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Information about DNC BY B M NAMAZI

Published on February 6, 2008

Author: namazibasheer

Source: authorstream.com

DIRECT NUMERICAL CONTROL(DNC) MACHINES:  DIRECT NUMERICAL CONTROL(DNC) MACHINES B M NAMAZI S2/MTECH MACE Slide2:  Machine Tools Schematic of a Machine Tool 2 axis - Table moves along x & z only 2.5 axis - Table moves EITHER along x & y OR along z 3 axis - Table can move simultaneously along x, y & z 4 axis - Tool can be moved from vertical 5 axis - Tool has 2 orientation axes Slide3:  Numerical Control (NC) The machine tool is controlled electronically instead of manually A part program is read in from paper tape This contains coded instructions for the machine tool to move the table and/or tool to adjust the tool speed to turn on/off coolant Like machine code, the instructions for an NC machine tool are not very meaningful to people APT is the equivalent of Assembly Language and very popular for writing part programs Slide4:  Brief Chronology of NC 1948 Numerical Control (NC) idea conceived by John Parsons; taken up by USAF 1952 MIT demonstrated the first prototype 1959 Automatically Programmed Tools (APT) language first used at MIT ca 1968 Direct Numerical Control (DNC) developed ca 1970 Computer Numerical Control (CNC) developed ca 1980 Hybrid DNC/CNC Graphical NC (GNC) Slide5:  DNC Direct Numerical Control Distributed Numerical Control DNC Satellite System Hybrid DNC/CNC Slide6:  Direct Numerical Control (DNC) DNC connects a number of NC machines to a central computer Tape reader dispensed with Part-programs delivered directly from central computer Still no memory on machines Slide7:  Direct Numerical Control Slide8:  Distributed Numerical Control Slide9:  DNC Satellite System Since all communication between central computer and NC machines must be performed in real-time satellite computers are often used to reduce the burden on the central computer’s processor Slide10:  Hybrid DNC/CNC CNC machines configured in a DNC topology Often referred to simply as DNC these days since DNC in its original form is no longer used When used in this sense DNC stands for “Distributed Numerical Control” Slide11:  WAYS OF CONVERSION TO DNC There were two ways in which a standard NC machine could be converted into a DNC machine Behind the Tape Reader (BTR) Special Machine Control Unit (MCU) These approaches typify two attitudes which can be taken towards technological developments Slide12:  Behind the Tape Reader (BTR) Least flexible approach but cheapest Tape reader replaced by comms lines Conventional NC controller retained Two storage buffers added to controller One to receive blocks from central computer One to send instructions on to m/c tool Slide13:  Special Machine Control Unit(MCU) More flexible and costly Conventional NC controller replaced Special MCU speeds up communication Faster interpolation without loss of accuracy MCU soft-wired for greater flexibility Control functions more easily altered Slide14:  Advantages of Hybrids Advantages over pure DNC If central computer fails the machines can carry on working Complete part-programs can be downloaded from central computer – no need to wait for each instruction Local processing power and memory Advantages over pure CNC Elimination of tape input in CNC Complete part-programs can be downloaded from central computer – no need to load them locally Improved communications on shop-floor and between shop-floor and production control

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