3-D Measurement: Affordable Portables—One Manual, One Auto

During the last couple of decades we have seen huge advances in laser trackers, portable arms, structured light scanners, laser scanners, photogrammetry devices, and other 3-D measurement technologies that have made accurate 3-D shop floor measurement more feasible than ever before. Each of these technologies has its own set of tradeoffs—accuracy, measuring volume, portability, durability, or ease of use—but the clincher for many small machine shops has been the price.

There are few entry-level, low-cost, 3-D measurement devices suitable for the shop floor and for use in on-machine inspection in particular. This is critical because verifying the accuracy of parts while they are still fixtured in the CNC machine has long been recognized as a key way to reduce cost and improve both quality and throughput for machined parts. According to the 2002 U.S. Economic Census, small machine shops make up more than 85 percent of machine shops in the United States. This presents a huge marketing opportunity for 3-D inspection equipment manufacturers and if the devices were affordable enough, would offer a productivity tool that could greatly enhance the capabilities of small machine shops across the country.

In the past year, two entry-level 3-D measuring devices have been introduced: the manually operated Master3DGage from Verisurf—released in mid-2010, and the fully-automated direct computer controlled (DCC) zCAT from Prrrfect Technologies, due out this year. Both devices are positioned as affordable 3-D gauges for the shop floor. While both can be used for general-purpose gauging, the developers say on-machine inspection is definitely one of the target markets.

Why bother?

Before we delve into the specifics of these two products we need to address why there is a need for a separate tool for on-machine inspection when many of today’s CNCs are sold with, or can be retrofitted to do, on-machine verification (OMV) themselves.

Although several such solutions exist, they may not make sense for the small or low-volume shop. In order to get the accuracy and overall functionality that you would get with a separate measuring device, you have to invest in the CNC hardware that will do the inspection, specialized software (since CNCs are not by nature 3-D measuring devices), and perhaps some specialized training.

Delcam, a leading supplier of advanced computer-aided design (CAD) and computer-aided manufacturing (CAM) solutions for manufacturing, will retrofit an existing CNC for on-machine verification for about $20,000. This includes probes (such as the Renishaw MP700 or OMP400 probes), hardware accessories (e.g., wireless transmission and mounting), installation, and Delcam’s PowerINSPECT software.

However, that is per CNC, a not-inconsequential point. What you end up with is a dedicated, fully-automated, on-machine verification system, which makes sense for high-volume shops or those that make larger parts, but may not make sense for smaller or low-volume shops. One advantage among many for a separate 3-D measuring system as opposed to an in-built system is that it can be moved from one machine to the next, or can be used for shop-floor gauging or some other measurement function when not being used on the CNC. Again, this is a more cost-effective solution for the low-volume or small-shop owner.

Because Delcam sells inspection software for both dedicated OMV as well as portable 3-D measuring systems, the company can speak knowledgeably about the pros and cons of each. “OMV is a more automated solution,” explains Philip Hewitt, product manager for Delcam Global PowerINSPECT. “It is less versatile and takes a little bit more setting up—the probing is tied to a particular machine. The programming is a bit more involved because it must handle all of the machine movements and avoid collisions. Typically it will take more time and effort for the ‘one off’ case. But it is much better for repeated operations—the automated measurement is faster and more consistent. It is also more suited to larger parts, even for one-offs.”

In theory, OMV can be very accurate, up to around 2 microns, says Hewitt. However, the accuracy of the system depends on the machine tool itself, and this can be more difficult to assess. “It is important to benchmark the machine at the beginning to understand the accuracy, and to monitor this over time,” Hewitt explains. “One of the key issues is that machine tools generate a lot of heat when they are cutting, and this affects the accuracy until the machine cools down. It is important to keep a constant check on the accuracy, periodically and before any critical measurement.”

An advantage with portable 3-D measuring devices, such as those we will look at here, is that they are independent of the machine tool. “So although the accuracy is typically not as good, you avoid the question mark of the machine ‘measuring its own work,’” Hewitt points out.

