Case Studies: New Territory With Vision Inspection
By integrating 3-D CAD-based vision inspection with conventional tactile probing, Accu-Tech Inc. (Detroit), a contract measurement lab, has broadened the range of parts it can measure with unimpeachable accuracy. In addition, this approach has improved measurement productivity, allowing the company to gain a competitive edge and provide its customers with faster turnaround on critical parts. What made this possible was a new kind of coordinate measuring machine (CMM)-like vision software (PC-DMIS Vision), which can be used on both conventional vision and multi-sensor measurement equipment.
Accu-Tech Inc. is an ISO 17025 mechanical testing lab accredited by A2LA. Customers rely on the lab to perform complex measurements, provide trustworthy third-party verification of part dimensions, and develop custom PC-DMIS measurement programs that operators will use in production manufacturing environments.
“Contract inspection is a very competitive business,” says president Ed Drozdowski. “Since I started Accu-Tech Inc. 10 years ago, I haven’t raised my rates once. Instead, I am continually looking for ways to improve our productivity so we can stay profitable.”
While the company relied on precision hand tools and four different Brown & Sharpe CMMs, Drozdowski had his eye on the potential of vision equipment for the past few years. He believed that certain aspects of almost every job Accu-Tech Inc. does could be improved if vision inspection were integrated into the measurement mix. Under certain conditions, vision equipment can collect data faster, provide greater accuracy, reach into small areas inaccessible to tactile probes and totally eliminate the distortion that inevitably results when tactile probes contact soft surfaces.
As promising as these advantages appeared to be, two problems discouraged Drozdowski from pursuing his idea. First, conventional vision systems are typically restricted to 2-D or 2.5-D measurement, but the bulk of Accu-Tech’s work is 3-D. Second, vision measurement systems required esoteric programming skills totally unlike the intuitive CAD-based programming his staff was used to with CMMs.
“To be of any use to me, a vision system needs to be programmed and operated like a CMM,” Drozdowski says.
Getting His WishWhen Wilcox Associates Inc. (Elgin, IL, a Hexagon Metrology Co.) approached Drozdowski about becoming a beta site for a new, vision measurement software product based on the popular PC-DMIS CMM program, which controls all of Accu-Tech Inc.’s CMMs, he jumped at the opportunity. PC-DMIS Vision, part of Wilcox Associates EMS suite of metrology software products, gives operators sophisticated tools for vision metrology and allows them to combine both tactile and vision measurement on a single machine. The software shares its interface, its underlying computer code and its database with the industry standard PC-DMIS software for Camps. PC-DMIS Vision is standard on new TESA manual and DCC Vision machines, available on new Mycrona vision systems, and can be retrofitted to older vision equipment, including products from OGP and Ram Optical.
To move forward with the beta project, Drozdowski obtained a Mycrona Altera vision system equipped with PC-DMIS Vision. This system can use tactile probes, vision and white light sensing as needed within a single program. He then spent the first nine months of 2006 working closely with Wilcox vision experts to fine-tune the software, as well as to recommend and test improvements that resulted in his multi-sensor vision system performing more and more like a CMM. “They have done exactly what I had hoped for. The only difference between the vision and CMM software is that you have a new sensor-a video sensor. So you can imagine how comfortable people will feel in just a short period of time,” Drozdowski says.
Like CMM software, PC-DMIS Vision uses an imported CAD model of the part as the basis for creating measurement routines and generating reports based on the captured data. In addition, programmers develop and test their programs either on or off-line by pointing and clicking on a CAD model of the part. They edit programs using simple cut and paste techniques. They can edit programs in any order-all things that vision measurement programs previously have not been able to offer. These, along with other features of the new software, can reduce measurement-programming labor by as much as 75%.
MainstreamingDuring the evaluation period, Drozdowski adapted existing PC-DMIS CMM programs to incorporate his multi-sensor machine into the main stream of his existing workflow. “This was a very safe bet,” he says, “because if I couldn’t get it to do what I wanted with the vision sensor, I could always use it like a CMM and keep work moving.” This was rarely a problem, though.
