Explain the basic elements of CNC machines with a diagram

9.B] With the help of a block diagram, explain the basic elements of CNC machines


Computer Numerical Control (CNC) is one in which the functions and motions of a machine tool are controlled by means of a prepared program containing coded alphanumeric data.

Components of CNC:

A CNC machine tool following units in its construction,

  1. Input device
  2. MCU or machine control unit
  3. Machine tool
  4. Driving System
  5. Feedback devices
  6. Display Unit
CNC machines
Block Diagram of CNC Machine Tool

Input Devices:

In-put devices are the devices used to enter the part program into the machine tool.

Universal Serial Bus (USB), ethernet communication, Tapes, and recording devices can be used as input devices.

  1. Machine Control Unit:
  • The machine control unit (MCU) is a microcomputer that stores the program and executes the commands into actions by the machine tool.
  • The MCU consists of two main units: the data processing unit (DPU) and the control loops unit (CLU).
  • The DPU processes the data from the part program and provides it to the CLU which operates the drives attached to the machine leadscrews and receives feedback signals on the actual position and velocity of each one of the axes.
  • A driver (dc motor) and a feedback device are attached to the leadscrew.
  • The CLU consists of the circuits for position and velocity control loops, deceleration and backlash take up, and function controls such as spindle on/off.

2. Machine Tool:

  • The machine tool could be one of the following: lathe, milling machine, laser, plasma, Coordinate measuring machine etc.
  • Machine tools actuated as per the program through various mechanical driving and feeding mechanisms.
  • Machine tools perform the intended task over the workpiece.

3. Driving system:

  • A drive system essentially is made up of amplifier circuits, drive motors and ball lead screws.
  • Commonly used types of electrical motors include DC Servo motors, AC servo motors, Stepping motors, and Linear motors

4. Feedback devices:

  • For the accurate operation of a CNC machine, the positional values and speed of the axes need to be continuously updated.
  • In order to perform this task Positional feedback devices and velocity feedback devices are used.

5. Display Unit:

  • A device that ensures interaction between the machine operator and the machine is called a display unit.
  • It displays the current status of the operation such as the spindle RPM, running part program, feed rate, the position of the machine slide, etc.

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