This document discusses the components and workings of CNC machines. It begins by explaining numerical control machines and their evolution into CNC machines, which are controlled by a microcomputer rather than hardwiring. The main electrical components of CNC machines are stepper motors and servo motors. Stepper motors move in discrete steps while servo motors use feedback control. Mechanical components include recirculating ball screws and roller screws which convert sliding motion to rolling motion for precision positioning.

1. CNC Machine & Its
Components

2. Numerical Control Machine(NC)
Form of programmable automation.
Mechanical actions of machine tool are controlled by
program.
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.

3. Numerical Control Machine(NC)
Advantages
Reduces non productive time
Reduces manufacturing lead time
Greater manufacturing flexibility
Improves quality control
Reduced inventory
Disadvantages
High investment cost
High maintenance effort.
Part programming
Higher utilization of NC
equipments

4. CNC Machines
To overcome the shortcomings of the NC machines CNC machines
evolved.
CNC machines are the NC machines whose MCU is based on the micro
computer rather than the hardwired controller.
Elements of
CNC machines
are
Part program
Machine Control
Unit
Machine tool
Features of
CNC machines
are:
Storage of more
than one part
program
In-process
compensation
Improved
programming
and operating
features
Adaptive control
adjustments

5. Common types of CNC
machines
CNC Lathe machine
CNC Milling machine
CNC Drilling machine
CNC Grinding machine
CNC Laser cutting machine
Water jet cutting machine
Electro discharge machine

6. Advantages
Higher accuracy
Reduce lead time
Higher flexibility
Reduce scrap rate
Reliable operation
Consistent quality
Reduced manpower
Increased productivity
Reduced non productive time

7. Applications
• 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

8. Components of CNC
Electrical components
Mechanical components

9. Electrical components
Stepper motor
Servo motors

10. Stepper MotorStepper Motor

11. Dc brushless motor
Digital pulse is converted into rotary
motion.
It is an open loop system

12. Operating principle
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
of windings.
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
repulsive forces.

14. Advantages
Control is achieved at low cost
High torque at startup and low speed
Simple construction
Can operate in open loop control system
Low maintenance

15. Disadvantage
Low torque at high speed
Requires a dedicated control circuit
Should not be used for high performance or
high load applications.

16. Servo Motor

17. Servo Motors
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.

18. Servo
motors
DC brush
servo motor
AC servo
motors

19. 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
maintenance free.

20. Working Principle
Motor is controlled by a feedback signal generated by comparing output signal and the reference
input signal.
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.

21. Advantages
Low Cost
Smooth rotations
High speed attainable
Wide variety is available
High peak torque available
Disadvantages
Thermally inefficient
Require maintenance
Can be demagnetised
DC Servo motors

22. AC servo motors
Advantages
High Performance
Maintenance Free
High torque available
Cannot be demagnetised
Accurate position information
Disadvantages
Expensive
Added feedback component
Increased control complexity

23. Encoders
An encoder is a device, circuit,
transducer, software program,
algorithm that converts
information from one format or
code to another, for the purposes
of standardization.

24. ENCODERS
INCREMENTAL ABSOLUTE
ROTARY AND
LINEAR

25. Mechanical components
Recirculating ball screw
Planetary roller screws
Recirculating roller screws:

26. Recirculating ball screw

27. 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.

28. Advantages
wear will be reduced
reliability of the system will be increased
the efficiency of ball screws may reach up to
90%.

29. Roller screw
Roller screw

30. Roller screw
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.

31. Roller screw
Planetary
roller screw
Recirculating
roller screw

32. Planetary roller
screw

33. These are capable of transmitting high
load at fast speed.
There is no axial movement of the rollers
relative to the nut.
The rollers are threaded with a single
start thread.

34. Recirculating roller screw

35. 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
accuracy