Around three million cubic meters of wood are processed into almost 40 million square meters of laminated chipboard every year at the Fritz Egger chipboard plant in St. Pölten-Unterradlberg. Lined up end to end, that would be half the circumference of the earth. The chipboard is supplied to industry and specialist retailers.

After the panel strands are pressed and then cut to size using a multi-diagonal saw, the raw panel production department regularly measures individual panels to correct any dimensional deviations. Until now, this was done exclusively manually: either by ejecting so-called good panels from production or by measuring panels in the system, for example in the cooling star turner.

Previously, Egger checked the ejected panels by hand using a tape measure and then sent them to scrap. If the measured values differed, the operator had to enter and confirm the corresponding correction values at the saw. In the meantime, however, numerous panels with the incorrect measurements had already entered the system. After repositioning the saw, the operator had to move another panel into the reject area to check whether the desired result had been achieved. If the panel still did not meet the specifications, the saw had to be adjusted again.

This process took between a quarter and half an hour. In order to eliminate the serious safety-related disadvantages of this procedure, both the plant manufacturer and supplier Siempelkamp and Egger wanted a more automated solution for measuring. "The previous technical solution for measuring the boards behind the multi-diagonal saw was not state of the art," says Dr. Frank Otto, project manager at Siempelkamp Logistics & Service, describing the initial situation. "In addition, the multi-diagonal saw in our plants is increasingly cutting in tandem, triple or quattro mode, i.e. with two or more sawing units. The process of manual panel measurement in conjunction with manual correction of the cutting values in the event of dimensional deviations is proving to be too complex and time-consuming for our customers, not to mention the safety-related shortcomings."

The solution: The panel measuring system is housed within the machine system so that the saw can be corrected immediately after dimensional deviations occur and the operator can react quickly to process changes in order to stabilize the processes and ensure the quality of the manufactured products.

Measuring the panel geometry

In the production of chipboard, the forming and press line is the process-determining system unit within a complete plant and is decisive for its capacity and the quality of the products. For this reason, the downstream machines should provide a performance that is adapted to this in order to avoid bottlenecks. Ideally, for example, a system for measuring the panel geometry should be installed downstream of the saw, preferably inline: Siempelkamp's 'SicoCam' inline panel measuring system measures the panel length and width and also calculates the diagonals and angles at the four corners. In this way, trimming and cross-cutting can be optimized and waste minimized.

With inline panel measurement, cameras from Sick record every panel corner during production. The measurement data is further processed with software support in the form of width, length and diagonal dimensions.

© Sick

The details are as follows: The individual panels cut to length from an endless strand are measured as they pass along a transport track. Four programmable 2D 'Inspector65x' cameras from Sick are mounted on a gantry above the conveyor, while the cameras at the rear of the conveyor are mounted on a movable carriage in the gantry. This carriage is used to adjust the camera system to the different panel lengths. The adjustment accuracy is in the 0.01 mm range. A small photoelectric sensor detects the front and triggers the recording or triggers the cameras.

"The SicoCam gantry is simply placed over a conveyor belt or roller
conveyor belt or roller conveyor and the panel is measured as it arrives," says Dr. Frank Otto, describing the setup. This means that there is no mechanical connection to the existing system. This decoupling means that neither modifications to the existing machine technology nor functional changes nor braking of the plate are necessary. The gantry can be set up during operation and only requires a short standstill.

Communication via Ethernet

The measured coordinates of each individual camera are transmitted to the evaluating PLC via Ethernet. The overall evaluation of the measurement result takes place there (taking into account the position of the camera carriage); a data connection to the higher-level system PLC is also possible. The measurement data is processed and stored in a data module. Measurements can be taken within 0.5 s.

A screen on the system and in the press control room visualizes the measurement results, which are archived for a period of four weeks. Once the main PLC has been adapted, the measured values can also be used for automatic correction of the diagonal saw (length and diagonal correction). The commission data provided by the higher-level system PLC is available to the measuring system for automatic adaptation to the product geometry being processed.

A question of software and hardware

The "SicoCam" gantry with four programmable 2D cameras is positioned above the conveyor belt or roller conveyor without any mechanical connection to the system.

© Sick

Measuring the plate geometry requires, among other things, height compensation, as the plate is transported at speeds of up to 4 m/s. The panel is under tension when it comes out of the press and is also sometimes slightly curved downwards or upwards. To compensate for these factors, it is necessary to use lasers at each plate corner and to program the Sick app accordingly, which can be used to implement individual applications and user interfaces based on programmable cameras and optical sensors.

Siempelkamp uses the programmable cameras of the 'InspectorP6xx' product family, in which optics, lighting, evaluation and interfaces are integrated and customizable. The 'Halcon' image processing library is already installed.

The savings potential

According to Siempelkamp, it is difficult to precisely quantify the savings potential resulting from the inline measurement because it depends, among other things, on the number of commission changes and the associated material or cutting allowance. "For plants for the production of medium-density wood fiberboards, we assume savings in the six-digit range in euros per year for the annual production of an average board, which are easily possible simply because the material allowance can be reduced by 10 mm," explains Markus Gropp, branch manager of Siempelkamp Logistics & Services.

Savings are not only achieved by reducing the cutting allowance, but also by using a higher proportion of A-quality boards. Since the measuring system immediately indicates deviations from the target dimension, the saw setting can be corrected immediately. This reduces the proportion of B quality, which does not save the full material price, but does reduce the price difference between A and B quality. And last but not least, not as many panels are moved to the reject area and measured manually - resulting in significantly fewer rejected panels each year.

"We could completely automate the plant with the system," says Markus Gropp, describing the further development. "At the moment, we have a stand-alone measuring system. The saw is only adjusted when the operator wants it to be. He can see on site how the saw is reacting and whether he needs to make corrections, because he has the values he needs to correct the saw fully calculated in the saw mask in front of him."

Author:
Mohamed Hassoun is Technical Industry Manager Factory Automation at Sick in Waldkirch.