nokra also implemented the safety concept – including CE marking and the integration of the system into the production process – developed in cooperation with the consulting institute BIT e.V.
The system was installed during scheduled downtimes. Consequently, there was no interference with regular production. As nokra supplied the system with the laser source and the camera firmly connected within a common housing and in a pre-calibrated state, no calibration effort was required. This saved much on commissioning time.
nokra’s exceptional know-how and longstanding experience as a supplier of optical measuring systems for the steel industry were paramount for the success of the project. This is demonstrated, among others, by the sturdy mechanical design of the steel structure. nokra was also extremely flexible and supportive in customizing the system to the constraints and specific circumstances in the plate mill, and ready to accept the responsibility for the complete project, including the travelling steel structure and the integration of the system into SMGB’s infrastructure.
The test run of the nokra system went very smoothly. Since the end of November 2019, the system has been operating as a fully integrated asset of the plate production process.
Operation with the newly integrated system
The plate transfer within the Mülheim plate mill is handled by a warehouse management system. When a plate is placed on the cooling bed, the system enters the plate ID number to assure reliable material tracking during the contour measuring process. The operator at the cooling-bed control station selects the plate to be measured on his screen and sends the specific plate data to the system.
Additionally, in order to rule out the risk of mixing up material, he doublechecks the plate number via images taken by two cameras mounted on the measuring beam. As soon as the plate has been properly positioned within the measuring area, the plate data is transmitted to the system and the operator starts the measurement with the push of a button. The system starts automatically. While moving along the length of the plate, it measures the complete plate geometry. It stops immediately as it recognizes the plate end and returns to its parking position.
As soon as the measuring process has been completed, the software calculates the plate geometry, length, width and the cropping cuts at the plate head and tale. The complete contour is graphically displayed at the control pulpit. Then the measured data is transmitted to the higher-level product data and information system “PRODIS”, which calculates the cuts, taking into consideration safety allowances, sample cutting and the plate sizes specified in the customer order.
The sensor units developed by nokra for the light-section process project laser lines onto the plate surface, each one covering a width of 1,150 mm. While the measuring beam is travelling above the product to be measured, the cameras arranged at an angle within the sensor units capture their respective light lines. The plate edges are determined based on the images taken by the cameras and the position of the measuring bridge along the plate length at the time each image was taken. From the measured width and length values, the software calculates the contour.
In the system installed in the Mülheim heavy-plate mill of SMGB, nokra uses lasers of different wavelengths (red and infrared) in two adjacent sensor units. This eliminates the need to offset the lines, makes the equipment more compact and exploits the full length of the cooling bed.
The height information, which is used to calculate the flatness, is derived from the angle at which the cameras capture the lines on the plate surface.
First experience and conclusions
The new system fully complies with the requirements specified by SMGB and has been performing as guaranteed by nokra. The outside contours of the plates, i.e. width and length, are measured with an accuracy of 3.5 mm and 5.0 mm respectively. The accuracy of both the contour and the flatness measurements is definitely up to expectations. The employees greatly appreciate the way the contours are visualized – how the cutting lines, the safety allowances and the sample cuts are indicated. They immediately accepted the new system.
The cutting pattern data derived from the measured values can also be viewed and used in the downstream processing stages. The availability of digitized geometrical data enhances statistical process control and is extremely useful in performing detailed evaluations and achieving process optimizations. It is possible to systematically analyze the effects of certain materials or geometries on the production process. Also in-depth analyses of historical data can help to further optimize the production process. It is possible to analyze the effects of individual material grades on the rolling process, for example, or whether certain plate dimensions may require special attention.
To enable high-precision alignment of the coordinates of the five sensor units, a calibration block in hard stone has been installed at the parking position of the measuring bridge in front of the cooling bed. It has proved useful to perform an alignment once per shift and whenever the ambient temperature changes by a specified value. For the alignment, the laser lines are measured relative to one another and automatically adjusted, if necessary. The alignment is an entirely automatic process.
The measuring bridge is completely encapsulated. Therefore, apart from occasional removal of dust, the optical equipment does not require any other cleaning measures. The maintenance staff greatly appreciates the fact that the parking position of the system is next to – not above – the cooling bed. This means that the measuring bridge is easily accessible even during running production.
In the event of a power supply failure, the control computer of the measuring system is buffered by a UPS system. It shuts down automatically after a few minutes without power, and reboots and restarts all necessary programs – also fully automatically – as soon as power is back up. All this takes place without any intervention by the maintenance staff.
The first months of productive operation have shown that the contour and flatness measurements of the individual plates work extremely reliably. Availability of the system has been excellent. These results prove that it was the right decision to employ a system that uses a measuring beam that travels above the plates while these are lying still on the cooling bed. Also the algorithm that calculates the cuts has proved highly successful in maximizing the yield and minimizing waste.
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