The 3-D capabilities of PC-DMIS Vision were very important because almost all of the work Accu-Tech Inc. does involves 3-D surfaces. The vision system does not need to find an edge to precisely locate a measurement point. It can take a surface point with submicron accuracy using precision focus algorithms.
While programming the multi-sensor system for a 3-D part, Drozdowski selects either the tactile or the vision probe interchangeably to deliver an optimum combination of throughput and accuracy. He obtains the best of both vision and tactile measurement but only has to create one program and perform one setup prior to measurement. “This allows me to improve both productivity and accuracy on every job I do on the multi-sensor system,” he says.
Going All OutIn October, after confirming the reliability of the product, Drozdowski equipped his machine with the latest high-speed controller. Within the month, it was one of the most active pieces of measurement equipment in the shop and he was aggressively pursuing a wide range of projects suited to PC-DMIS Vision.
Early WinsOne of the first measurement jobs that demonstrated the advantage of integrating tactile and vision measurement was evaluating the dimensional integrity of doors used to govern the flow of air in an automotive air-conditioning system.
In the past, Accu-Tech Inc. had the opportunity to do this work, but refused to take it on because of concerns of measurement accuracy caused by part deflection. Measuring 80% of the door itself with tactile probes was not a problem. The difficulty was that geometric measurements of the soft multi-material seals around the perimeter of the door were unreliable because the tactile probe distorted them. Any layout facility that had done tactile measurements on parts of this nature in the past had made unacceptable measurement errors. However, using vision to measure the 3-D seal geometry provided consistent data and showed that the customer’s manufacturing processes were stable and producing good parts.
Drozdowski learned that it was easy to measure small things such as electrical connectors without being limited by the diameter of a probe tip. Even better, he could measure the geometry of specialized nozzles with his hard probe and the position of minute nozzle orifices, less than 0.002 inch each, simply by using the CAD model to zoom in the vision sensor, turn up the magnification and collect data from this critical area of the part. Drozdowski could not even see these features with the naked eye.
Sometimes Drozdowski just needs to take one or two fast vision measurements. He can use it just like he would a CMM-swing the vision head over the part, focus and capture the desired measurement points. PC-DMIS vision can even be used as an optical comparator with its flexible series of software tools.
Accu-Tech Inc. has been approached to develop programs for parts to be measured on a series of Mycrona machines in a 24/7 production manufacturing environment. The customer has nearly a dozen Brown & Sharpe machines with PC-DMIS software. “The beauty of all this,” says Drozdowski, “is that their operators are going to jump from the tactile mode to vision. Because of their familiarity with the CMM software, they will soon be running vision with just a little training.”
Undoubtedly, there are some important differences between tactile and vision measurement. Operators coming from the tactile world will have to learn how lighting, focus and magnification interact to affect performance. Those coming from the vision side will have to learn how to set variables such as approach vectors to ensure tactile measurement precision. Fortunately, these critical parameters can be set and adjusted semi-automatically within the common software.
“If you are a current tactile probe operator who is just going to run, and not write programs, you can be off and running after an hour of training. There is so little to think about, it’s not even funny,” Drozdowski notes. “You won’t even know that you are in the video world. The look and feel is the same for both types of measurement. You just have to know how to run an existing program, and how alignments work. Of course, if you want to become a fully proficient vision system programmer, that will take you longer. After using PC-DMIS Vision for six months, there is very little that can stump me.”
Today Accu-Tech’s multi-sensor vision system is 100% used and most of these projects use both tactile and vision sensing. Drozdowski has begun talking openly with nearby aerospace, automotive and medical device manufacturing firms about his advanced 3-D measurement capabilities.
Drozdowski has hired a proficient PC-DMIS CMM programmer and will train him on how to use PC-DMIS Vision. Because of his beta site experience, he expects to teach the new person the requisite skills for multi-sensor programming in a fraction of the time it took him to learn.