| ( 1 ) Different components related to CNC
machine tools |
| Any CNC machine tool essentially consists of
the following parts: |
A part program is a series of coded instructions
required to produce a part. It controls the movement of the
machine tool and on/off control of auxiliary functions such
as spindle rotation and coolant. The coded instructions are
composed of letters, numbers and symbols. |
| ( 1.2 ) Program input device: |
The program input device is the means for part
program to be entered into the CNC control. Three commonly used
program input devices are punch tape reader, magnetic tape reader,
and computer via RS-232-C communication. |
| ( 1.3 ) Machine Control Unit: |
The machine control unit (MCU) is the heart
of a CNC system. It is used to perform the following functions:
- To read the coded instructions.
- To decode the coded instructions.
- To implement interpolations (linear, circular,
and helical) to generate axis motion commands.
- To feed the axis motion commands to the
amplifier circuits for driving the axis mechanisms.
- To receive the feedback signals of position
and speed for each drive axis.
- To implement auxiliary control functions
such as coolant or spindle on/off and tool change.
|
A drive system consists of amplifier circuits,
drive motors, and ball lead-screws. The MCU feeds the control
signals (position and speed) of each axis to the amplifier circuits.
The control signals are augmented to actuate drive motors which
in turn rotate the ball lead-screws to position the machine
table. |
CNC controls are used to control various types
of machine tools. Regardless of which type of machine tool is
controlled, it always has a slide table and a spindle to control
of position and speed. The machine table is controlled in the
X and Y axes, while the spindle runs along the Z axis. |
| ( 1.6 ) Feed Back System: |
The feedback system is also referred to as
the measuring system. It uses position and speed transducers
to continuously monitor the position at which the cutting tool
is located at any particular instant. The MCU uses the difference
between reference signals and feedback signals to generate the
control signals for correcting position and speed errors. |
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