Direct Numerical Control
Encyclopedia
Direct numerical control (DNC), also known as distributed numerical control (also DNC), is a common manufacturing
term for networking CNC machine tools. On some CNC machine controllers
, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case the program is stored in a separate computer and sent directly to the machine, one block at a time. If the computer is connected to a number of machines it can distribute programs to different machines as required. Usually, the manufacturer of the control provides suitable DNC software. However, if this provision is not possible, some software companies provide DNC applications that fulfill the purpose. DNC networking or DNC communication is always required when CAM
programs are to run on some CNC machine control.
, HP, Prime
, DEC
or IBM
type computers running a variety of CAD/CAM software. DNC companies offered machine tool links using rugged proprietary terminals and networks. For example, DLog offered an x86 based terminal, and NCPC
had one based on the 6809. The host software would be responsible for tracking and authorising NC program modifications. Depending on program size, for the first time operators had the opportunity to modify programs at the DNC terminal. No time was lost due to broken tapes, and if the software was correctly used, an operator running incorrect or out of date programs became a thing of the past.
Older controls frequently had no port capable of receiving programs such as an RS232 or RS422 connector. In these cases, a device known as a Behind The Reader or BTR card was used. The connection between the control's tape reader and the internal processor was interrupted by a microprocessor based device which emulated the paper tape reader's signals, but which had a serial port connected to the DNC system. As far as the control was concerned, it was receiving from the paper tape unit as it always had; in fact it was the BTR or Reader Emulation card which was transmitting. A switch was frequently added to permit the paper tape reader to be used as a backup.
or OS/2
which could be linked in to existing networks using standard protocols. Customers began migrating away from expensive minicomputer and workstation based CAD/CAM toward more cost-effective PC-based solutions. Users began to demand more from their DNC systems than secure upload/download and editing. PC-based systems which could accomplish these tasks based on standard networks began to be available at minimal or no cost. In some cases, users no longer needed a DNC "expert" to implement shop floor networking, and could do it themselves. However, the task can still be a challenge based on the CNC Control wiring requirements, parameters and NC program format.
To remain competitive, therefore, DNC companies moved their offerings upmarket into DNC Networking, Shop Floor Control or SFC, Manufacturing Execution Systems or MES
. These terms encompass concepts such as real-time Machine Monitoring, Graphics
, Tool Management, Traveler Management and Scheduling
. Instead of merely acting as a repository for programs, DNC systems aim to give operators at the machine an integrated view of all the information (both textual and graphical) they require in order to carry out a manufacturing operation, and give management timely information as to the progress of each step. DNC systems are frequently directly integrated with corporate CAD/CAM, ERP
and Computer-aided Process Planning CAPP systems.
. Many DNC systems offer support for these protocols. Another protocol is DNC2 or LSV2 which is found on Fanuc controls. DNC2 allows advanced interchange of data with the control, such as tooling offsets, tool life information and machine status as well as automated transfer without operator intervention.
is one prominent attempt to augment the existing world of proprietary systems with some open-source, industry-standard protocols and XML schema
s and an ecosystem of massively multiplayer app development and mashups
(analogous to that with smartphone
s) so that these long-sought higher levels of manufacturing business intelligence
and workflow automation can be realized.
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
term for networking CNC machine tools. On some CNC machine controllers
Control theory
Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...
, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case the program is stored in a separate computer and sent directly to the machine, one block at a time. If the computer is connected to a number of machines it can distribute programs to different machines as required. Usually, the manufacturer of the control provides suitable DNC software. However, if this provision is not possible, some software companies provide DNC applications that fulfill the purpose. DNC networking or DNC communication is always required when CAM
Computer-aided manufacturing
Computer-aided manufacturing is the use of computer software to control machine tools and related machinery in the manufacturing of workpieces. This is not the only definition for CAM, but it is the most common; CAM may also refer to the use of a computer to assist in all operations of a...
programs are to run on some CNC machine control.
1950s-1970s
Programs had to be walked to NC controls, generally on paper tape. NC controls had paper tape readers precisely for this purpose. Many companies were still punching programs on paper tape well into the 1980s, more than twenty-five years after its elimination in the computer industry.1980s
The focus in the 1980s was mainly on reliably transferring NC programs between a host computer and the control. The Host computers would frequently be Sun MicrosystemsSun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
, HP, Prime
Prime Computer
Prime Computer, Inc. was a Natick, Massachusetts-based producer of minicomputers from 1972 until 1992. The alternative spellings "PR1ME" and "PR1ME Computer" were used as brand names or logos by the company.-Founders:...
, DEC
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
or IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
type computers running a variety of CAD/CAM software. DNC companies offered machine tool links using rugged proprietary terminals and networks. For example, DLog offered an x86 based terminal, and NCPC
NCPC
NCPC may refer to:* National Capital Planning Commission, a U.S. government agency that provides planning guidance for Washington, D.C* National Counterproliferation Center, the primary organization within the U.S...
had one based on the 6809. The host software would be responsible for tracking and authorising NC program modifications. Depending on program size, for the first time operators had the opportunity to modify programs at the DNC terminal. No time was lost due to broken tapes, and if the software was correctly used, an operator running incorrect or out of date programs became a thing of the past.
