DOS platforms in CNCs

Modern Machine Shop, July, 1991 by Golden E. Herrin

DOS Platforms In CNCs

A question that CNC users have ask since the introduction of CNC is "What else can I do with this computer that's running my machine?" This question is intended to inquire what commercially available software packages such as spreadsheets or word processors can be run on the CNC to extend its capability. This is a very logical question from the users viewpoint since much emphasis has been placed on the CNC being a computer based device. Until recently, the answer to this question has been "none." The CNC has been "off limits" to commercially available software packages due to the proprietary nature of its design. However, after twenty years, this condition is rapidly changing with the introduction of DOS platforms in CNCs.

To explain what a DOS platform is and why it is important, some background is necessary. DOS is the acronym for Disk Operating System and refers to IBM's operating system for personal computers. Although it originated as a proprietary operating system by IBM, it is available today in both an IBM version (DOS) and a Microsoft version (MS-DOS). Both operating systems are commonly referred to as DOS. From this common usage of DOS, the term "DOS compatible" has evolved as a term defining the software compatibility aspect of IBM clones. To have a computer that is "DOS compatible" means that there is a vast number of existing software packages to choose from. Total compatibility, of course, is subject to matching up specific hardware with the software requirements for features such as type of graphics adapter, memory size and computer speed.

A DOS platform in a CNC consists of appropriate hardware plus a purchased or licensed copy of DOS software. The hardware may consist of a complete personal computer embedded in the CNC or a custom hardware module designed by the CNC builder. Access to certain CNC functions like slide positions, probe data, tool data and alert files are necessary if the full capability of DOS based programs such as statistical analysis packages or quality control packages are to be fully utilized. Additionally, it is desirable to have the capability to pass part program data between DOS and the CNC.

In order to fully utilize the capability of DOS and take advantage of the many available DOS programs, the platform must have all of the basic elements of an IBM compatible personal computer. These include adequate non-volatile mass memory in the form of a hard disk or equivalent, a minimum of 1mb of Random Access Memory (RAM), appropriate video graphics capability and a color monitor. For communication to the DOS platform, a full keyboard and a floppy disk unit are required as well as communication ports directly into the DOS section so as not to tie up the CNCs communication ports. The DOS platform should also run independently from the basic CNC system (in background mode) so that part machining can occur simultaneously with other functions being performed in DOS.

The thing that makes the DOS platform so desirable is that it provides "something for everyone"--the user, the machine tool builder and the CNC builder. For the user, it provides a platform in the CNC where DOS compatible programs can be run. For example, a frequent question asked by end users: can the CNC provide statistical analysis on parts that have been machined? Since most CNCs can probe, gather and save part data, why not let the CNC perform a trend analysis on this data? In the past, this capability was only possible in an off-line computer or a cell controller.

The benefits are equally rewarding for the machine tool builder. For example, the DOS platform may very well provide a convenient place in the CNC for the machine tool builder to run development software for the interface logic. Many CNCs require an additional DOS compatible personal computer for this development work. When the machine is in the debug mode on the shop floor, it is often necessary to carry a portable personal computer to the shop in order to perform the debugging operation. With the DOS platform in the CNC, development is made easier.

For the control builder, the DOS platform provides a CNC unit with a much broader scope. From the control builder's view point, there are always more features and capabilities being requested than can ever be designed into a CNC's proprietary software. The control builders, therefore, must use their available engineering resources to develop the features that will sell the most controls. The features of a specific CNC unfortunately does not satisfy the needs of every customer and when a custom feature is requested, it often requires reinventing software that already exists in a similar DOS form.

For a CNC utilizing a DOS platform, existing or emerging software modules from outside the CNC environment may be brought in and with either minor or no modification be made to function as an effective upgrade to the control. For example, a CNC that does not support "shop floor programming" may be upgraded by installing a commercially available personal computer version of an off-line programming system in the DOS platform. To this can also be added the appropriate post processor.