The zCAT

Coming to the market soon is a new device from the same person who developed the Romer Arm, Homer Eaton. Portable arms, such as those from Romer, Faro, and others, revolutionized manufacturing inspection by allowing 3-D inspection to be done on the production floor. But as useful as arms are, they are manual devices. If unattended operation with improved accuracy is required, a DCC device is the direction you need to go.

Eaton’s company, Prrrfect Technologies, is about to release the zCAT, a small, cylindrically shaped device measuring roughly 24 in. tall by 18 in. wide (including the horizontal arm). The DCC, 27 lb 3-D measurement instrument can be brought anywhere on the shop floor, including inside a CNC machine for automated on-machine inspection.

Hank Kraus, president and CEO for Prrrfect, says the company is positioning the zCAT as the “world’s first truly portable DCC CMM.” From the start the zCAT was developed for the shop floor so that it could be easily moved between shop work centers and even operated inside a machine tool.

It turns out that the latter was a bit of fortuitous thinking on Prrrfect’s part. “We had considered the application inside a machine tool early in the design process,” says Kraus. “But we underestimated what we now believe is significant market demand. It also happens to be priced competitively with entry-level CMMs so we think it will be successful in that market as well. As far as we know, there is nothing out there that compares.”

Figure 1: Prrrfect’s zCAT

As with a CNC-based OMV system, the zCAT is intended for a production-oriented environment with automated measurements. In this sense, Kraus is positioning the zCAT as an alternative to dedicated OMV. But Kraus thinks the zCAT’s accuracy may attract more than just production-oriented customers. “With this device we think we will see a big shift from lab measurement to shop-floor measurement,” says Kraus. “Because of its accuracy and because it can be used manually, it may make more sense to have an operator, or even an inspector, take sample measurements on the shop floor rather than pulling a part off the line and taking it back to the lab.”

The zCAT’s unique design incorporates two linear axes as well as rotation: the column moves up and down, the arm moves back and forth, and the entire column rotates. Therefore, column linear movement gives you the Z axis, and the arm linear movement combined with the columnar rotational movement provides the X and the Y motion. Kraus says the current version of the product has a volumetric accuracy of 8 µm. The horizontal arm will hold a probe on either end, as shown in figure 1, in this case, a touch probe on one end and a line scan probe on the other. The zCAT has a maximum reach of 12 in., a total measurement height of 12 in., and a measurement volume of about 1 cubic ft. The volume does limit the zCAT to the measurement of smaller parts.

Eaton designed the zCat from the bottom up to be accurate, lightweight, power-efficient, shop-hardened, and inexpensive, says Kraus. “The single simplified controller board is incredibly cost competitive because it uses custom programmed firmware with inexpensive off-the-shelf components for encoder interpolation, motion control, I++ interface, and ControlCAT geometric measurement software,” he says.

The zCAT is battery operated with an expected battery life of about five hours.

The lightweight design means it can be used on existing surface plates with no additional mounting requirements or safety issues. Kraus claims the zCat is the first CMM to have the I++ interface built into the device. The onboard wireless I++ server means it can be controlled by any computer on the network using any I++-compatible metrology software (e.g., Rational DMIS, Open DMIS, CMM Manager PCDMIS, and others).

It is possible to toggle the zCat between manual and DCC mode, providing the user with an arm-like experience for easy referencing and quick manual measurements. Besides size and price, one advantage the zCAT has over an arm is better accuracy, says Kraus. “Often an arm is used for repeat measurement, where the same type of part is measured over and over,” says Kraus. “The zCat is more accurate for these types of repeat measurement because it isn’t susceptible to operator influences. It also provides a more cost-effective platform, reducing the production touch time for measuring parts.”

The zCat is expected to roll out at about $25,000, including the embedded ControlCAT metrology software. For part-to-CAD inspection or for special reporting requirements, any I++ metrology software will perform out of the box. Shipments are scheduled to begin this summer, some time after the CONTROL International Trade Fair scheduled for May 3–6 in Stuttgart, Germany.

Master3DGage

If Prrrfect Technologies hopes to take on the arm market for OMV use, they are going to go up against the Master3DGage from Verisurf (figure 2). Yes, it’s a portable arm, so it doesn’t have the advantages you get from a DCC device, but it has at least a one-year head start on the shop-floor and OMV market and the oomph of Mastercam behind it (more on that later).