Older controls frequently had no port capable of receiving programs such as an RS232 or RS422 connector. In these cases, a device known as a Behind The Reader or BTR card was used. The connection between the control's tape reader and the internal processor was interrupted by a microprocessor based device which emulated the paper tape reader's signals, but which had a serial port connected to the DNC system. As far as the control was concerned, it was receiving from the paper tape unit as it always had; in fact it was the BTR or Reader Emulation card which was transmitting. A switch was frequently added to permit the paper tape reader to be used as a backup.
1990s and beyond
The PC explosion in the late 1980s and early 1990s signalled the end of the road for proprietary DNC terminals. With some exceptions, CNC manufacturers began migrating to PC-based controls running DOS, WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
or OS/2
OS/2
OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 " line of second-generation personal...
which could be linked in to existing networks using standard protocols. Customers began migrating away from expensive minicomputer and workstation based CAD/CAM toward more cost-effective PC-based solutions. Users began to demand more from their DNC systems than secure upload/download and editing. PC-based systems which could accomplish these tasks based on standard networks began to be available at minimal or no cost. In some cases, users no longer needed a DNC "expert" to implement shop floor networking, and could do it themselves. However, the task can still be a challenge based on the CNC Control wiring requirements, parameters and NC program format.
To remain competitive, therefore, DNC companies moved their offerings upmarket into DNC Networking, Shop Floor Control or SFC, Manufacturing Execution Systems or MES
MES
- In business :* Manufacturing Execution Systems, the intermediary between a business system such as ERP and a manufacturer's plant floor control equipment* Marconi Electronic Systems, a defunct company of the United Kingdom...
. These terms encompass concepts such as real-time Machine Monitoring, Graphics
Graphics
Graphics are visual presentations on some surface, such as a wall, canvas, computer screen, paper, or stone to brand, inform, illustrate, or entertain. Examples are photographs, drawings, Line Art, graphs, diagrams, typography, numbers, symbols, geometric designs, maps, engineering drawings,or...
, Tool Management, Traveler Management and Scheduling
Scheduling (production processes)
Scheduling is an important tool for manufacturing and engineering, where it can have a major impact on the productivity of a process. In manufacturing, the purpose of scheduling is to minimize the production time and costs, by telling a production facility when to make, with which staff, and on...
. Instead of merely acting as a repository for programs, DNC systems aim to give operators at the machine an integrated view of all the information (both textual and graphical) they require in order to carry out a manufacturing operation, and give management timely information as to the progress of each step. DNC systems are frequently directly integrated with corporate CAD/CAM, ERP
Enterprise resource planning
Enterprise resource planning systems integrate internal and external management information across an entire organization, embracing finance/accounting, manufacturing, sales and service, customer relationship management, etc. ERP systems automate this activity with an integrated software application...
and Computer-aided Process Planning CAPP systems.
Special protocols
A challenge when interfacing into machine tools is that in some cases special protocols are used. Two well-known examples are Mazatrol and HeidenhainHeidenhain
Dr. Johannes Heidenhain GmbH is a privately owned enterprise located in Traunreut, Germany that manufactures mechatronic measuring devices for length and angle....
. Many DNC systems offer support for these protocols. Another protocol is DNC2 or LSV2 which is found on Fanuc controls. DNC2 allows advanced interchange of data with the control, such as tooling offsets, tool life information and machine status as well as automated transfer without operator intervention.
Machine monitoring
One of the issues involved in machine monitoring is whether or not it can be accomplished automatically in a practical way. In the 1980s monitoring was typically done by having a menu on the DNC terminal where the operator had to manually indicate what was being done by selecting from a menu, which has obvious drawbacks. There have been advances in passive monitoring systems where the machine condition can be determined by hardware attached in such a way as not to interfere with machine operations (and potentially void warranties). Many modern controls allow external applications to query their status using a special protocol. MTConnectMTConnect
MTConnect is a manufacturing industry standard to facilitate the organized retrieval of process information from numerically controlled machine tools. The initiative began as a result of lectures given by David Edstrom of Sun Microsystems and Dr...
is one prominent attempt to augment the existing world of proprietary systems with some open-source, industry-standard protocols and XML schema
XML schema
An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself...
s and an ecosystem of massively multiplayer app development and mashups
Mashup (web application hybrid)
In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services...
(analogous to that with smartphone
Smartphone
A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...
s) so that these long-sought higher levels of manufacturing business intelligence
Business intelligence
Business intelligence mainly refers to computer-based techniques used in identifying, extracting, and analyzing business data, such as sales revenue by products and/or departments, or by associated costs and incomes....
and workflow automation can be realized.