Multi-Tasking CMM Software
October 1, 2008
These days the requirements for coordinate measuring machine (CMM) metrology devices have expanded well beyond touch-probe inspection using automated CMMs. In addition to an array of devices, there also are numerous applications such as reverse engineering, hard-probing, noncontact scanning, laser tracking and digital tool building, using both portable and stationary types of devices.
For the most part, software solutions for these varied tasks have been specific to the type of task, the device type, the equipment OEM and other factors. Another variable is the various means of product definition to be used for inspection such as CAD (computer-aided design) or blueprint drawings. Also, the input of data from the myriad of CAD and CAM (computer-aided manufacturing) systems used to define product, and in the case of reverse engineering, the output to a variety of CAD systems to which data is to be sent, weighs heavily on the metrology software.
Device TypesThere are many types of digital coordinate measurement devices, which tend to have a number of things in common as well as substantial differences.
Probably the most relevant software requirement for automated machines such as the prolific direct computer control (DCC) coordinate measuring machines is the need to create a program that will operate the device throughout its calibration, alignment and inspection probing.
The primary software need for manual devices such as manual CMMs, portable CMM arms and laser trackers, is to prompt the user through steps of manual probing and then use the data-at least partially or fully real-time-to solve measurement of features and allow comparison to CAD or blueprint nominal values. Both the automated and manual processes require “crunching” of the data and output of an inspection report.
For reverse engineering both methods often require control of the data gathering and a certain degree of converting measured data to a CAD model. A lot of reverse engineering is performed totally offline with data or point clouds that were gathered in separate earlier operations. However, there are numerous advantages to performing all reverse engineering tasks live during the data gathering stage.
As with all industries, there are a number of competitors making families of devices that are very similar in design and operation. While there are a large number of OEMs in the field, corporate acquisition has reduced the field of key players to a smaller number. These OEMs tend to promote a software solution across the board for their hardware product, and they often have their own software product that is recommended to their customers.
While most OEMs offer other software solutions from third-party companies, they usually only promote them when a potential customer specifically asks for it. In some cases, OEMs adopt one primary, third-party software and promote it as if it were their own. Either way, OEMs usually market, provide pricing, and train their sales and support personnel in one primary software.
Variety of TasksCMM software is called on for a number of uses, including basic feature-type inspection with blueprint dimensions and geometric dimensioning and tolerancing (GD&T) constraints, inspecting to a nominal CAD model and digital tool building.
A considerably different application is reverse engineering, or digitizing. The methods used for the aforementioned include hard or touch probing, or some form of noncontact method such as laser scanning or photogrammetry. A number of software development companies have emerged over the years, most of which began with a focus on one or a few of these uses. Several began with stationary CMM probing software.
In the early days the primary methodology was basic feature measuring or collection of X-Y-Z values for downstream analysis by one of many CAD systems. Many of these were developed into elaborate programming systems for automated direct computer control (DCC) CMMs. A number of software developers started as point cloud surfacing solutions focusing on reverse engineering. There also were those who came from the surveying industry. A few emerged from model-based inspection (MBI) and computer-aided manufacturing.
The result of different software solutions growing out of the aforementioned origins has been a multitude of offerings each having strengths and weaknesses vs. their competitors when applied to the varied applications.
Naturally, if the software is to be applied in a limited role for a given user, it can do quite well as long as it has been chosen because of its technical strengths. But for most companies, even if they originally began using CMM technology for a specific narrow requirement, most of them will ultimately face a wider spectrum of uses down the road.
Data InputIt appears that all industries are following the lead of aerospace and automotive sectors toward a business model based on a comprehensive product lifecycle management (PLM) approach. At the heart of this philosophy is an idea known as model based definition (MBD).
With MBD, the enterprise establishes the CAD model as the primary means of product definition. Now going far beyond simply defining the geometries of components and assemblies, a whole host of information is related in the CAD model including manufacturing details and processes and inspection criteria with GD&T and datum reference definition playing a key role.
