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DNC Concepts | ||||||
Topics: Why network machines? What is unique about machines? DNC Implies use of Server Computers Networking Star Networks "Single-drops" Buss Networks "Multi-drops" Wireless DNC Networks Why DNC?: Simply put, you need to connect your shop floor with your engineering and business systems. Or briefly, as manufacturers move from functional structure to Process-oriented structure they "decentralize" to gain flexibility and quality. Originally Distributed Numerical Control (DNC) was used to save time and money over manual methods of loading programs, or using punched tape. Today DNC is an essential element of CIM and production logistics. Networking eliminates errors, and gives all machines a unified way to access files. Network security features keep your files safe. Programs in CNC memory can be saved easily and rapidly, so you will not loose edited files. DNC is constantly improving, and you now have more affordable options than ever. You do not have to buy new machines, or buy an expensive "DNC" options from the machine manufacturers to gain the improvements provided by DNC. Advanced Digital Research Inc. specializes in providing networking for all types/brands of machines.
Hardware Evolution PC manufacturers are no longer providing RS232 ports and Parallel printer ports on PCs. So applications supporting serial ports and parallel printers require 3rd party hardware which duplicates the interface capabilities. USB The Universal Serial Bus is intended to connect printers, scanners, keyboards and mice as well as hard drives to the PC. DB9, DB25 serial ports and DB25 printer port connectors are not provided on new PC, because of the popularity of USB. USB is capable of delivering data at a high rate. RS232 ports connected via USB tend to have limitations compared to the serial ports that used to be on the motherboard or provided in a ISA or PCI slot. The problem is that USB is far slower to respond to interrupts, making "Drip-feed" impossible. PCI bus slots PCI Express has displaced the 32bit PCI bus. PCI-E uses a very high speed serial protocol, providing high speed data and low cost due to smaller connectors. Multi-port Serial adapters requiring PCI slots are loosing popularity. Windows Microsoft Windows is the defacto standard in manufacturing. DOS was popular due to its simplicity but it lacks graphics and networking. Windows 2000/XP/VISTA are far superior to earlier versions of Windows, which did not support "Plug and Play" and were much harder to configure. These newer Operating systems are derived from the "NT" kernel, and the serial communications capability starting wiht Windows 2000 has remained virtually unchanged. This means new and old application can continue to use RS232 serial ports. Networking Machines: DNC means connecting the company database with machines. You might dedicate a personnel computer to each machine in your shop, or you might support all of your machines from one central computer. ADR can provide you with software and hardware applicable to both of these choices. When many machines are attached to one PC there are two common network topologies commonly used: star and bus. You must choose a network topology and then wire your shop, we are here to help you do it right. Drip-FeedWhen the NC program is too large to fit into the CNCs memory, it can still be run, by the PC feeding the data to the CNC as it needs it. Not all CNC can do this. The problem is to keep the CNCs buffer full of data without ever going empty, because if the CNC is "starved for data" the part being machined could be ruined. Care must be taken to insure that, no corrupted data is ever processed by the CNC, or data is lost. The PC must remain "ON-LINE" during the execution of the program, turning the PC off, or "Suspending" to save power would be a disaster.
Another popular Star network is based on 10BaseT Ethernet. An Ethernet Hub (switch) is used as the central point and twisted pair wires carry data at 10Mbit/sec. Some machines can directly attach to Ethernet others require adapters. Ethernet is referred to as a peer-to-peer protocol because there is no dedicated network manager. FTP (based on TCP/IP) is standard procedure for accessing DNC server files. ADR's LanTap Ethernet adapter handles the DNC procedures required by the CNC.
Wireless Ethernet DNC Networks Wireless DNC is gaining popularity. Wireless Ethernet can be used to connect a wired Ethernet system to wireless nodes via "Access Points". The Access points translates the Ethernet packets into radio signals, bridging the gap between the wired subnets. The benefits of eliminating the wires gets offset somewhat by new problems related to interference of the radio signals. Care must be taken to prevent blocking the radio signals with metal, or operating RF devices such as microwave ovens. Wireless DNC operates by the "line of sight" rule, the sender must "see" the receiver in order to work. Wireless DNC signals can bounce off metal or walls, a condition called "multi-pathing", which can stop communication. Data security is also an important consideration, because of the "broadcasting" of data. Nearby wireless notebook computers/PDAs could be listening in or joining your network. Blue Tooth - An alternate to Ethernet wireless is "BlueTooth" wireless. Blue Tooth is intended as a means to connect computer components such as mice, keyboards, printers and SERIAL PORTs to a PC. Notebook computers are popular in manufacturing due to the ability to freely move about. With BlueTooth serial ports at the CNC the operator does not have to phyiscally connect a wire from the CNC to the notebook, eliminating grounding problems and tripping on the cable. The distance limitation of 100 meter, means this technology requires PCs near to the CNC. Bluetooth is a frequency hopping Spread Spectrum radio, operating at 2.4GHz. Bluetooth was designed specifically for replacing wires of all kinds; Ethernet was designed as a datalink protocol for computer networks. Bluetooth makes your PC software "think" you are using wired COM ports, so your DNC software works with Bluetooth without any change. Behind the scenes, Bluetooth Generic Access Profile (GAP) handles discovery and establishment of links between devices that are unconnected, and Bluetooth Serial Port Profile (SPP) defines how to set-up Virtual Serial Ports and connect two Bluetooth enabled devices.
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