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Programming CMMs

 

Off-line programming tools keep CMMs free for inspection tasks

 

By Patrick Waurzyniak
Senior Editor

       

Off-line programming software tools for CMMs allow manufacturers to increase measurement capacity and throughput by programming CMMs, probes, and fixtures before parts are made.

With off-line tools, manufacturers increase part inspection, boosting time-to-market and enhancing CMM productivity. By inspecting parts more quickly without interruptions for programming, manufacturers can meet their production goals and boost measurement accuracy with newer off-line programming tools that now include simulation capabilities within the CMM programming environment.

Some of the latest software packages feature simulation capabilities incorporated into offerings from both OEMs of CMM hardware and also from third-party software developers. In addition, as portable articulated arms have proliferated in the measurement field in recent years, the increased number of less-expensive portable CMMs on the shop floor leads to greater need for effective off-line programming solutions.

Programming off-line means CMM users essentially off-load the programming chores of CMMs in order to free up expensive CMMs to perform measurement inspection duties. "Off-line programming offers the same advantages that you'd have on a CNC machine tool, in that you're not tying up that precious piece of hardware to write programs," notes Kevin Legacy, applications engineering manager, Carl Zeiss IMT Corp. (Minneapolis), regarding off-line programming. "CMMs are being used to make money, meaning inspecting parts and keeping the machine tool running.

"Typically today though, that's not the case," Legacy says. "Most people do the programming on the CMM, and that makes it less efficient. It means they can't measure as many parts and they can't make the best decisions, so for all the same reasons that you program off-line for CNC cutting machines, you want to do the same things for CMMs. The majority of programming today is still done online, but certainly our users would like to see it move more towards the type of thing that happens in a CAM world, where everything is programmed off-line."

Most programming solutions for CMMs feature CAD-based systems that often employ the widely used Dimensional Measuring Interface Specification (DMIS), an ANSI standard which last year was updated with DMIS Part 2. The updated DMIS includes object-oriented technology aimed at offering true plug-and-play capabilities to both new and existing CMMs.

Collision detection through simulation can greatly aid shop-floor users of CMM equipment by detecting collisions between probes and workpiece components in advance, while performing off-line programming duties, notes John Wootten, software manager, LK Metrology Systems Inc. (Brighton, MI, and Derby, UK).

"With off-line programming, two issues are important--one is collision detection, the ability to detect collisions between the probe and the component when you're programming off-line, so you can iron out issues in the part program before you get to the CMM," notes Wootten. "Another important issue is the ability to simulate the CMM itself, and to be able to work with both perfect data or imperfect data, and we can simulate imperfect data."

The upcoming release of LK's Camio Studio CMM programming software will enable users to simulate potential collisions between the CMM probes and workpieces. The simulation capabilities, which had been used by LK programmers as a development tool, will be added to LK's Camio Studio Version 4 release, notes Wootten, and users also will be able to utilize the newest version of DMIS, which adds many enhanced commands for programming scanning capabilities in machines.

To ease the task of programming CMMs, Zeiss' latest version 3.8 of its Calypso CMM software recently added a new module called Calypso Planner specifically aimed at performing off-line programming chores. Equipped with extensive simulation capability, the Calypso Planner module offers an off-line version of inspection for creating measurement plans.

"In the most basic sense, off-line programming allows a user to create a CMM inspection program either with or without the CAD model," Zeiss' Legacy explains. "Typically today, everybody thinks that if you're going to create a program offline and don't have a part, that means I need to have a CAD model. But with Planner, you can create programs with or without the CAD model, so it allows the user to create a program off-line and not tie up his machine."

Working without a CAD model, the basic tools of Calypso allow users to define the areas they want to inspect. "As an example, let's say an operator wanted to measure the size of a hole and location of the hole," Legacy says. "There's some basic information that the system needs when there's no CAD model--the software would need to know the diameter of the hole, where is it located from a datum, and maybe the angle of the hole relative to the datum. Once the operator inputs that information to create his off-line program, Calypso begins to build the CAD model for him. So without a CAD model, the software will build one for him, or with a CAD model it simply uses the model to help make the measurement program."

Programming parts with CAD models is easier, he adds, since users just click on data on the model, and programs like Calypso quickly extract all the necessary information. "With our Planner software, you are planning a measurement task separately from running the machine," Legacy says. "What most people do with an off-line programming product is they allow someone to create a program off-line, and in its most basic form. Beyond the basic form, Planner has a model that allows either selecting all of our tooling from the probe library, just like you do with a machine tool or a robot, or build the tooling, if it's a custom set of tools that you need. We call this the Probe Simulation, which allows the operator, once he's created his programs, to test it on the part to make sure there are no collisions by testing it with the same tool he will use when he runs it on the CMM."

Simulations offer users visual tools, but Legacy notes that Zeiss' Calypso software actually prevents any collisions because of a clearance area built around parts. "The reality is that it's a great visual tool, and customers are always asking if we have a probe simulation tool because they have grown up programming CNC machines with tools that can simulate the probe," notes Legacy. "But our software builds a 'clearance skin' around the part, like a snakeskin. Calypso will not enter that skin except to take measurements, so you don't really need simulation--it's more of a visual tool, because there will not be crashes."

