TEST & SAFETY SYSTEMS
that robots, particularly if they are mobile, would introduce extra potential error in addition to that of the measuring devices they carry, and would need a reference measuring system to calibrate and realign them. We therefore came to the conclusion that a static CMM was the way to go in the production of our new car, with a twin-arm configuration and laser cross scanners providing the required speed of metrology.”
INFINITE POSITIONING LASER SCANNERS The LK HC-90 is equipped with Renishaw PHS-2 two-axis CNC wrists that enable the laser scanners to rotate continuously and have infinite positioning, unlike conventional probe heads that only adjust in 7.5-degree steps. Each scanner can therefore be angled very precisely throughout an inspection cycle to achieve optimal positioning both inside and outside the chassis to rapidly collect freeform and geometrical data. When inside the vehicle, the PHS-2
can rotate under program control to look outwards at the interior of the body work to take measurements, while the DMIS programs controlling each arm are essentially mirror images of each other, with additional movements inserted separately to address the minor differences unique to each side of the car. Meanwhile, the CMM’s Nikon
XC65DX-LS cross scanner with three laser lines captures in a single orientation and scans three times the amount of data typically acquired by a single-line laser scanner. This enables short inspection cycles and means that the sensor is unaffected by the colour or reflectivity of what is being measured. Additionally, automatic, real-time adjustment of the settings is delivered not only between successive laser stripes, but also for individual points along each line.
TWO-STAGE INSPECTION During the quality control process, AGVs deliver each Emira to the CMM from the production line for two stages of testing. The first stage occurs at the end of the framing line while the second takes place when the car is fully assembled. The CMM is able
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A Lotus Emira being delivered by an automated guided vehicle from the production line to the LK CMM to undergo stage 1 inspection
to automatically verify the vehicle’s identification number, colour, right- or left-hand drive and which stage metrology program should be run. After automatic calibration, the laser
scanners take 130 measurements around the car over the two stages to assess the accuracy of the vehicle. Suspension and engine mounting points are critical areas for inspection, while the control of gap-and-flush is especially important due to the spacing between panels impacting directly on the perceived quality of the car on the forecourt. Programs are created automatically
from CAD models of the Emira in LK’s Camio software to ensure the laser scanners move along paths that mean the surfaces being measured are always within their field of view. The low-noise point clouds captured are then filtered to produce smooth and highly detailed meshes that can be aligned to enable comparison of the measured data with the CAD model. The CMM’s inspection tools then enable intelligent feature extraction, GD&T tolerancing and profile analysis which are rapidly fed back to the
production line. According to Mackrill, the ability
to feed back data to the production line to validate and control the manufacturing process is driving the reliability and repeatability of the Emira’s dimensional quality. As a result, the LK HC-90 is helping to ensure each vehicle is built right the first time around. Not only has the machine improved
the dimensional accuracy of the Emira, but it has also been instrumental in raising production efficiency and lowering the labour cost content of the car. As such, the cell is driving Lotus’ production strategy for the continuous improvement of individual parts and the whole process with the goal of zero-defect manufacture. “The ceramic construction of the
machine provides excellent stability combined with light weight for accuracy and speed,” Mackrill adds. “LK supplied a fully configured, multi-sensor, turnkey solution complete with first-draft measuring programs and ancillaries. Only the fixtures supporting the car body were provided by us.”
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