What Are the Functions of Computer Numerical Control CNC?

laser cutting machine
Read : What is CNC (Computer Numerical Control)? Advantages, Limitations, Applications
Comparison between CNC and DNC - Advantage and functions of DNC


CNC is designed to perform many functions which either difficult or impossible to perform by a NC machine. Some important function of CNC are:
  • Machine Tool Control
  • In-process compensation
  • Improved programming and operating features
  • Diagnostic

Machine Tool Control

Controlling the machine tool is the primary function of a CNC. It includes the conversion of part program instruction into machine tool motions. This conversion is done through a computer interface and servo system.

What is CNC (Computer Numerical Control)? Advantages, Limitations, Applications

cnc machine

CNC (Computer numerical control) System is similar to NC system, and it uses stored program to perform an operation instead of using Punched tapes. In old CNC machines the part program is initially entered similar to the conventional NC machine. Punched tape reader is the common device to input part program. In NC machine punched tape is needed to cycle through a reader for every workpiece, while in CNC the tape reader is used only once for the first loading of part program. Entered part program in first workpiece is stored in computer memory. It provides additional flexibility and computational capability over conventional NC machine. In latest CNC, the part program is created and then input it into machine by using CAD/CAM software.

Basic Component of Numerical Control NC Technology

component of NC
Read: What is Numerical control? Applications, Advantages, Limitation

An NC system consists following components.
  • Program instruction
  • Machine control unit (MCU)
  • Machine controlled process (tool)
The relation between this three component is represented above

Program instruction

Program instruction is served as the input into the controller unit. It is a detailed step by step instruction which tells the machine tool what/how to do. Each instruction specify the position and movement of machine tool. This detailed set of command is coded into some type of input medium which is then interpreted by the controller unit. The most common method of inputting instruction is punched tapes.

What is Numerical control? Applications, Advantages, Limitation

NC machine

What is NC machine?

Numerical control is defined as the form of programmable automation in which numbers letters and symbols control the operation. This instruction is designed to do a particular job. NC machines has capability to change the program for each job ie when job changes the program instruction is also changed. It is easier to change the program instruction than to modify the production equipment. This flexibility reduces the overall production cost.

What Are The Temperature Limitations For Refrigeration Cycle (Reversed Carnot)?

coefficient of performance of refrigerator

Even though the reversed Carnot cycle is impossible, here it is used to show the temperature limitation of the Refrigeration cycle.
Coefficient of performance of refrigeration system that working on reversed Carnot cycle is
(COP)R =T1/(T2-T1 )
T1 = Lower temperature (temperature to be maintained in the refrigerator)
T2 = Higher temperature (temperature of cooling water/air available for heat rejection)

Why Is Carnot Cycle Not Possible In Heat Pump And Refrigerator?

reversed Carnot cycle pv and Ts diagram

Read: COP of air refrigerator working on reversed carnot cycle with PV and Ts diagram

In working of refrigerator, the term Carnot cycle represents the reversed Carnot cycle. As we know that, between the fixed temperature limits, a heat engine operating on Carnot cycle give highest possible efficiency. Similarly, a refrigerator working on reversed Carnot cycle give the highest possible coefficient of performance. Even though no heat engine and refrigerator used Carnot cycle. This is because that the isentropic process of Carnot cycle requires a high speed of air while the isothermal process of Carnot cycle requires extremely slower speed. This large variation in speed of air is simply not possible.