Direct Numerical Control ( DNC ) | Working Principle | Applications | ENGINEERING STUDY MATERIALS

Hello viewers, welcome to Engineering Study Materials. Today we are going to discuss about the direct numerical control. In short, we can say that if a machine tool is controlled by a computer through a set of codes, it is called as a direct numerical control. In olden days, this was the popular method of controlling the machine tools in industries. It consists of a mainframe computer that was used to control a number of the NC machines. NC machines such as a drilling machine, milling machine, reaming, boring, etc. These machines are controlled by a set of instructions by a central computer or a subcomputer which is set for the particular machines and the subcomputers are controlled by a central computer. The part programs are directly entered into the computer without using the punched tapes. In olden days, the punched tapes are used for the feeding instructions are given as an output for the machines to control the process. Nowadays, the programs are set in a set of instructions are given to the computer as an input so that it can control the NC machines. The processing and post-processing of the part program is performed in a computer itself. This enables the programmer to modify and edit the program. So, what are all the components of the DNC? First, a central computer used to control the set of instructions and bulk memory for the storage of the instructions, telecommunications lines for the communication between the subsystems or subcomputers and then machine tools such as drilling, milling, reaming, boring, lathe, etc. Functions of the DNC. Numerical control without punch tape and NC part program storage, data collection, processing and reporting to the machine or a computer and then communications using the communication lines and advantages of the direct numerical control are elimination of the punch tape, reading, great computational capability because a central computer controls all the instructions that are enabled within the system and convenience storage of the part programs. A large set of programs in various large sizes can be stored in a single central computer because the storage capabilities of the central computer is more than the punch tape and then reports on sharp performance. The performance of the individual machines can be obtained from the central computer itself without checking the individual machines by direct contact. Then, computer numerical control. CNC can be defined as a NC system for a single machine tool that uses a dedicated computer control by stored instructions in the memory so that it can implement NC functions. Then, what is a CNC machine? Simply, it is a machine that performs operations by a set of instructions by a computer so that we can do n number of operations from that. Then, this is a CNC system which consists of a machine tool table which consists of two or more screws. First one servo motor which is used to control the lead screw by moving used for moving the machine tool table from front and back and feedback transducer is present on the lead screw so that if to give the feedback of the machine tool table and the servo motor. Two servo motors and feedback transducers are present and the machine tool table is present over the top and it consists of a machine control unit an MCU. It contains DPU and CLU. DPU consists of the ROM to control the program and execute. It obtains the program and controls and then executes and RAM. It is a part program stored temporarily. Then, CLU interpolates. What is interpolate? If we provide a 10 set of instructions, it chooses the correct order of instructions and interpolates. If we want to drill a 5 mm dia hole, then we are to switch over to 5.5. It interpolates automatically without feeding instructions for the 5.5 mm dia. Just we put 5.5 as a value. Then, control the output signals and amplifier or comparator circuits. Then, the MCU is turned to program input device. First, this starts from this only. Part program is fed into the program input device that is a computer. Then, the control unit obtains the program from this and sends to the machine system. It consists of part program, program input device, machine control unit, drive system, machine tool and feedback system. Then, types of CNC machines. Based on the feedback control, it is divided into the open loop system and closed loop system. Open loop system means without boundary and closed loop system is within the boundary. And based on the motion control, it consists of positional, paraxial, continuous path system. Then, based on the power drive, hydraulic system, electric system, pneumatic system and based on the circuit technology, it consists of analog system and digital system. Based on positioning, absolute positioning and incremental positioning system. Then, based on axis, 2-axis, 3-axis, 4-axis and 5-axis. Constructional features. First, machine structure. Then, slide ways and guide ways, actuation systems, free drives and spindle drives. These are all the shown in this diagram itself. Then, comes to machine structure. Machine structure is the first load carrying capacity. Structure is the machine tool table itself. It is an example and its function is to transmit the forces to the foundation. Example, it includes bed, column and other supporting members. Slide ways or guide ways. It is used to control the line of action of the carriage or table on which the tool or workpiece is held and to absorb the static and dynamic forces. And guide ways should possess good rigidity so that it can withstand the large amount of forces. Otherwise, it will collapse and damage the entire machine. Types of guide ways are flat guide ways, V-guide ways, dovetail guide ways, cylindrical guide ways. More number of guide ways are also present because innovation takes every day. An anti-friction linear motion guide ways. Linear bearing with balls and roller guide ways. Recirculating ball bushings guide ways. And hydrostatic guide ways such as oil lubricated guide ways and air bearing guide ways. Next actuation system. Actuation system are used to convert the rotational movement into translation movement. Screw and nut that is a recirculating ball screws, recirculating roller screws and rack and pinion. Feed drives used to provide motion. They are servo motors, stepper motors, linear motors. Servo motors includes AC, DC, brushless DC. Stepper motor includes variable reluctance type, permanent magnet type and hybrid type. And then spindle drives. The function of spindle is to deliver the power to hold and to center the workpiece tool in the machine table. Spindle should be less in weight. Otherwise, it will not use to transmit the forces. The accuracy of the spindle depends on the quality of the bearings. If you provide the more quality precision bearings, we can get the perfect accuracy of the spindle drive. Then the characteristics of the spindle drive. High rotational accuracy, fast dynamic response, excellent running smoothness and compactness, high loading capacity. So this is a short video friends. If you like this video, please hit a thumbs up button and share this video to your friends to gain knowledge. And please subscribe this channel for more interesting videos. So finally, thank you for watching.