17-07-2014, 12:16 PM
CNC SYSTEM
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WHAT IS CNC?
– CNC may be defined as the numerical
control system where in a dedicated
programs in a computer are used to
replace some or all of its control
functions.
– In CNC the program is read once by he
tape reader as the input device & is
stored in the controller’s random access
memory.
PRINCIPLE OF OPERATION OF CNC:-
In CNC the program is read once by the tape
reader and stored in the controller’s random access
memory. When a stored program has to be executed
in the CNC machine the instruction blocks in the part
program are implemented by the micro processor
with the help of the control programs resident in ROM.
The output from the controller may be either as a
sequence of reference phase or as a binary word in
sampled data system, with the first type of system the
microprocessor helps in generate a sequence of
reference phase for each axis of motion; each phase
producing CNC small unit of motion (sum).
ADAPTIVE CONTROL:-
Adaptive control implies that he CNC system is
responsive to adapt. Itself operate at those
machining parameter which result in higher
productivity of part programmer.
so by the ADAPTIVE CONTROL below
mentioned control selection can be apply named as
ADAPTIVE CONTROL with constraints ACC.
1)Use the available spindle power to maximum.
2)Limit the deflection of the cutter.
3)Limit the cutting tool temperature.
4)Limit the vibrating amplitude of the cu
FEATURE OF CNC:-
A CNC system provides all the above functions
through with the help of software based control
principle.
1)Interpolation (Linear & Circular)
2)Tool compensation using dedicated switches.
3)Speed & feed ever ride.
4)Repeated program start for batch manufacture.
5)Minor imaging.
6)Sealing.
7)Suppression of NC block.
8)Online part programming through difficult & time
consuming
INTERACTIVE CNC:-
Programming and machine operation has been further
made easier and speedier by the following developments in
this direction.
Automatic preparation of part program with minimum
essential data input in the form of familiar words.
Easier input data definition with the help of callous,
graphical, special familiar character and multiple windows on
the screen.
Automatic tool selection according to the shape of work
piece to be machined and the machining process.
Automatic determination of machining condition such as
spindle speed, depth of cut and feed rate on the basis of
material data
Automatic geometric calculation of dimension like those of
inter section and tangent on data input from the work piece.
DIRECT NUMERICAL CONTROL :-
DNC is the first stop towards the factory of future. It is a
manufacturing system in which a central computer communicates
with the controllers of several machine tools by as direct connection
in real time. Its essential functions in addition to the earlier
mentioned NC/CNC capabilities of the machine tools are.
1) To used the memory of the central computer far working programs
meant for several NC/CNC machines. In principle programs hundred
of machines may be stored. This function includes input, output,
editing, updating, copying and erasing of programs at DNC computer.
2) To transfer or download directly the part programs from central
computer to individual machine control units of machine.
3) To provide software for processing of the above mentioned shop floor
data for management purposes. This may includes real time
rescheduling of operations on several machine
MODEM:-
It is a device which converts digital data from computer &
other DTE ( data terminal equipment) like CNC controller and
computers into signal which can be transmitted over long
distances over telephone lines. The term modem into analog
signals of light signals in case at fiber optic telephone lines. The
modem can be viewed as an interface between digital equipment
and analog line. At the sending side the modem modulates
(conditions) the digital signal making it suitable for transmission
over the line. At the receiving den it demodulates the signal and
converts it look into original digital signal for the receiving
equipment. The public service telephone lines can be thus used to
transmit data over long distances above 10 km with the help of
long haul modems. The short haul modems may of course be
used for distances within a range of 2-10 km. typical data transfer
rates (also called BAUD rate of locally available modems range
from 300 bps (bits per seconds) to 19.2 kbps.