Laser Radar (LR) is a laser based measuring technology that is gaining ever increasing focus from automotive and aerospace OEMs due to its speed and ability to bring automated absolute CMM quality measurements to the production line.
The Nikon Metrology Laser Radar solution provides automated, non-contact measurement capability for medium to large-volume applications of up to 50 meter radius. This next generation of metrology system precisely measures geometry without requiring photogrammetry targets, laser tracker spherically mounted retro-reflectors or probes. The LR measuring device is suited for complex, repetitive, hard-to-reach, delicate and labor-intensive inspection tasks in automotive, aerospace, renewable energy, high-end manufacturing and other industries with medium to large scale measurement applications.
Laser Radar implements a Spherical Measurement System returning Range, Azimuth and Elevation which is converted to cartesian coordinates relative to the Laser Radar. LR also returns the quality of each measurement which is important for data filtering. LR is unique in that it measures range using Frequency Swept Interfererometry (FSI), also known as Heterodyne Interferometry, which combined with Beam Focusing allows LR to operate without targets to a high accuracy..
LR offers repeatable fully automated measurements, its contact free measurement method also allows inspection of uncured carbon fiber and other delicate surfaces without risk of damage or distortion. The LR is not sensitive to lighting or temperature and can measure most surfaces including glass and can also measure through transparent materials.
LR accuracy is dependent on the measurement distance and accuracies range from 24µm at a 2m distance to 300µm at a 30m distance. Nikon Metrology’s LR propriety laser technology offers inspection speed up to 2000 points per second in ultra-fast Vision Scan capture mode.
LR inspection plans can be generated completely off-line using CAD with seamless integration with manufacturing processes which can include in-process inspection using LR mounted on industrial robots.
A fully automated in-line or near-line LR inspection system comprises the LR mounted on a standard 6-axis Industrial Robot. The robot automatically positions the LR allowing inspection of areas otherwise hidden from line of sight. The Laser Radar automatically measures alignment points after every robot move, guaranteeing all measurements are collected in a common coordinate system and ensures the measurement accuracy is completely independent of the robot.
These type of systems create a true shop floor CMM but measuring up to 6 times faster than a traditional CMM. In a recent application, an automotive body-shop implemented LR into its production facility and is obtaining CMM quality measurement data on 40 vehicle bodies/day with 1000 features/body being measured. Something never before possible with traditional measurement technology.
Transitioning to any new measuring technology is always difficult and requires a direct analysis of past measurement methods (CMMs, Laser Trackers etc) with LR non-contact laser technology.
System Accuracy and Correlation Errors
Nikon Metrology has developed a correlation process to assist customers to compare CMM measurements to Laser Radar.
Both LR and CMM accuracy and traceability are defined by ISO 10360; a specific version, 10360-10, was introduced in 2016 to cover both laser Trackers and Laser Radar based spherical measuring systems. To compare measuring systems Measurement Correlation Errors become important which represent the differences between reported position of measured features by each measuring system. Correlation Errors include measurement differences, alignment differences, part holding differences, and environmental differences.
The developed six step process strives to minimize differences including working in controlled conditions whenever possible.
Artifacts used for the test include both a Feature Artifact and an Accuracy Artifact. The Feature Artifacts is concurrently measured on a high accuracy Bridge CMM and the LR. In addition a User Artifact can also measured representing a typical customer part with all of the measured data analyzed and a Correlation Error report generated. In the selected Feature Artifact test the CMM measurement took 285 seconds for 15 features, while Laser Radar took just 41 seconds – 7 times faster. Correlation cab be achieved to within 50 microns.
A 1.5m Tetrahedron Accuracy Artifact is concurrently measured by a Horizontal Arm CMM and the LR. The artifact consisting of 4 spheres creating 6 distances with 7 micron uncertainty. The Laser Radar was positioned to measure all 4 spheres. Normally a CMM can only measure 3 spheres with a single probe orientation necessitating measurement of the artifact twice using two different alignment routines.
The accuracy data obtained from the test demonstrate Laser Radar can significantly outperform CMM accuracy data proving that Laser Radar is not only fast but also accurate and capable of performing automated absolute CMM quality measurements in the production line.
North American LR installations include BMW, Tesla and the FCA Mini-Van assembly plant in Windsor, Canada where the Laser Radar measuring cell allows the plant to measure 15 vehicles a day compared to just six with CMMs.
For more information: www.nikonmetrology.com