 Friends, I am Naval Emul working as the assistant professor in mechanical engineering department at Vulture Institute of Technology, Sholapur. In this video, we are going to see the fundamentals of CNC machines part 2. Learning outcome at the end of this session, students will be able to understand fundamentals of CNC machines and applications of the CNC. To understand the working principle of the CNC machines, to understand the characteristics of the driving systems, to understand the characteristics of the feedback devices, to understand the applications of the CNC machines. Contents of this video are elements of the CNC system, applications of the CNC and references. So, we will have a quick revision of the elements of the CNC system. First is input devices, second machine control unit, machine tool, driving system, feedback devices, display unit. Input devices are explained in detail in video number 1. Now we are going to see from the second major element that is machine control unit. Machine control unit is also called as MCU. The machine control unit is the heart of the CNC system. There are two subunits in the machine control unit, the data processing unit that is also called as DPU and the control loop unit CLU. Data processing unit on receiving a part program, the data processing unit firstly interprets and encodes the part program into internal machine codes. The interpolator of the DPU then calculate the intermediate position of the motion in terms of basic length unit that is BLU which is the smallest unit length that can be handled by the controller. The calculated data are passed to CLU for further action. Second control loop unit, the data from the DPU are converted into electrical signals in the control loop unit to control the driving system to perform the required motions. The other functions such as machine spindle on or off, coolant on or off, tool clamp on or off are also controlled by this unit according to the internal machine codes. Third we are going to look at machine tool. This can be any type of machine tool or equipment. In order to obtain high accuracy and repeatability, the design and making of the machine slide and the driving lead screw of a CNC machine is a vital importance. The slides are usually machined to a high accuracy and coated with anti-friction material such as PTFE and truncate in order to reduce the stick and slip phenomenon. Large diameter recirculating ball screws are employed to eliminate the backlash and lost motion. Other design features such as rigid and heavy machine structures, short machining table, overhang, quick change, tooling system etc are also contributed to the high accuracy and repeatability of the CNC machines. So figure one shows the ball screw in the CNC machine and figure two shows the ball screw structure which is placed inside the CNC machine. Fourth we look at driving system. The driving system is an important component of the CNC machine as the accuracy and repeatability depend very much on the characteristics and performance of the driving system. First we will see what is DC server 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. Second AC server motor. In an AC server motor the rotor is a permanent magnet while the stator is equipped with a three phase winding. The speed of the rotor is rotational frequency of the magnetic field of the stator which is regulated by the frequency converter. Third stepping motor. A stepping motor is a device that converts the electrical pulses into discrete mechanical rotational motion of the motor shaft. This is the simplest device that can be applied to CNC machines since it can convert digital data into actual machine displacement. Fourth linear motor. A linear electric motor is an AC rotary motor laid out flat. The same principle used to produce torque in rotary motors is used to produce force in linear motors. Fifth is feedback device. In order to have a CNC machine operating accurately the positional values and the speed of the axis need to be constantly updated. Two types of feedback devices are normally used. First is positional feedback device and second is velocity feedback device. First we look at positional feedback devices. There are two types of positional feedback devices linear transducer and for direct positional measurement and rotary encoder for angular or indirect linear measurement. Linear transducer as I have seen a linear transducer is a device mounted on the machine table to measure the actual displacement of the slides in such a way that backlash of screw motors etc could not cause any error in the feedback data. So linear transducer is majorly used for direct positional measurement. If you have rotary encoder, rotary encoder is a device mounted at the end of the motor shaft or screw to measure the angular displacement. Second type of feedback is velocity feedback device. The actual speed of the motor can be measured in terms of voltage generator 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. Sixth is 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 slides, the spindle rpm, the feed rate, the power programs etc. So figure 3 shows the display unit for CNC. Write down some of the applications of the CNC. CNC machines are widely used in the metal cutting industry and are best used to produce the following types of products. Parts with complicated contours, parts requiring close tolerance and or good repeatability, parts requiring expensive jigs and fixtures if produced on conventional machines, parts that may have several engineering changes such as during the development stage of a prototype, in case where human errors could be extremely costly, parts that are needed in the hurry, small batch loads or short production runs. Some common types of CNC machines and instruments used in the industry are as follows. Grinding machine, lathe or turning center, milling or machining center, turret press and punching machine, wire cut electro discharge machine also called as EDM, grinding machine, laser cutting machine, water jet cutting machine, electro discharge machine, coordinate measuring machine, industrial robot, references, computer numerical control of machine tool and CNC programming. Thank you.