The Master3DGage is actually a rebranded ROMER Multi-Gage. So there is some shared DNA between the Master3DGage and the zCAT. From what we understand, the ROMER Multi-Gage was an underpromoted Hexagon product probably languishing in the shadow of the new ROMER Absolute arms, but it was perfect for what Verisurf had in mind—an affordable and portable rapid 3-D inspection solution that would let machine shops increase production and improve part quality.

We had a chance to use the Master3DGage at last year’s IMTS, and the first thing that strikes you is how well-balanced and easy to use it is. Part of this is the size, of course; it’s a small arm. But the other part is that the arm’s weight is offset by a counterweight rather than internal springs, which gives it a much lighter feel and transfers all the weight of the arm straight down the base.

Delcam’s Hewitt notes that manual portable-inspection solutions such as Faro or Romer arms are suitable for small parts, but obviously limited by the size of the measuring device. “[A manual portable] is the most versatile solution for one-offs,” he says. “The inspection ‘programming’ is the simplest because it doesn’t have to deal with the machine motion; it is carried out manually by the user.”

In the case of the Master3DGage, the measuring volume is about 4 ft, and the included Verisurf software simplifies even complex inspection measurements. The unit has a respectable volumetric accuracy of 18 µm, making it more than adequate for many on-machine inspection needs.

“At 28 pounds it is light enough to move around a machine shop and place inside a machining center, yet heavy enough for stability while measuring,” notes David Olson, Verisurf’s director of sales and marketing. “The size and shape, base handles, and counterbalance design of the arm also add to its portability as well as its stability while measuring.”

As with the zCAT, one goal for Verisurf is to make inroads into the OMV market. Because the Master3DGage is so well balanced, it can be set on any stable flat surface, like inside a CNC, and used for measuring parts while they are still fixtured. Couple that portability with the fact that the Master3DGage comes with a single license for Verisurf’s 3-D CAD-based software, and you have a tool that is ready to measure right out of the box.

In what amounts to a real coup by Verisurf, the Master3DGage is sold exclusively by Mastercam resellers around the world. “So, for existing or new Mastercam users, there is now a seamless path that takes them from design, to machining, to inspection, all in the Mastercam environment,” says Olson. And because the Master3DGage comes with Verisurf software, the user is exposed to Verisurf’s advanced, 3-D model-based inspection with integrated geometric dimensioning and tolerancing (GD&T) inspection capabilities. This complete solution delivers a precise, fully automated digital process to inspect directly to CAD models anywhere on the shop floor, says Olson.

The Master3DGage can be used for general-purpose shop-floor gauging as well. Its 4 ft measuring volume is probably enough for most measurement needs, but Verisurf also sells the GagePlate system, which automates realignment of the Master3DGage around large parts under inspection while referencing one coordinate system. The precision-calibrated plate rapidly scales and aligns the Master3DGage, enabling the inspection of large parts without the accumulative errors associated with leapfrogging or the higher cost and lower accuracies associated with longer arms.

The Master3DGage plus software runs about $33,000. The Verisurf software bundle by itself is worth about $15,000.

 
Figure 2: The Master3DGage from Verisurf

Conclusion

There are some tradeoffs with any technology you choose. Here the question really is, “Do you need an automated measuring system like the zCAT, or will the Master3DGage portable arm work for you?

In terms of cost, both units might run you about the same price. The zCAT by itself is less expensive, but if you need advanced measuring software, you will need to pop for that to run the zCAT. The zCAT has better volumetric accuracy but a smaller measurement volume. If you are already in the Mastercam environment, that may also have a bearing on your decision.

Either way, both Prrrfect Technologies and Verisurf are opening up opportunities for small machine-shop owners who have longed for tools that enhance their quality and productivity by putting them on even footing with bigger shops. In today’s manufacturing environment, with small shops feeling the pinch from overseas vendors, any tool that helps them compete and keep U.S. manufacturing strong are worth a good look.

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