## Working in Off-line Mode: Introduction

The off-line version of PC-DMIS is designed to allow the user to prepare and debug part programs without using a CMM. The ability to program off-line has become increasingly important over the last several years. Users of CMM's have become more aware of the fact that, in order to fully realize their investments in CMMs, their equipment must be used to measure parts, not write programs to measure parts.

CMM manufacturers' first attempts at adding off-line programming capabilities involved cumbersome, specialized text editors. These products, although of limited use, spurred user interest in off-line programming. Driven by this interest, several CAD vendors developed products that allowed users to generate part programs using CAD models.

Although these products were vastly superior to text editors, they had one major disadvantage --cost. Since each CMM vendor has their own specific measurement language or languages, which were constantly changing or in some cases being replaced, the expense of developing and maintaining these products put them out of the reach of all but a few well-financed users.

This situation brought about the development of the DMIS specification, a generic CMM language. DMIS allowed CAD vendors to develop part programming packages that were targeted toward a single language instead of many, greatly reducing their costs. These savings were passed on to their customers and off-line part programming became a viable option for a large group of CMM users. However, there was still one problem. What about CMM users whose CAD vendors did not support and did not plan to support off-line part programming?

Although many main frame CAD vendors, driven by major customers, have introduced DMIS extensions to their products, PC based CAD vendors with their diverse customer bases have shown little interest in this area. Many CMM users, particularly small shops, use PC based CAD systems exclusively. PC-DMIS brings off-line programming capabilities to this group.

With PC-DMIS, programmers using standard IGES models, which are supported by virtually every CAD vendor, can generate part programs on an inexpensive PC or PC clone without going near a CMM. These part programs can then be used to drive any CMM either running PC-DMIS or supporting the DMIS specification.

The techniques for programming off-line are much the same as those used for programming on-line. However, as might be expected, the methods used for qualifying probes, taking measurements and debugging programs differ from those used in the on-line version. This section describes PC-DMIS'S off-line programming techniques.

The main topics in this section include:

- Prerequisites

- Off-line Probes

- Setting Probe Depth

- Measuring Features Off-line

- Executing and Debugging Part Programs Off-Line