CAD has long been used both for design and inspection, particularly for manufactured items that have complex shapes-and therefore are difficult to inspect with calipers and other hand inspection tools-and for those with tight tolerance requirements. But now CAD-based inspecting is being proven as a more efficient and effective means of quality control. It can be faster, more accurate, better for global collaboration, and less open to interpretation and dispute.
Of the numerous popular CAD platforms, CATIA from Dassault Systems and Unigraphics (now NX) from Siemens have almost a duopoly on aerospace, defense and automotive design. In consumer products, AutoCAD from Autodesk and SolidWorks from Dassault Systems are the big names. The construction equipment industry seems to gravitate toward PTC’s Pro-Engineer.
With all of these CAD systems employed and vendor bases who supply to multiple industries and manufacturers, there is a lot of crossover and, in some ways, interference between these different systems.
When considering the impact of CAM requirements, the picture gets even more convoluted. Companies needing to program CNC milling machines and other digitally controlled manufacturing process such as EDM, laser cutting and welding, waterjet, composites processes and robotics, all need to use the CAD model as the foundation for programming their equipment for these processes.
Since there are at least as many CAM systems as there are CAD systems, moving the data from one format to another is a common requirement. If not controlled and monitored, things can go wrong translating from one CAD system to another or between CAD and CAM systems.
These days, CAD and PLM suppliers are trying to promote the idea that the only way to ensure there are no problems is to do all design, manufacturing and all elements of PLM with one system from one software development company. This is arguable because an enterprise that controls and monitors the process with basic and simple procedures can avoid problems.
InteroperabilitySoftware that can import directly from native CAD models greatly minimizes the problems that can arise through double-translation steps of “neutral” industry standards such as IGES and STEP. With these standards, CAD is translated one time out of the native system, and a second time into the system in which it is going to be ultimately used.
A truly interoperable CMM software can import directly from all of the major CAD native formats. It also brings them in accurately, organized in layers and colors of the native system, and can handle large CAD models of both parts and assemblies. Increasingly, CMM software imports and employs GD&T data from the native file, making for a fully compliant MBD process.
As manufacturers move toward MBD, CMM software that includes a full-powered CAD system within it has the capability to effectively import, manage, and if necessary, correct any problems with the CAD model definition.
Reverse EngineeringA lot of reverse engineering is done with point cloud data sets gathered from some type of metrology system and later imported into a reverse engineering software. There it is partially worked before going to another CAD system for further manipulation into the final product. The more complex the subject part, the more difficult this becomes.
Parts with hard edges and primitive features-for example, planar elements, holes, cylindrical, spherical, conical and sharp edges-can take hours to extract the discreet elements from dense point clouds containing noise, inaccuracy and ambiguity between features. For these situations, live reverse engineering with full-powered reverse engineering and comprehensive CAD and solid modeling capabilities in the CMM software, working live in conjunction with the metrology hardware can be an efficient and accurate method.
Also, a combination of hard probing and high-volume data scanning can work better than scanning alone. It makes it easier, faster and more accurate for reverse engineering sharp features, edges and transitions.
One Software for AllThere are a number of benefits realized by companies that adopt a common, full-capability CMM software platform company-wide. Foremost is the cost savings from training and supporting a single system. Another is a marked improvement in process control when the common software platform is incorporated with understandable, repeatable, in-house procedures.
When a company establishes a cohesive approach across the board, the related handling of product definition, acquisition, analysis and reporting of data are greatly streamlined, providing the entire enterprise with the means to maintain a useful knowledge base as well.
All of these benefits are complemented by a reduction in acquisition costs, greater flexibility of personnel within skill categories, and improved collaboration with both customers and suppliers.
Finally, it is easier to troubleshoot metrology issues when there is a well-known and established single system controlled by a common process.
When considering a CMM software for the varied needs of today’s manufacturing, those involved in the evaluation should consider the many aspects of how the software will be used and should test each use as performed by the software they are considering. Q
Quality OnlineFor more information on CMM software, visit www.qualitymag.com to read these articles:
- “CMM Software Solves Scanning Problems”
- “It’s Not Just CMM Software”
- “Managing CMM Software Uncertainties”