Mechatronics 1 2

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Fundamentals of NC
Advantages of NC
Classification of NC
PTP- Contour
NC-CNC
Incremental – absolute
Open loop – closed loop
Punched Card

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Mechatronics 1 2

  1. 1. Mechatronics Module 1
  2. 2. • Fundamentals of NC • Advantages of NC • Classification of NC – PTP- Contour – NC-CNC – Incremental – absolute – Open loop – closed loop • Punched Card
  3. 3. Manufacturing Systems Evolution • Construction of simple production machine started in 1770 • Fixed automatic mechanisms and transfer lines for mass production came along at this century • Introduction to Numerical control NC in 1952 • The logical extension of NC – CNC • Industrial robots were developed simultaneously with CNC • First commercial robot in 1961 • 1969 Mechatronics – • FMS with CAD / CAM
  4. 4. Fundamentals of Numerical Control • Fundamentals of Numerical Control
  5. 5. Definition – EIA Electronics Industries Assoc. • Numerical Control 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 the data.
  6. 6. NUMERICAL DATA (NC CODE) MANUFACTURING OPERATOR NUMERICAL CONTROLLER Drive Control PROCESSED PART MACHINE UNIT 6
  7. 7. Types of Numerical Control • Conventional Numerical Control (NC) – Data is sent to the machine tool by means of punch cards or tapes. The reader at the machine performs no calculations or interpolations. • Computer Numerical Control (CNC) – The idea of computer numerical control is to position a computer right at the machine tool. 7
  8. 8. Computer Numerical Control (CNC) 8
  9. 9. • Part Program- Numerical data on a punched tape. • The block contains , in coded form , all information for processing a segment of work piece like Segment length, cutting speed, • NC replaces the manual actions of the skilled operator.
  10. 10. • Part Programmer V/s Skilled operator. • APT – Automatically Programmed Tool • BLU- Each unit corresponds to the position resolution of axes of motion referred to Basic Length Unit. • BLU is also known as ‘increment size’ or ‘bit weight’. •
  11. 11. • The part dimensions are expressed in part programs by integers • To calculate position command in NC, the actual length is divided by the BLU value. • To move 0.7 inch in positive X direction , with BLU =0.001, the position command is X+700
  12. 12. • Axis of motion – An axis in which the cutting tool moves relative to the work piece.XYZ • Machine tools- drilling,milling,lathe • Rotary motions also possible.
  13. 13. NC machine parts • MCU – Data Processing Unit • To decode the information received from tape, process it, and provide data to CLU – Control Loops Unit. • Operated Drive attached. • Machine tool
  14. 14. Advantages of NC • • • • • First NC- 1952. Accuracy- Measuring Time 70-80 % Time wasted on measurements Tolerance improved. A Further saving of time is achieved while passing from one operation to another during the machining of the work space. • Rate of production decreases in conventional method
  15. 15. • Contour cutting in 3 D or 2D can not performed by manual operation • Two Hand wheels required for this operation
  16. 16. CNC - Disadvantages • High initial investment • A long preparation time for each production series. • Inflexibility of the process. Machine is planned to make a certain fixed cycle of operation. If the part configuration changed , The machine adjustment must be rebuilt or altered. • A big stock of parts is required for the process.
  17. 17. • • • • • NC in Flexible Manufacturing System Production in low quantity Eg . Aircraft Machines should be economical. When a new product required , only the part program has to b chgange.
  18. 18. Advantages of NC 1. A Full flexibility ; a part pgm is needed for producing a new part 2. Accuracy is maintained through the full range of speeds and feeds. 3. A shorter production time 4. Easy adjustment of the machine. Less time than other manufacturing methods 5. The possibility of manufacturing a part of complicated contour. 6. Need for highly skilled & Experienced labor is avoided 7. The operator has free time
  19. 19. Disadvantages of NC • A relatively high cost • More complicated maintenance- Special maintenance crew is desirable. • Highly Skilled & properly Traned part programmer is needed •
  20. 20. Classification of NC • According to type – Point to point / contouring • According to Structure – NC/ CNC • According to programmed method – Incremental / absolute • According to type of control loops – Open loop / closed loop
  21. 21. Point to point
  22. 22. • Drilling machine • Work piece is moved along axis of motion until center of hole is drilled is exactly beneath the drill • Drill is automatically moved to the work piece, hole is drilled , and the drill moves out in a rapid traverse speed.
  23. 23. Contouring systems
  24. 24. • In countering or continuous-path systems, the tool is cutting while the axis of motion are moving. • Eg. milling machine •
  25. 25. Interpolator • Interpolator contained in the DPU of contouring systems provide the proper velocity commands for each axis.
  26. 26. Straight Cut Systems • PTP machine equipped with milling tool.
  27. 27. NC & CNC • NC- Hard ware based • CNC- software based • The digital control in NC employs voltage pulse. • 1 pulse = BLU (NC) • Pulses to actuate motors. – Stepper- open loop – DC motor – closed loop
  28. 28. • 1 bit = BLU (CNC) • Simplest hardware configurations – emulates hardware based NC and transmit output pulse. • 1 bit =1 pulse =BLU • The main difference in the operation between NC and CNC is in the way that the punched tape is read. – NC – read 1 block and cut – CNC – store complete data , stored in memory before cutting starts.
  29. 29. Incremental / Absolute
  30. 30. Absolute - Advantages • With an incremental system , each time the work is interrupted the operator must restart the part pgm and repeat the entire operation • Dimensional data can change at any time. • One reference point
  31. 31. Incremental - Advantages • Inspection of the part pgm is easy. Sum of position commands must be zero • The performance of the incremental system can be checked by a closed-loop tape. This is a diagnostic punched tape which test the various operations and performance of the NC Machine • Mirror image programming is facilitated with incremental systems. The sign of the corresponding position commands is changed from + to - . No new calculation required for the position
  32. 32. Open Loop / Closed loop

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