Numerical control (NC) may be a kind of programmable automation during which the mechanical actions of a bit of apparatus are controlled by a program containing coded alphanumeric data. 

The information represents relative positions between a piece head and a piece part.

The work head may be a tool or other processing element, and the work part is that the object being processed.
The operating principle of NC is to regulate the motion of the work head relative to the work part and to regulate the sequence in which the motions are dole out.
The first application of numerical control was in machining, and this is often still a vital application area.
Components of an NC System A numerical system consists of three basic
components: (1) part program, (2) machine control unit, and (3) processing equipment. The part program (the term commonly utilized in machine technology) is that the detailed set of commands to be followed by the processing equipment. 
It’s the program of instructions within the NC system. Each command specifies an edge or motion that’s to be accomplished by the work head relative to the work part. a footing is defined by its x-y-z coordinates. In machine applications, additional details in the NC program include spindle rotation speed, spindle direction, feed rate, tool change instructions, and other commands associated with the operation. The part program is prepared by part programmer, someone who is acquainted with the small print of the programing language and also understands the technology of the processing equipment.
The machine control unit (MCU) in modern NC technology may be a microcomputer that stores and executes the program by converting each command into actions by the processing equipment, one command at a time.

The MCU consists of both hardware and software.

The hardware includes the microcomputer, components to interface with the processing equipment, and certain feedback control elements.

The software within the MCU includes system software, calculation algorithms, and translation software to convert the NC part program into a usable format for the MCU.
The MCU also permits the part program to be edited just in case the program contains errors, or changes in cutting conditions are required. Because the MCU could be a computer, the term computer numerical control (CNC) is commonly wont to distinguish this sort of NC from
its technological predecessors that were based entirely on hard-wired electronics.
The processing equipment accomplishes the sequence of processing steps to transform the starting work part into a completed part.
It operates under the control of the MCU per the instructions within the part program.
Coordinate System and Motion Control in NC a typical axis system is employed to specify positions in numerical control.

The system consists of the three linear axes (x, y, z) of the co-ordinate system, plus three rotational axes (a, b, c).
Most NC systems don’t require all six axes.
The simplest NC systems (e.g., plotters, press working machines for flat sheet-metal stock, and component insertion machines) are positioning systems whose locations can be defined in an x-y plane. Programming of those machines involves specifying a sequence of x-y coordinates. in contrast, some machine tools have five-axis control to shape complex work part geometries.
These systems typically include three linear
axes plus two rotational axes. These systems are related to turning operations on NC lathes.

Although the work rotates, this is often not one. The cutting path of the tool relative to the rotating workpiece is defined within the x-z plane.
In many NC systems, the relative movements between the processing tool and also the work part are accomplished by fixing the part to a worktable and so controlling the positions and motions of the table relative to a stationary or semi-stationary work head. Most machine tools and component insertion machines are supported this method of operation. In other systems, the work part is held stationary and therefore the work head is moved along two or three axes. Flame cutters, x-y plotters, and coordinate measuring machines operate during this mode.

Motion control systems supported NC is divided into two types: (1) point to-point and (2) continuous path. Point-to-point systems, also called positioning systems, move the work head (or workpiece) to a programmed location with no regard for the trail taken to urge to it location. Once the move is completed, some processing action is accomplished by the work head at the placement, like drilling or punching a hole. Thus, the program consists of a series of point locations at which operations are performed.
Continuous path systems provide continuous simultaneous control of over one axis, thus controlling the trail followed by the tool relative to the part. this allows the tool to perform a process while the axes are moving, enabling the system to get angular surfaces, two-dimensional curves, or three-dimensional contours in the work part. This operating scheme is required in drafting machines, certain milling and turning operations, and flame cutting. In machining, continuous path control also goes by the name contouring.
An important aspect of continuous path motion is interpolation, which is anxious with calculating the intermediate points along a path to be followed by the work head relative to the part.
Two common varieties of interpolation are linear and circular. Linear interpolation is employed for line paths, during which the part programmer specifies the coordinates of the start point and end point of the line similarly because the feed rate to be used. The interpolator then computes the travel speeds of the 2 or three axes that may accomplish the desired trajectory.
Circular interpolation allows the work head to follow a circular arc by specifying the coordinates of its beginning and end points along with either the middle or radius of the arc. The interpolator computes a series of small line segments. 

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