The multisensor advantage
- February 3, 2012
by Tim Wilson
Tactile coordinate measuring machines (CMMs) and vision based non-contact systems each have their advantages. But combining the two in a single system can provide more measurement data more quickly to improve process control feedback, as well as saving time and cost, compared to measuring parts on several different systems.
“Our technology has evolved to incorporate a sophisticated array of sensors,” says Jaime Murray, senior applications engineer at Optical Gaging Products (OGP), a division of Quality Vision International (QVI), Rochester, NY. “We have a large product line that incorporates tactile probes, lasers, optics, micro-probes, and the 3D measurement analysis software needed to run it all.”
The ability to deploy sensors in a three dimensional multisensor environment means more measurements can be taken, quickly and accurately. It also means multisensor CMMs need sophisticated software to interpret the wide range of data coming off of the sensors. And because these sensors are being used interchangeably, with their positions changing depending on the application, getting the analysis right is crucial.
“OGP’s systems are equipped with either the standard measuring software–Measure-X–which is 2-1/2 D measuring software, or MeasureMind 3D, which is 3-dimensional metrology software,” says Nate Rose, applications engineering manager at OGP. “Both programs excel at gathering data points from an array of sensors.”
These software applications provide the feature size, geometry and location measurements required by manufacturers. They also support industry quality control requirements that touch every point in the supply chain.
Multisensors for many touch points
“The trend is toward systems that are versatile and that can address a variety of needs,” says Mark Arenal, general manager at Starrett Kinemetric Engineering in Orange County, CA. “We need to meet a cross section of different applications that our customers have; the technology has to be easy to use, and must have interfaces that are comfortable and intuitive, much like a home computer.”
Starrett Kinemetric builds complete video-based and multisensor measurement and inspection systems. Some are fully equipped with optics, cameras, touch probes, and lasers.
“It’s amazing what can be done today with digital video,” says Arenal. “We used to have to use a frame grabber in the PC, but these days the camera does that by capturing images.”
But, given all of these capabilities, is a multisensor too much technology for a smaller metalworking shop, and is the cost prohibitive? The answer is a qualified “no” to both.
“The barrier to entry in this field has certainly gone down,” says Arenal. “There are a wide range of products and solutions out there, but for high accuracy you need the technology to be on a precision platform. You just can’t fake that. You can gather data all day long, but if the data captured is not accurate you are just recording bad data.”
Arenal emphasizes that the calibration has to be solid, well-documented, and properly supported by the manufacturer. Systems need robust software and, often, have to reflect the requirements of original equipment manufacturers further up the supply chain. That means that, even for smaller shops, it can be advantageous to go with multi-sensor measurement equipment.
“The new software can do amazing things, with better measurement and data acquisition, higher resolution, and better report generation,” he says. “That’s important, because many job shops are subcontracting to companies that need a complete quality inspection report.”
Software, in fact, is a big reason why many CMM users upgrade. Having an application that runs slowly, or is non-intuitive, can be frustrating and reduce productivity. And when upgrading to a trigger probe or a three axis scanning sensor, the right software will result in automation improvements that can bring real cost savings.
“The majority of our software development group resides in Germany where they produce Calypso, our flagship, CAD-based, visual metrology software that accompanies Zeiss CMMs” says Mike Roterdam, technical sales engineer at Carl Zeiss Industrial Metrology, LLC, Maple Grove, MN. “We also staff in-house developers here in the United States.”
Zeiss CMMs include the F25 MicroSystem with a length measuring error, MPE_E(µm)= 0.25 + L/667. It can measure microparts with low-force tactile probing or non-contact optical sensing. The MICURA also has “sub-micron” accuracy at MPE_E(µm)= 0.9 + L/400. It carries the VAST/XT-Gold active, high performance scanning probe and supports a smaller overall footprint with a measuring volume of 500 mm3 (20 in3).
As well, the O-Inspect multi-sensor optical and contact measuring system comes equipped with standard VAST/XXT passive scanning probe and a Discovery V12 telecentric zoom lens. Zeiss recently introduced an optional white light distance sensor to inspect a wide variety of reflective, transparent and matted 3D topographies.
“Other machines of ours support the RDS (rotary dynamic sensor) carrier. You can attach to it several different types of sensors, including the Vast/XXT passive scanning probe, ViScan optical sensor and the Laser LineScan. The RDS rotates in 2 additional axes 360 degrees at 2.5 degree increments,” says Roterdam. “This delivers over 20,000 different angles for the sensors.”
Zeiss also has the ability to work within large–and demanding–application environments.
“We have CMMs as big as a room where you could park a car or a jet fighter under it,” says Roterdam. “If it has MASS (Multi-Application Sensor System) technology, you enjoy the benefits of Vast active scanning combined with the benefits of the RDS and its assortment of supported sensors.”
The camera has to fit the system
For a camera to be effective, it has to match to the optical system.
“It’s important to note that the optical system must be designed to provide an image resolution that is matched to the camera's resolution,” says Murray from OGP. “It is not useful to put a multi-mega pixel camera on a low res optical system.”
While OGP offers cameras with resolution up to five megapixels, it only offers very high resolution cameras with appropriate high resolution optics. “We match the optical and camera resolutions, as well as any other sensors, to the feature sizes and tolerances of the parts being measured.”
As well, OGP facilitates data sharing via its SmartProfile software, developed by Kotem, QVI’s analytical software division.
“SmartProfile works with data from any measuring system – not just OGP systems–so it is possible for data from various kinds of equipment to be compared on an ‘apples to apples’ basis,” says Murray. “SmartProfile operates according to the ASME and ISO international standards for geometric dimensioning and tolerancing; in a global supply chain environment, this capability is vital.”
OGP also has its SmartLink I++ interface package. SmartLink enables measuring systems which have I++ compatible interfaces to communicate and exchange programming steps.
“For example, an operator skilled in Zeiss Calypso software could use Calypso and SmartLink to set up a measurement program for an OGP SmartScope,” says Murray.
For tough jobs – go linear
For metalworking applications, specialized linear sensors can offer unique value, in large part because of their flexibility, and their ability to give real-time data in tough environments.
“We exclusively specialize in linear sensors that can be used in a variety of industrial machinery,” says Matt Hankinson, technical marketing manager for the Sensors Division of MTS Systems in Cary, NC. “Our sensors are designed into the machinery to provide continuous position feedback.”
MTS sells magnetostriction sensors, which are linear-position devices that pick up a sonic strain pulse induced by the interaction of two magnetic fields: one field comes from a movable permanent magnet, and the other from a current pulse along the waveguide.
“There is a wide spectrum of sensors at the high end–such as optical encoders–and then technologies like potentiometers on the low end,” says Hankinson. “Each have their strengths and weaknesses. We are in the middle ground, but our technology is robust–it can handle shock and vibration that might cause other sensor technology to fail.”
For MTS, approximately half of their magnetostriction sensors are sold to the machine builders, and the other half to owners of existing equipment who want to upgrade their machines, or who are looking for replacement parts.
“With a minimal investment you can improve productivity and reduce energy consumption, while increasing reliability and safety,” says Hankinson. “The technology also reports an absolute position; if you lose power you don’t have to move back to a reference point.”
In these scenarios, speed is important, too. MTS’s magnetostriction sensors can report to 10,000 times a second; and the resolution can get down to a single micron.