Quality Innovations: Laser Scan in 3-D

By Mark Robins

Scanning system takes 3-D laser scanning into fields not possible in the past.

NVision (Wixom, MI) has introduced a mobile laser scanner that is light and portable, yet can create a noncontact, 3-D scan of an object as accurately as a coordinate measuring machine (CMM). The new high-definition version of MobileScan 3-D laser scanning system moves the capability of 3-D laser scanning to fields not accurate enough in the past. The new high definition (HD) scanner provides high resolution with a point spacing of 0.001 inch and an accuracy of ±0.0005 inch while collecting measurements at a rate of 30,000 points per second.

Portable laser scanners are typically arm-mounted or completely stationary. They are capable of collecting many thousands of points per second but lose accuracy either through the seven axes of movement in the arm or the process of building a 3-D picture from separate "shots" from a stationary camera. The system is programmed to use only one of its three axes of movement at any time in a controlled manner. This way it can collect 3-D data in a single scanning session with CMM levels of accuracy. All measurements are automatically transformed into a common coordinate system in Geomagic software, meaning that there are no patches of data to be sewn together after scanning has taken place.

The new high definition (HD) scanner provides high resolution with a point spacing of 0.001 inch and an accuracy of ±0.0005 inch while collecting measurements at a rate of 30,000 points per second. Source: NVision Inc.

Higher Accuracy Inspection

"The HD version of the MobileScan 3-D provides a higher accuracy inspection and reverse engineering system than has been available in the past," says Steve Kersen, president of NVision. "Customers no longer need to choose between the speed of a scanner and the accuracy of a CMM. This opens up the opportunity to scan items that require a high degree of accuracy, such as turbine blades, in a much more comprehensive way and much faster than has been possible in the past with touch-probe technology."

Generally, the new laser scanner should be used on components shorter than 12 inches such as turbine blades that require measurement accuracy better than 0.001 inch, particularly where there is a benefit from automation. This means that precision-machined parts might make suitable applications. If larger sheet metal, clay or foam components need to be scanned, particularly on a one-off basis, an arm-based scanner is a better choice. The typical accuracy of the best arm-based scanners, 0.001 to 0.002 inch, makes them ideal for applications such as automotive styling.

The scanner's HD sensor has a two-axis servo-controlled swivel head that is integrated with a turntable. Movement of these three axes is programmable, allowing automation of measurement strategies. The key to the system's accuracy is that it uses only one servo and rotary encoder at any one time and these components are manufactured to the highest specification available. "By minimizing the opportunities for error to be introduced, the highest level of accuracy can be achieved," says Giles Gaskell, director of business development for NVision.

Manual or Automatic Use

The sensor can be moved manually or automatically controlled to follow a predefined measurement strategy. This means that the scanner can be left alone to scan production items without the constant attention required by a handheld device. The sensor projects laser light onto the surface of the object being measured, while a camera continuously triangulates the changing distance and profile of the laser capturing points at a rate of 30,000 per second. The density of the resulting point cloud is what enables the object to be accurately replicated.

Before scanning and during the measurement process, the new laser scanner continually senses the object's surface and ambient light conditions and automatically adjusts the sensor to obtain the best possible measurements. True 3-D data is collected in a single data set in Geomagic software because the scanner moves around the object it scans.

The scanner is easy-to-use, requiring only basic computer skills and the ability to use spreadsheet-type software in order to program scanning strategies. Operators only need to change the part and set the system running again, making the system useful in production environments.

The system connects easily to a standard notebook computer via USB or Firewire. The new scanner comes integrated with Geomagic computer-aided inspection software that automatically processes scan data from a physical part to generate highly accurate polygon and parametric surface models. This software also provides easy-to-understand graphical comparisons between computer-aided design models and as-built parts.

QUALITY SPECS

-The system is programmed to use only one of its three axes of movement at any time in a controlled manner.

-The new laser scanner should be used on components shorter than 12 inches such as turbine blades that require measurement accuracy better than 0.001 inch.

-The sensor can be moved manually or automatically controlled to follow a predefined measurement strategy.