New Case Story: Laser Radar for automated inline inspection
May 16, 2014
Today’s inspection methods during automotive assemby
It is important for automotive assembly plants to continuously monitor process quality during the manufacturing process. Locations of holes, slots, studs, welding lines and other features need to be measured on the vehicles in Body in White (BI W) assembly. Also, flush & gap for door or hinge lines need in-depth verification in the Trim and Finish section. These inspections ensure that vehicles are built within the stringent tolerances set by automotive manufacturers.
These measurements in the past have been primarily performed by either horizontal arm CMMs offline or on the production line using dozens of sensors individually aimed at each of the features that are to be inspected.
Although CMMs provide highly accurate absolute measurements, they require an expensive metrology lab and can only be used offline. A large amount of time is required to remove the vehicle from the line, fixture and align it in the CMM and then perform the time-consuming measurements. At best, two vehicles can be inspected per shift on a CMM. This is a very small sample considering that over 1000 vehicles can be built each day in a single automotive plant.
Traditional inline systems can have over 100 fixed sensors that are all individually aimed at features on the vehicles. These fixed sensors are demanding to install and maintain and do not provide ‘absolute measurements’ of the features in the car’s coordinate system. They can only detect presence/absence of the features in a local reference frame making it impossible to do a complete dimensional check on the vehicle.
In addition, most assembly lines now are ‘flexible’, meaning that they can produce more than one type of vehicle. Fixed sensors cannot be used between different vehicles styles, every vehicle requires it’s own custom set of sensors.
Nikon Metrology’s Laser Radar
The Laser Radar provides a unique alternative to the shortcomings of the traditional inspection methods. The Laser Radar performs automated, highly accurate, contactless measurements by using a focused laser that is controlled by precision azimuth and elevation drives. To perform a measurement, the Laser Radar only needs a fraction of the laser’s signal to be returned giving it the ability to measure almost any surface, including highly reflective bare body panels as well as shiny painted surfaces and even lights, which are very difficult to measure with typical line scanners. This robust measurement ability means that the Laser Radar can be used for both BI W and Flush and Gap inspections on finished cars.
The Laser Radar also has a large measurement range (up to 50m for the MV350), allowing it to easily measure objects that have the size of cars, trucks, and other large vehicles.
Inline inspection with the Laser Radar
For the inline inspection, Laser Radars are mounted to 6-axis robot arms that are located on each side of the production line. This type of robot is common place in automotive production facilities, is very robust and can easily handle the payload of the Laser Radar.
The robots are used to automatically reposition the Laser Radar so it can inspect areas that are hidden from the line of sight of a single Laser Radar location. For example the door frame or other body panels could be blocking the line-of-sight to some features on the floor pan; repositioning the Laser Radar to an alternate location will make these features visible one again without the need for multiple sensors.
After the robot repositions the Laser Radar, it automatically measures alignment points on the vehicle or pallet. This occurs each time the robot moves the Laser Radar, guaranteeing that all measurements are collected in vehicle coordinates and ensuring measurement accuracy is independent of the robots ability to position the Laser Radar.
In each location the Laser Radar can measure dozens of features on the vehicle. These measurements are preprogrammed in the inspection software directly from the vehicle’s CAD model. After the initial programming, data collection and reporting is fully automated.
Unique inspection scripts can also be written for each vehicle style and model made on the production line making the Laser Radar inspection station completely flexible. Adding vehicle styles in the future only requires re-programming of the inspection plan and does not require any physical changes or new hardware.
The interaction of the Laser Radar, robot, and analysis software are fully integrated; the inspections are completely automated and do not require manual intervention during runtime, improving both the speed and quality of the measurements over traditional methods.
Laser Radar features
The Laser Radar is a programmable contactless measurement system and has an accuracy <0.1mm over the volume of a car. It can be fully automated and can directly measure holes, studs, bolts, along with many other features accurately from a large standoff, eliminating the risk of ‘crashing’ into the vehicle.
The Laser Radar measures up to 2,000 points / second making it suitable to not only measure features but also scan surfaces. The ability to offline program the Laser Radar makes it ideal for inline inspections; different vehicle models on the same assembly line are simply a new inspection program.
The Laser Radar is proven in industry as a reliable precision measurement instrument and is used in aerospace, renewable energy, as well as automotive applications.
Scan speed: Up to 2000 pts/s
Range (Radius): MV330: 1 to 30 m/ MV350: 1 to 50 m
Field-of-View: Az: 360°/ EL:+/- 45°
3D accuracy: (2 μ)24 μm @ 2 m/ 102 μm @ 10 m/ 301 μm @ 30 m
Laser: Class II