3 Open CNC Protocol Specification

3.1 Motivation for Opening A NC Architecture

We can say that we are facing a day that Machine Tools makers can integrate their equipment by freely available parts from the control systems vendors, just like Personal Computer makers, they can freely choose the parts and construct PCs with full variety. The proven reliability of the conventional CNC (Computerized Numerical Control) systems is good when the design and manufacturing are separately done. But, currently, PC based CAD system enables the simultaneous manufacturing when the PC is connected closely to the machining tools. At the same time, we can expect the cost reduction of shop floor systems using the computational power of PC not only in CAD/CAM but also in machining or status monitoring. The other words, the closeness of CNC causes some problems; vendor-dictated pricing structure, no-common interfaces, higher integration costs, and higher cost of function enlargements.

To cope with this problem, the expectation for an open CNC architecture is too big for machinery industry. It is generally said that an Open System provides capabilities and environment that enable properly implemented applications to run on a variety of the platforms from multiple vendors and interoperate with other systems applications. This implies how to open and disclose the CNC architecture which follows common vendor-neutral conventions for CNC maker, machine tool maker, software vendor, system integrators, and users.

The CNC architecture in this draft is a specification of capabilities and services that provides the interconnecting structure and definition of the interfaces among interoperating functional components. In order to open this CNC architecture, two kinds of approach are considered. One is ideal and revolutional approach which links or connects various function units under Message Based Communication Platform, another is realistic and evolutional approach which groups and structures functional units into some functional layers.

This draft recommends the latter method. The main reason is its capability to improve the legacy accumulating during past long period. We employ three functional layers as follows.

Each functional group communicates by message passing.

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The openness of CNC architecture facilitates interoperability, portability, scalability, and interchangeability and expandability on a shop floor. Interoperability will only be guaranteed by using standardized data semantics and behavioral models, communication and interaction mechanisms. Portability allows to transfer applications or enhancements which have been developed on one controller to a controller based on another platform. Scalability gives customers the freedom to increase or decrease the functionality of a system as their needs and budgets increase. Interchangeability allows to substitute one component with another due to its capabilities, reliability or performance. Expandability is a feature, which enables users and third parties to incrementally add functionality to a module without replacing it completely.

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