About CNC Controllers
CNC controllers are devices that control machines and processes. They range in capability from simple point-to-point linear control to highly complex algorithms that involve multiple axes of control. CNC controllers can be used to control various types of machine shop equipment. These include horizontal mills, vertical mills, lathes and turning centers, grinders, electro discharge machines (EDM), welding machines, and inspection machines. The number of axes controlled by CNC controllers can range anywhere from one to five, with some CNC controllers configured to control greater than six axes. Mounting types for CNC controllers include board, stand alone, desktop, pendant, pedestal, and rack mount. Some units may have integral displays, touch screen displays, and keypads for control and programming.
Industrial communications options for CNC controllers include ARCNet, CANBus, ControlNET, Data Highway Plus, DeviceNet, Ethernet 10/100 Base-T, parallel, PROFIBUS, SERCOS, Universal Serial Bus (USB), serial (RS232, RS422, RS485), and web-enabled. Communications language choices include bitmap, conversational, DXF file, G/M codes, Hewlett Packard graphics language, and ladder logic. A bit map (often spelled "bitmap") defines a display space and the color for each pixel or "bit" in the display space. Conversational language is a higher level, easy to learn programming tool. It performs the same functions as the standard G-code commands. Drawing eXchange Format (DXF) file that was created as a standard to freely exchange 2 and 3 dimensional drawings between different CAD programs. It basically represents a shape as a wire frame mesh of x, y, z coordinates. G-code is the programming language for the Computer Numerically Controlled (CNC) machine tools that can be downloaded to the controller to operate the machine. M-code is the standard machine tool codes that are normally used to switch on the spindle, coolant or auxiliary devices. Hewlett Packard Graphical Language (HPGL) was originally created to send 2 dimensional drawing information to pen plotters, but has since become a good standard for the exchange of 2 dimensional drawing information between CAD programs. Ladder logic is a programming language used to program programmable logic controllers (PLC). This graphical language closely resembles electrical relay logic diagrams.
CNC controllers have several choices for operation. These include polar coordinate command, cutter compensation, linear and circular interpolation, stored pitch error, helical interpolation, canned cycles, rigid tapping, and auto-scaling. Polar coordinate command is a numerical control system in which all the coordinates are referred to a certain pole. The position is defined by the polar radius and polar angle. Cutter compensation is the distance you want the CNC control to offset for the tool radius away from the programmed path. Linear and circular interpolation is the programmed path of the machine, which appears to be straight or curved, but is actually a series of very small steps along that path. Machine precision can be remarkably improved through such features as stored pitch error compensation, which corrects for lead screw pitch error and other mechanical positioning errors. Helical interpolation is a technique used to make large diameter holes in workpieces. It allows for high metal removal rates with a minimum of tool wear. There are machine routines like drilling, deep drilling, reaming, tapping, boring, etc. that involve a series of machine operations but are specified by a single G-code with appropriate parameters. Rigid tapping is a CNC tapping feature where the tap is fed into the work piece at the precise rate needed for a perfect tapped hole. It also needs to retract at the same precise rate otherwise it will shave the hole and create an out of spec tapped hole. Auto scaling translates the parameters of the CNC program to fit the work piece.
Features common to CNC controllers include alarm and event monitoring, behind tape reader, diskette floppy storage, tape storage, zip disk storage, multi-program storage, self diagnostics, simultaneous control, tape reader, and teach mode.
http://www.cnc-academy.com/cnc-programming-articles/cnc-programming-articles.htm
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