Numerical Control Machine(NC)
Form of programmable automation.
Mechanical actions of machine tool are controlled by
The program is in form of alphanumeric data.
After a job is finished the program of instructions can be
changed to process a new job.
Numerical Control Machine(NC)
Reduces non productive time
Reduces manufacturing lead time
Greater manufacturing flexibility
Improves quality control
High investment cost
High maintenance effort.
Higher utilization of NC
To overcome the shortcomings of the NC machines CNC machines
CNC machines are the NC machines whose MCU is based on the micro
computer rather than the hardwired controller.
Storage of more
than one part
Common types of CNC
CNC Lathe machine
CNC Milling machine
CNC Drilling machine
CNC Grinding machine
CNC Laser cutting machine
Water jet cutting machine
Electro discharge machine
Reduce lead time
Reduce scrap rate
Reduced non productive time
• Parts needed in a hurry
• Parts with complicated contours
• Parts requiring expensive jigs and fixtures
• Parts those have several engineering changes
• Cases where human errors can be extremely costly
• Parts requiring close tolerance or good repeatability
Components of CNC
Dc brushless motor
Digital pulse is converted into rotary
It is an open loop system
A stepper motor is a type of DC motor which has a full rotation
divided in an equal number of steps.
There is stator winding and a permanent magnet at the centre
When electric current is passed through winding it starts acting
as an electromagnet and the permanent magnet moves.
The position of the rotor is controlled by the attractive and
Control is achieved at low cost
High torque at startup and low speed
Can operate in open loop control system
Low torque at high speed
Requires a dedicated control circuit
Should not be used for high performance or
high load applications.
A servomotor is a simple electrical motor controlled
with the help of servomechanism.
Servo motors are functional with the sensor feedback.
The input to its control is signal either in the analog or digital form
Servo motors are primarily used where speed, power , noise level
as well as velocity and positional accuracy.
DC Brush Servo motors:
The brush refers to the brushes which passes the electric current to the rotor ,
the rotating part of the motor. In DC Servo motor each coil is angularly displaced
from one another so when the torque drops off from one coil it automatically
switches to the another coil as to produce the maximum torque. This switching is
done by the brushes and a commutator present in the motor.
AC Servo motors:
Its physical construction is similar to that of the DC Servo motor but there are no
magnets in the AC Servo motor. But both the rotor and the stator are
constructed from coils. These are capable of delivering very high torque at very
high speed. There are no brushes in this type of motors which means they are
Motor is controlled by a feedback signal generated by comparing output signal and the reference
Reference input signal is applied to the system and compared with output signal of the system and
thus a third signal is generated by feedback system.
This third signal acts as input signal to the device. This input signal to the device is present as long
as there is a logical difference between reference input signal and output signal of the system.
After achieving the desired output there will be no longer logical difference between the input
signal and the output signal of the system.
Now the feedback signal is not enough to produce further output until the next reference input
signal is provided.
High speed attainable
Wide variety is available
High peak torque available
Can be demagnetised
DC Servo motors
AC servo motors
High torque available
Cannot be demagnetised
Accurate position information
Added feedback component
Increased control complexity
An encoder is a device, circuit,
transducer, software program,
algorithm that converts
information from one format or
code to another, for the purposes
The recirculating ball steering mechanism contains a
worm gear inside a block with a threaded hole in it.
This block has gear teeth cut into the outside to
engage the shaft.
They convert sliding friction into rolling friction.
wear will be reduced
reliability of the system will be increased
the efficiency of ball screws may reach up to
This type of screw provide backlash-free movement
Their efficiency is same as that of ball screws.
These are capable of providing more accurate position control.
Cost of the roller screws are more compared to ball screws.
The thread form is triangular with an included angle of 90 degrees.
The rollers in this case are not threaded.
The rollers are provided with a circular groove and are
positioned circumferentially by a cage.
Recirculating roller screws are slower in operation.
They are capable of transmitting high loads with greater