An updated PC DMIS Version 3.6 due soon from Brown & Sharpe (North Kingstown, RI) will add to the CMM programming environment's simulation capabilities. Developed by Wilcox and Associates (Danville, CA) for its metrology partner Brown & Sharpe, PC DMIS has a separate off-line programming module, according to Wilcox' Mike Wilson. "From an off-line programming standard, we've added many new CMM models into the application that allow users to more accurately model the machine which the part program is intended for," Wilson says. "With this new version of PC DMIS, we've also added simulation support for all of the extra accessories like the tool rack and probing."

While DMIS remains the predominant neutral data exchange standard for CMMs, many of the latest CMM programming software packages offer very wide-ranging data-handling capabilities with import/export of most CAD/CAM file formats. Third-party developer Verisurf Software Inc. (Anaheim, CA) has a full line of CAD-based CMM programming software that runs under both CNC Software Inc.'s (Tolland, CT) Mastercam software, which leads all CAM packages in installed number of seats, and now is offered as well under the CATIA V5 CAD/CAM package from software developer Dassault Systemes (Paris) and IBM Corp. (Armonk, NY).



Off-line programming can be performed with Zeiss' Calypso Planner software module, which helps users create measurement plans
 
Verisurf's VeriProbe software enables users to automate programming of CMMs, including those specifically for programming CNC machines for machine-tool probing, notes Scott Knoche. "Our new Verisurf V5 inspection product runs in CATIA V5, and because part of the strength of our software is our device interface application [Verisurf Device Interface], we could adapt it pretty easily to other CAM systems," Knoche notes. "Right now, it runs under Mastercam with an inspection system also in CATIA V5, but if the industry supported it or people came to us with requests of another platform, it wouldn't be very hard for us to adapt to another platform."       

With Verisurf software, users can perform off-line programming at an engineering station away from the CMM, Knoche notes. "There is a bit of time and effort required in programming, so it's good that you don't have to take CMMs off-line," he adds. "There are all kinds of inspection software systems--it's a mixed bag. We do off-line programming, plus on - line systems for use with CMMs, laser trackers, portable articulating arms, and new technology like indoor global positioning systems."

Although Verisurf supports the DMIS standard, the company takes a different approach than many others in the CMM software market, notes Verisurf president Ernie Husted. "We support DMIS, but we're not a big cheerleader of DMIS," Husted states. "We're taking the CAM market approach. Machine tools have their own controls and you have a CAM system that supports all the controls, and people buy software to program off-line for parts. CMMs went the other way. Each control has its own software so you have hundreds of different software packages out there. We're trying to change that, and do off-line programming as you would for a machine tool. We can post out of DMIS, or we can post out of G code. We could post out to machine tool probing, or different flavors of DMIS, because every CMM has had their own flavor."

Portable articulating arms and inspection equipment like laser trackers becoming more commonplace has made it possible to do more for a lot less investment, Husted notes. "The portable equipment arms and the trackers are becoming more accurate--almost CMM accuracy now--for less money, and they're more portable," Husted notes, "so in the programming that we do, we take the CAD model and pick the features, and create a plan. DMIS is more like a syntax. You have to learn the syntax, learn the rules, you have to be a code writer. In machine tools, that would be like a G-code writer. We don't have G code anymore, the posts handle that."

Support of the STEP-NC standard, the IGES format, and working under Mastercam means Verisurf can handle most of the CAD model data encountered by users, he adds. "Mastercam supports STEP-NC. That's a thing for the future and it'll support probably half the parts out there." The software also allows direct reads of major formats including CATIA, Pro/Engineer, and Unigraphics formats, plus AutoCAD, SolidWorks, SolidEdge, Parasolid, and other industry formats, so data interoperability does not pose a barrier.

With manual devices like portable arms propagating, some off-line programming actually may become less necessary, as software like Verisurf can handle the data input of inspections on the shop floor for the user. "Manual devices are now getting to be almost as accurate as CMMs," Knoche says, "and especially if you're doing one-off inspection, as on a tool where you're only going to make one part, you can get through the inspection of the part in the time that it would take you to program it, so why write a program?

"With our off-line programming system, you can use that same system for directing an operator through the use of a manual device for inspection, so instead of telling the machine to go here and take a point, it tells the operator on the screen with targets and identifiers, 'go here and take a point.' It draws targets and leads him through the inspection. In fact, you can even have it reject his point if he doesn't do it properly, or if he doesn't measure something properly. It'll lead him through the whole thing. We really try to get away from programming, where a guy just picks things off the CAD model. When you zoom in on features, the software memorizes the zooms and rotates--you don't have to take images--it's all done automatically in the software.



Simulations in programs like LK's Camio Studio software allow users to visualize CMM equipment and probes with the workpiece before completing inspections.

"We're finding that companies like that for process control, because you've got a setup inspection routine and you're going to do it repeatably every time. It brings your inspectors into this repeatable process, and reporting is done the same way every time. When you get to the end of the inspection, it automatically feeds the database."

As portable arms' accuracies improve, customers increasingly are interested in affordable equipment for the shop floor. "CMMs are coming down and the arms are going up," Husted says. "The accuracies are all less than a thousandth now on these arms, and that handles probably 90% of the tolerances out there."

 

This article was first published in the May 2004 edition of Manufacturing Engineering magazine. 


Published Date : 5/1/2004

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