Each instruction word consists of an address character, such as X, Y, Z, G, M, or S. Numerical data follows this address character to identify a specific function such as the distance, feed rate, or speed value.

8.3.4. CodesThe most common codes used when programming CNC machines tools are G codes (preparatory functions), and M codes (miscellaneous functions). Other codes such as F, S, D and T are used for machine functions such as feed, speed, cutter diameter offset, tool number, etc.

8.3.4a G-CodesG-codes are sometimes called as cycle codes because they refer to some action occurring on the X, Y and/or Z axis of a machine tool.The G-codes are grouped into categories such as Group 01, containing codes G00, G01, G02, G03, which cause some movement of the machine table or head. Group 03 includes either absolute or incremental programming, while Group 09 deals with canned cycles.For instance, a G00 code rapidly position the cutting tool while it is above the work piece from one point to another point on a job. During the rapid traverse movement, either the X or Y axis can be moved individually or both axes can be moved at the same time.

The table below lists out the functions of some most commonly used G-Codes, along with their group.

GROUPCODEFUNCTION

01G00Rapid Positioning

01G01Linear Interpolation

01G02Circular Interpolation Clockwise(CW)

01G03Circular Interpolation Counterclockwise (CCW)

06G20*Inch Input (inches)

06G21*Metric Input (mm)

00G28Return to Reference Point

00G29Return from Reference Point

07G40Cutter Compensation Cancel

07G41Cutter Compensation Left

07G42Cutter Compensation Right

08G43Tool Length Compensation Positive (+) Direction

08G44Tool Length Compensation Negative (-) Direction

08G49Tool Length Compensation Cancel

03G90Absolute Programming

03G91Incremental Programming

(*)- On some machines and controls, these may be G70 (inch) and G71 (metric).

Table 8.3.4a Most Common G-codes used in CNC Programming

8.3.4b M CodesM or Miscellaneous Codes are used to either turn ON or OFF the different functions which control certain machine tool operations.M-codes are not grouped into categories, although several codes may control same type of operations such as M03, M04 and M05 which control the machine tool spindle.

The table below lists out the functions of some most commonly used M-Codes.

Fig 8.3.4b commonly used M-codesCODEFUNCTION

M00Program Stop

M02End of program

M03Spindle Start(forward CW)

M04Spindle Start(reverse CCW)

M05Spindle Stop

M06Tool Change

M08Coolant ON

M09Coolant OFF

M10Chuck- Clamping(*)

M11Chuck- Unclamping(*)

M12Tailstock Spindle out(*)

M13Tailstock Spindle in(*)

M17Toolpost Rotation Normal(*)

M18Toolpost Rotation Reverse(*)

M30End of Tape and Rewind

M98Transfer to Subprogram

M99End of Subprogram

(*)- Refers only to CNC Lathes and Turning Centers

8.3.5 Block of InformationCNC information is generally programmed in blocks of five words, each word conforms to the EIA standards and they are written on a horizontal line. If five words are not included in each block, the Machine Control Unit (MCU) will not recognize the information; therefore the control unit will not be activated. 1 BLOCK OF INFORMATION CONSISTS OF 5 WORDS

NSequence No.N 0 0 1GCycle codesG 0 1XDimension

X 1 2 3 4 5YDimension

Y 0 6 7 8 9MMiscellaneous

M 0 3

1st Word 2nd Word 3rd Word 4th word5th WordFig.8.3.5 a Block of InformationUsing the example shown above, the five words are as follows:

N001: It represents the sequence number of the operation.

G01: It represents Linear Interpolation.

X12345: It will move the table1.2345 in. in a positive direction along X axis.

Y06789: It will move the table 0.6789 in. along the Y axis.

M03: It starts the spindle in forward clockwise direction.

8.4 Special Features of SINUMERIK 828D

The SINUMERIK 828D offers maintenance-free operation and high reliability, as the SINUMERIK 828D does not have a hard disk, battery or fan. Storage of part programs on a NVRAM (Non Volatile Random Access Memory), so no loss of data even during an extended loss of power. Highest machine availability thanks to reliable hardware. Maximum reliability due to compact design with few interfaces The same hardware is used for milling and for turning, leading to optimum spare parts utilization and management. Data handling is simpler due to the presence of easily accessible sockets for USB and compact flash card storage media on the front panel. Operator interface is provided in many languages so that the CNC is easy to learn and safe to operate. All the following languages are available on the control and can be changed online:1. Danish2. Finnish3. Japanese4. Dutch5. Polish6. Romanian7. Russian8. Swedish9. Slovakian10. Czech11. Turkish12. Hungarian

Chapter 99. Results and Conclusion

In this project we have programmed the PLC using Ladder Logic for accomplishing the following objectives: Incorporating Two-hand safety for the operation of the guard. Clamping and Unclamping of the workpiece onto the Indexing Table by means of Hydraulic Cylinders. The rotation of the Indexing table for simultaneous Loading and Machining of the workpiece.

This Twin Horizontal Machining Center was designed as per the client specifications i.e. Ford vehicles. It has been found that the degree of accuracy and precision of the machining is very high and meets the requirements of the customer satisfactorily.

The safety logic that we have designed for this machining center finds its applications in similar Special Purpose Machines.

REFERENCES[ 1 ]W. Bolton, Programmable Logic Controllers for PLC basics, Fifth Edition, Newnes, 2009 ISBN 978-1-85617-751-1, Chapter 1

[ 2 ] Gary Dunning and Thomson Delmar, Introduction to Programmable Logic Controllers for PLC basics, Learning Second Edition Second reprint 2003.

[ 3 ] M. A. Laughton, D. J. Warne (ed), Electrical Engineer's Reference book, for Programmable Controller, 16th edition, Newnes, 2003 Chapter 16

[ 4 ] Daniel Kandray, Programmable Automation Technologies, Industrial Press, 2010 ISBN 978-0-8311-3346-7, Chapter 8 for Introduction to Programmable Logic Controllers

[ 5 ] E. A. Parr, Industrial Control Handbook, Industrial Press Inc., 1999 ISBN 0-8311-3085-7 for Process study of Machine Building Industries.

[ 6 ] Smid, Peter, CNC Programming Handbook for CNC programming codes (3rd ed.) 2008, New York: Industrial Press, ISBN 9780831133474, LCCN 2007045901

[ 7 ] Siegel, Arnold. "Automatic Programming of Numerically Controlled Machine Tools", for Control Engineering, Volume 3 Issue 10 (October 1956), pp. 6570.

[ 8 ] Siemens, SINUMERIK 828D Manual- Control system overview for machine tools' sales people. Chapter 2, 5 11, 12 and 14.

[ 9 ]B.K Jha,CNC Programming Made Easy for CNC programming basics, Vikas Publishing House Pvt. Ltd 2003

[10] S.K Sinha, CNC Programming Using Fanuc Custom Macro B, illustrated, McGraw Hill Professional, 2010[11] E-Plan Electric P8 Classroom Training materials.[12] Robert. H Smith "Textbook of Advanced Machine Work" for Horizontal Milling process, reprint, third edition, revised , Chapter 10.

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Department of Electrical &Electronics Engineering, SET- Jain University69