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Tools to simplify CMM programming.

Tools to simplify CMM programming

Five years ago, you needed a college-trained programmer to laboriously program a direct computer controlled (DCC) coordinate measuring machine (CMM). This highly skilled person needed to be versed in FORTRAN or BASIC programming languages, but not necessarily manufacturing. In fact, he or she may well have been hired away from a bank.

Thus, the people who needed the measurement information were not directly in control of its acquisition. As a result, the data was not always as useful as it could have been because programmers didn't always have direct experience with the fundamental methods and objectives of dimensional measurement.

Today, all that's changed. With a week's training, the QA professional or production person can become totally familiar with powerful geometric-measurement programs. After a few months experience with a DCC CMM, these manufacturing people can become "power users" and inhouse consultants to others who need to use this measuring system.

The software toolbox

Measurement software has evolved from a laborious programming language into an application package of modular tools readily accessible by hierarchical menu or graphics-based operator interface systems. If the right tool isn't in the "toolbox,", the user can usually build one. (Or convince the software manufacturer to create it and provide it to all users in their next software revision.)

These changes have occurred so rapidly that many current CMM users don't know how powerful and easy-to-use the current generation of software is; even those using the newest software typically use only a small portion of it.

The best CMM software today is an easily recognizable collection of tools - with a tool just right for each job. Whether or not a user makes use of the right tool for his task depends on how well his toolbox is organized.

Tools versus


Before looking at the organizing principles of programmable software for DCC CMMs, we should acknowledge another class of user-friendly software typically supplied with popular tabletop CMMs. Rather than provide the user with tools for creating measurement programs, it supplies generic measurement routines. Want to measure the distance between two circles? Just select the circle routine and follow screen prompts; it's that easy.

Routine-specific software makes it possible for workers who have never seen a CMM to make productive measurements on their very first session. The only drawback is that the vast potential of the CMM is limited to those routines supplied with the software. Although a good software package may supply upwards of 30 different measurement choices, if it does not offer a particular measurement routine you need, there is little you can do about it. Yes, a clever operator can work around this problem by combining tools, but this exposes a potential for error, and often just isn't possible.

A nonspecific geometric measurement program, on the other hand, contains a wide assortment of geometric shapes and forms already defined by algorithms in the software. Combining these forms, the user can construct task-specific templates to measure anything he or she wants.

Total freedom is not without its problems. With a geometric-measurement program, someone has to create the program before a part can be measured. Almost anyone can use that program, once it has been created, but to create it requires a certain level of software skill and fundamental understanding of measurement and geometry.

Companies used to hire computer programmers and tried to teach then dimensional measurement. With the toolbox approach, the part programmer no longer needs to be skilled in esoteric computer languages. Now, the more he or she knows about measurement, the better. A person off the shop floor with a solid foundation in measurement skills can write functional CMM part programs after a week or two of training. After six months, he or she will be considered a skilled part programmer and a valuable assets to the company. (Most companies train two programmers at a time so that they can back each other up.)

The toolbox as shipped

To program a part, the toolbox user does not have to be able to write computer code and memorize a vast array of symbols and syntaxes. Instead, he or she selects subroutines (tools) from menus or by pointing to graphic symbols. A new part measurement program goes together by assembling a series of tools, much like a child's erector set. You don't need a college education to program a part for the first time.

Software toolboxes vary from vendor to vendor. Although some are far better than others, they all have one thing in common - a logical structure. The operator's understanding of that organizational structure can make the difference between programming a complex part in a week or an hour.

Five drawers in the toolbox

A highly functional geometric measurement toolbox should contain at least five drawers - three basic tools for collecting and formatting, tolerancing, and presenting measurement data, and two additional drawers with support tools for math and communications (i.e.; networking). Drawer 1 - Geometric tools. In this most basic drawer are tools for defining part features to be measured, starting with simple two-dimensional lines and planes and working up to complex three-dimensional cylinders, cones, spheres, and profile curves. There are few 3-D features so complex that they cannot be constructed with the tools provided. The geometric phase of programming can be conducted at the CMM, at a CAD station, or at a desk with an off-line computer. Drawer 2 - Tolerancing tools. Once the CMM has collected its measurement points, the computer is used to transform this data stream into inspection information to be compared to the part's nominal dimensions and tolerances. This comparison serves as a map for determining potential manufacturing problems and optimizing a specific manufacturing process. Available options include normal geometries, true position, form tolerancing, orientation and hybrid types of tolerances from mixing and matching available tolerancing tools. Drawer 3 - Presentation tools. Once features have been toleranced, the part programmer must decide how the data will be presented for maximum usefulness. How will it be grouped? Will it be displayed, printed, or both? Do we want a steady stream of raw data on part features, or are we looking for concise real-time exception reports on features that are or will soon be out of tolerance? The options are extensive and may be used by anyone - programmer or not - who understands the fundamentals of measurement and statistical process control. Drawer 4 - Communications tools. This first supplemental drawer deals with data-networking tools. It provides means to ship data to another computer for display or analysis, share data with a CAD system, or control a pick-and-place robot to move parts to and from the CMM.

In the past, sending data to and from other computers was a laborious formal-programming task. Today, thanks to significant work in writing post processors and the popularity of the dimensional measuring interface specification (DMIS), most CMM manufacturers supply DMIS post processors with the program itself, and their selection is as easy as choosing an item from a menu. Drawer 5 - Math tools. In the math drawer are tools to automatically perform everything from simple arithmetic to special calculations, like finding the volume of a complex structure such as an injection mold for a perfume bottle. Many of these canned math operations are supplied by the software vendor, are menu selectable, or can be created by the operator. Some vendors issue expanded sets of math tools with every new revision of their product.

The idea of math tools is to provide the user with tools that can be used right away. The programmer should not have to read a book on differential equations to be able to determine the intersection of two spheres. The trick is to make mathematical concepts easy to use and stick them in the math drawer.

Continuous improvement

These are the basic drawers, but sometimes a user has a better idea of how his tools should be organized. Some software allows users to create their own drawers and arrange their software tools in more readily available sets to solve frequently encountered problems.

"Continuous improvement", the corporate goal of many QA programs, is being achieved by applying new and powerful computer technology. Today's operator interface has been radically simplified with such tools as mice, light pens, icons, touch screens, and interactive color graphics. Multitasking computers allow the simultaneous writing of programs, measuring of parts, calculating of real-time statistics, coordinating of loading/unloading, and the generation of off-line programs. The best of today's software is being written in a modular fashion to make possible the adding of new improvements quickly, such as the performing of complex contour measurements. User friendly subsets of routine-based software are being nested into easy-to-use toolbox programs for desktop CMMs as well as DCC CMMs.

Five years ago, the college-grad programmer could do just about anything he or she wanted with a CMM if he or she was an expert software engineer. Today's power users of toolbox CMM programs are "measurement-smart", shop-floor people who can accomplish 80 percent or more of what the older programmer could do and in a fraction of the time. By bringing control of the CMM to the shop floor, the CMM software toolbox now makes the goal of continuous improvement attainable.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:coordinate measuring machines
Author:Tackes, Dave
Publication:Tooling & Production
Date:May 1, 1990
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