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.