Users of tactile metrology devices such as CMMs and arm type measurement systems routinely program them offline. This has been going on for years.

On the other hand, the norm for vision and multisensor measurement systems is on-line programming. This long-standing state of affairs is more a matter of custom than utility, and it is done at great cost in terms of both lost productivity and increased measurement systems costs.

Becoming CAD-Centric

Wilcox Associates’ PC-DMIS Vision allows users to program offline so measurement equipment can be used simultaneously to measure other parts. Source: Wilcox Associates

To program vision equipment offline, all you need is software that can import the CAD model of the part and interact with it in a virtual environment for vision and multisensor system programming. Instead of teach and learn programming with an actual part, the programming process takes place using a virtual part.

The end results that the programs generate using either of these two procedures are nearly identical. The big difference is that while the programmer was developing programs on the virtual machine, the actual measurement machine was measuring actual parts -- a two-fold improvement in productivity. In addition, programming in the virtual mode is faster because all of the nominals and a great deal of other important information about the part are part of the CAD model.

Virtual Viewing: Vision system users who have been programming their systems on-line for many years say that they really appreciate being able to navigate within a live view of the part to adjust things like the zoom, magnification and lighting. They will be pleased to learn that some vision and multisensor software is capable of generating realistic simulations of all these capabilities so that what is done intuitively at the machine can also be done in the simulated environment.

Then there is lighting, which is one of the most difficult vision measurement parameters to simulate. Even so, some of today’s vision software has come a long way and can now realistically simulate top, bottom and ring light illumination. The best of these lighting algorithms are very good and research is on going to further improve them.

Everything Offline: With computer simulation, vision/multisensor system programmers can rotate the part, adjust the magnification, verify the point density, change sensors from vision to laser or tactile, simulate and adjust the lighting and perform a complete offline simulation of the measurement process to determine measurement cycle time. Then they only need to make a few machine-specific adjustments to the program on the measurement device.

Final Adjustments: Even these final adjustments at the machine can be computer automated. Some software is capable of cycling the program through all of the views so the programmer can quickly decide whether or not they want to adjust any of the settings, particularly lighting, at each critical point in the measurement process.

This "autotuning" capability has an important secondary benefit. Should it be necessary to shift a measurement program to a different machine, it is a simple matter to run the program through this autotuning sequence to adapt the program to the new measurement system quickly.

No Part Needed: During product development, it is not unusual to see four weeks allocated for design, four weeks to manufacturing and three weeks to quality assurance. When design or manufacturing take longer than anticipated, quality assurance is left with the unenviable task of having to make up for lost time.

One of the not-so-obvious benefits of offline vision and multi-sensor measurement system programming is that you don't actually need a part to do it. You only need a CAD model. As a result, the measurement folks don’t have to worry as much about being at the tail end of the product development cycle. With offline programming, users create measurement programs while the parts are being manufactured. This eliminates any delays in validating parts and ensures that QA does not slow down product development.

Case in Point

Recently a European manufacturer of small metal components converted four of its vision measurement systems to CAD-based programming and operating software. This same manufacturer bought three additional licenses of the software for offline programming. Since this company is closely associated with the style-conscious fashion industry, the product development burden on this company is frequently heavy. During the new product introduction crunch time, an over-dependence on the use of the vision systems for programming can conflict with production measurement requirements.

The software the customer purchased for offline programming is identical to the software they use on their vision measurement systems with one exception: It doesn’t have a machine interface. Now the manufacturer can pre-program all its measurement sequences offline, including sophisticated two-step zooming operations. The fine-tuning of machine-specific adjustments takes only a few minutes per part and the bulk of the vision system’s time is spent productively measuring parts.

The bottom line for this manufacturer is that, in addition to improving its vision-system programming throughput, the company has also substantially increased its measurement capacity. During times of heavy product development, instead of using three machines for programming and one for measurement, all of its systems are busy measuring parts.