Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

43.2.2 Computer Numerical Control (CNC)

 

· A computer controller is used to drive an NC machine directly.

 

· Characteristics are,

  1. - controls a single machine
  2. - located very close to machine tool
  3. - allows storage/retrieval/entry of NC programs without preprocessing of NC code

 

· Advantages of CNC,

  1. - program is only entered into memory once, so it is more reliable
  2. - the programs can be tested and altered at the machine
  3. - increased flexibility and control options on the local computer
  4. - easy to integrate into FMS systems

 

· The Background,

  1. - the problems with NC tapes were approached using DNC networks
  2. - the communication problems with DNC systems became obvious, and local computers were added to act as tape readers which would read tapes once, and play them back to the NC machine indefinitely
  3. - CNC controllers began using other storage media like magnetic tapes, and floppy disks
  4. - CNC now offers features like,
    1. - local programming,
    2. - communication over interfaces,
    3. - hard disk storage,
    4. - program simulation
    5. - etc.

 

· ASIDE: Direct Numerical Control is similar to CNC, except a remote computer is used to control a number of machines. This gives the advantage of more computer power. This approach is no longer popular, as the dropping cost of computers offsets any advantages.

 

· Some companies use proprietary NC Languages, such as the example of DYNA Mill NC code shown later

 

· These machines are often programmed by downloading NC code from a computer, or manually programming the controller computer.

 

· Future trends involve,

  1. - adaptive feed rates to increase speeds as the metal removal rate varies
  2. - tool wear detection
  3. -