Test & measurement
HIGH PRECISION INSPECTION OF SURFACE DEFECTS IN AUTOMOTIVE APPLICATIONS
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n increasing number of industrial applications require reflective surfaces to be recognised and measured. For example, in electronics manufacturing,
smartphone production and in the automotive industry when producing mirrors or checking for paint defects on finished car bodies. In order to detect a fault or defect on these surfaces, OEMs require high precision measuring systems that detect deviations in the surface structure to sub-micrometer accuracies.
HIGH PRECISION SURFACE SCAN USING DEFLECTOMETRY
For all these fields of application, Micro-Epsilon has developed the reflectCONTROL sensor series, which is based on the deflectometry measuring principle. Here, the sensor displays a sinusoidal striped pattern via a monitor, which is reflected into the sensor’s cameras via the surface of the object being measured, for example, a car body. The resulting phase images can be used to calculate ‘kernel’ images based on the measured variables of base intensity, amplitude and curvature. Deviations on the surface are detected, processed by the software and displayed in the reflectivity and curvature images.
HIGH RESOLUTION MEASURING SYSTEM The reflectCONTROL Automotive measurement system from Micro-Epsilon (also known as PSS 8005-D) has a measurement area of 367.5 mm
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3D inspection systems can visualise surfaces down to the smallest detail. In the automotive industry, for example, the smallest paint defects or inclusions in the paint result in costly reworking. Inspection systems are now available that detect defects quickly and reliably, thereby reducing costs, says Glenn Wedgbrow, business development manager at Micro-Epsilon UK.
x 823.4 mm. The sensors measure the smallest of defects at a resolution of 185 µm and operate with a measurement data acquisition time of 400 ms. The supply voltage is 24 V DC with a power consumption of less than 200 W. This high precision, high resolution benefits leading vehicle manufacturers in paint defect inspection. In the past, these companies relied on light tunnels where skilled workers would use fixed lighting systems and cameras to detect defects in the paintwork. Alternatively, systems whereby the car body would move past static sensors on a conveyor belt were also used to detect defects. However, both options are very error-prone for different reasons.
SHORTER CYCLE TIMES
This is why car manufacturers now rely on measuring systems such as reflectCONTROL, where the vehicle chassis is brought into a fixed position. The sensors are attached to robotic arms and move across the bodywork. Micro-Epsilon chose this method because it achieves the lowest error rate and the required cycle times – the time that elapses between the inspection of two vehicles – can be met.
Two to four robot arms, each with an integrated sensor, work at each inspection station – allowing the entire chassis to be measured. For very short cycle times, two stations with four robots each have proved successful – but Micro-Epsilon can offer solutions for all desired cycle times. In order to accelerate and decelerate the robot arm sufficiently, it was necessary to keep the total
weight of a sensor below 50 kg, which Micro- Epsilon achieved using a carbon housing. This also increases the robustness of the overall system and protects the robot arm, which further extends its service life.
DEFECT DETECTION AND AUTOMATIC PROCESSING
With light tunnels, car manufacturers achieved a defect coverage of around 60 per cent in the past meaning around 40 per cent of defects were left undetected! With reflectCONTROL, fault coverage of almost 100 per cent is now possible. This high fault coverage is due to outstanding defect detection and automatic processing. First, the vehicle is measured from one measuring position to the next and any defects found are projected back onto the vehicle surface. A defect can be localised at +/- 3 mm on the vehicle surface. 3D features such as height, depth and volume are added to each defect using 3D reconstruction, which is unique on the market. All collected data is saved in an XML file and so is available to the vehicle manufacturer at any time. Once the defect has been detected and localised, automatic processing can begin, which Micro-Epsilon implements together with its partner companies ASIS and Virtek Vision. This is carried out using additional robots with active force
March 2025 Instrumentation Monthly
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