Innovating Shopfloor Inspection: A Look At The Next Generation CMM

A rapidly changing technological landscape necessitates a leap in the quality of the current crop of Coordinate Measuring Machines (CMM) both in accuracy and the level of automation. Contributed by Nikon. 

In today’s inspection methods during automotive assembly, 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 (BIW) assembly. Flush and gap of doors and other hangers also need to be monitored and verified. These inspections ensure that vehicles are built within the stringent tolerances set by automotive manufacturers.

These measurements in the past have been primarily performed offline by either horizontal arm CMMs 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 tend to be slow and require an expensive metrology lab which limits their use to offline applications. A large amount of time is required to remove the vehicle from the line, fixture and align it on 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 1,000 vehicles can be built each day in a single automotive plant.

Traditional inline systems can have over 100 fixed sensors. These fixed sensors are demanding to install and maintain and do not provide ‘absolute measurements’ of the features in the car’s coordinate system. 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.

Recently inline inspection systems have been moving towards robotic based solutions which are flexible but rely on the robot for positional accuracy which limits their performance.

The Laser Radar

Nikon’s Laser Radar provides a unique alternative to the shortcomings of the traditional inspection methods. The device 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 device 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. This robust measurement ability means that the device can be used for both BIW and end of line flush and gap inspections on finished cars.

In addition, the device also has a large measurement range (up to 50 m for the MV350), allowing it to easily measure objects that have the size of cars, trucks, and other large vehicles.

Line Side Inspection

Laser Radar inspection stations can be installed line side. A station consists of one or more laser radars mounted on 6-axis industrial robots. This type of robot is common place in automotive production facilities, is very robust and can easily handle the payload of the device.

The robots are used to automatically reposition the device so it can inspect areas that are hidden from the line-of-sight of a single device 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 device to an alternate location will make these features visible again without the need for multiple sensors.

After the robot repositions the Laser Radar, the device 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 repeatedly position the device.

In each location the device can measure dozens of features on the vehicle. These measurements are pre-programmed 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 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 device, 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.

Bringing Accuracy To A New Level

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 device 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 device makes it ideal for inline inspections; different vehicle models on the same assembly line are simply a new inspection program.

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