nc cnc

1. NC & CNC

2. Numerical Control
 Numerical Control (NC) is the automation of machine
tools that are operated by programmed commands.
 It is unlike manually controlled machines which are
controlled by hand wheels, levers or mechanically
automated cams.

4. Punched Tape

5. CNC Technology
 CNC refers to how a machine controls its basic method
of movement.
 A CNC machine reads digital coded information from a
computer to move the motors and other positioning
systems in order to guide a spindle over the raw
material which is to be machined.

6. Difference between CNC and Conventional Machines
CNC Machine Conventional Machine
CNC machines can be used
continuously for long intervals and
only need to be switched off for
occasional maintenance.
Conventional machines are difficult
to operate for several hours at a
stretch. The operator has to
continuously focus on the job at
hand.
CNC machines can produce several
products, all similar and absolutely
accurate.
Accuracy of the products depends
upon skill of the operator.
Less skilled/trained persons can
operate CNC machines.
Highly skilled operators are required
to work on conventional machines.
CNC machines can be updated by
using improved software to drive
the machines.
Chances for major improvement in
the conventional machines are very
less.
One person can supervise several
CNC machines, and they can be left
to work themselves.
One person cannot operate more
than the conventional machine at a
time.

7. Classification of CNC Systems
CNC machine tool systems can be classified in various
ways such as :
 Point-to-point or contouring : depending on whether
the machine cuts metal while the workpiece moves
relative to the tool.
 Incremental or absolute : depending on the type of
coordinate system adopted to parameterise the
motion commands.
 Open-loop or closed-loop : depending on the control
system adopted for axis motion control.

8. 1. Point-to-point Systems
2. Contouring Systems
3. Incremental Systems

9. 4. Absolute System
 An absolute NC system is one in which all position
coordinates are referred to one fixed origin called the
zero point.
5. Open Loop Systems
 The term open-loop means that there is no feedback
 In open loop systems the motion controller produces
outputs depending only on its set points, without
feedback information about the effect that the output
produces on the motion axes.
 Contouring systems do not use open-loop control.

10. 6. Closed Loop Systems
 Closed-loop control continuously senses the
actual position and velocity of the axis.