Quality Innovations: Structural Lighting Broadens the View
When it comes to measurement, one trend is clear: Manufacturers are embracing technologies that boost accuracy, speed and, ultimately, productivity both in their inspection and reverse engineering processes. From piston heads to stamping parts to car clay models, a white-light, noncontact 3-D digital measurement machine newly introduced to North America promises to meet manufacturing objectives in a way conventional coordinate measuring machines (CMMs) to date have not.
The Surftizer Series 3-D measurement machine by Opton (Seto, Japan), parent company of MiiC America Inc. (Canton, MI), performs the same functions as conventional CMMs except for one key difference. "The Opton technology uses a white light optical sensor to digitize a curved surface into X, Y and Z points," explains Tobby Li, 3-D systems director for MiiC America. "For example, a 4- by 6-inch area, or ‘patch,' can be digitized into a set of points in just a few seconds. The total number of points measured in one patch can be up to 100,000 per second compared to a CMM's capacity to measure about one point per second."
Opton's white-light structural lighting method uses a grating pattern-
parallel black and white lines-that is projected onto a 3-D surface via a light source and projection lens. Detailed features on a curved surface such as marked lines, ink lines, fillet R-edges and edge lines, can be extracted. Information about the 3-D shape is encoded into the deformed grating image, and a digital camera allows for computer imaging. Using the Fourier Transform method to decode the shape information from the deformed grating image, the technology digitizes the surface into a set of points with known X, Y and Z coordinates.
This allows for a whole-field view of measurement that digitizes an area from 1 by 1 inch to 20 by 20 inches at a time. Because of its fast measurement speed, the technology can measure up to 1.2 million points in less than 10 seconds. Not least, according to Li, the technology's capacity for high-data density allows for spacing of measured points to achieve an accuracy of about 0.05 millimeter.
The Surftizer machine performs the same job as a conventional CMM. "This technology distinguishes itself through the use of automation," Li says. "Several automation goals can
be achieved using our technology. It requires less labor-or attended
measurement-and it allows for programming features. For example, an operator needs only to load an object on a turntable, choose a pre-set inspection program to run and then push the start button. Once the measurement is completed, the data can be compared with CAD or master data.
"The data comparison is conducted in less than five mouse clicks, and a color-coded 3-D map shows up on the screen," Li adds. The operator needs only to pay attention to certain colors to make any needed annotations. Also, there is no need to merge different views and overall accuracy is guaranteed.
Manually measuring an object that requires multiple measurements using a noncontact 3-D sensor is labor- and skill-intensive. This results in a longer measuring time and uncertainty in data quality. Like CMMs, Surftizer machines use joysticks to move and rotate the sensor and object while conducting multiple measurements, which dramatically reduces measuring time. For parts that need to be inspected several times a day, the technology can be programmed to conduct unattended measurements.
Another advantage is the technology's use of one coordinate system. Regardless of where the sensor is positioned or whether an operator is measuring from different viewing angles, the measurement results are placed in the same coordinate system. This means there is no need to merge various views from different coordinate systems into a single data set. The result is a savings in merging time. "This eliminates merging error, which varies from object to object and from operator to operator," Li says. "As a result, a Surftizer machine typically can be used by 10 to 20 operators daily. Most of the time, the machine is running unattended measurements."
When it comes to white-light, noncontact 3-D measurement, the technology uniquely provides for fully automatic inspection from measurement to data processing to reporting, he adds. The Surftizer Series provides for measurement of small objects such as piston heads and golf clubs. The mid-size machine can measure everything from engine blocks to stamping parts, and it can be used to integrate a conventional touch probe into the machine to allow for both contact and noncontact measurement. A large machine can be used for measuring scaled-down car clay models and stamping assemblies. The largest machine often is used for full-size car measurement.
A variety of applications
The Opton noncontact technology originated in Japan but has been used in a variety of North American applications during the past couple of years. In one application, a manufacturer started using the Surftizer 700S technology in early 2004. The plant provides engines for all of its manufacturing operations in North America. Having produced 1.2 million engine products in 2004 alone, the plant has been focusing on ways to avoid delays in finding engine block problems and reduce the number of blocks being scrapped.
"A touch-type CMM probe had been used to inspect the engine blocks after casting but, because a CMM can measure only a few hundred points on an engine block in about 40 minutes, areas that the CMM cannot measure can cause problems," Li says. "To inspect as much area as possible on an engine block in the same amount of time, the plant installed the Surftizer 700S to inspect points every 0.8 millimeter, which leaves no room for error.
"The whole measurement takes the same amount of time as a CMM except that now we have achieved a measurement of 4 million points," he says. "Plus, the error is color-coded and easy to understand."
In addition to automotive applications, the technology has been used to inspect everything from aircraft turbine blades to electronic devices to printer parts. "The key benefit is more control on product quality," Li says. "Because the technology can provide 100% measurement, users in a short time can reduce their scrap ratio. That represents a significant savings."
• The 3-D measurement technology by Opton performs the same functions as conventional CMMs except that it uses a white light optical sensor to digitize a curved surface into X, Y and Z points.
• The white-light structural lighting method uses a grating pattern that is projected onto a 3-D surface via a light source and projection lens. The 3-D surface shape information is encoded into a deformed grating image and a digital camera allows for computer imaging.
• Because of its fast measurement speed, the technology can measure up to 1.2 million points in less than 10 seconds. Its capacity for high-data density allows for spacing as small as 0.05 millimeter.