An optimized production flow is no longer a luxury, but rather it has become a necessity these days in order to survive. Up-to-date engineering helps to save costs in order to make the plant is utilized to an optimum and best possible use is made of the raw materials. The Esterer WD GmbH, a specialist in the design and construction of saw mills with production facilities in Rottenburg and Altötting, has been concentrating its activities the recent years on PC-based control systems. As a result the latest example of this is the sawing and chipping line put into operation for the Hermes Holz GmbH that was extended in 1997.

Founded in 1922 in Stadtkyll, the Matthias Hermes Holz GmbH relocated on the occasion of its fiftieth anniversary to the nearby industrial park. An entire bandsawing and chipping line was installed by the Esterer WD GmbH in two stages of construction, in 1991 and 1997. The first stage of construction, a bandsawing line including a chipping unit, was put in gear commissioned together with four bandsaws in 1991.

A procedure for rotating the trunk must be applied in order to cut the wood tailor-made as construction timber. A trunk has to be fed into the sawing unit at least two times during this process. The second stage of construction was to install a second band saw and chipping line as well as a trimming band saw unit. An increase in output was possible by the expansion made in the plant, from the 100,000 cubic meters before the extensions to approximately 150,000 cubic meters today, and with a greater flexibility in the manufacturing facilities.

Producing without gaps in the production flow
The entire plant can be operated by one person from one control desk, to where all information is forwarded for the visualization software. Together with 13 settings for the closed-circuit surveillance cameras, this software gives the operator a complete overview and hence control, of the system that totals to nearly 100 meters in length. The information from roughly 5,000 inputs and outputs in the system, collected in decentralized sub-distribution stations equipped with Interbus modules, are transmitted via a single cable to a PC control card inserted in a PC.

The visualization software shows the operator the current positions of the wood in the production line. In addition to this, localized defects and malfunctions can be blended in to the split display.

This PC card of the type PC CB-COP, with its own processor, executes the entire automation program. The software was generated by the company of Holz-Industrie-Beratung, Rosenheim (HIB), which forwards all information of relevance to the visualization software. Individual tracking of the logs throughout the plant is possible as well.

Optimized production
The software enables optimization of production routines due to the feed by the frequency-controlled drives can be individually adjusted as a function of the trunk diameter up to a maximum rate of 90 m per minute. It is possible to individually adjust the conveyor speeds in single sections of the transportation system since the conveyor units in the plant are equipped with frequency converters as well, so that any gaps in the production flow can be closed by accordingly increasing the transportation rate. Virtually uninterrupted tree-trunk cutting is made possible by this method.

Interbus links all the units in the production facilities in order to ensure a smooth production flow, from the infrared-measuring station for the tree trunks through to stacking the cut timber and planks being discharged. The big advantage here is the considerably low installation work required as the individual stations only have to be connected only by the Interbus cable using a D-sub connector.

Not only the frequency converters and the Stegmann absolute rotary transducers are directly linked with the system, also the subordinate PLCs that assume the positioning tasks for the servo-assisted axes, and the transfer of important information to the main system. On the one hand, inclusion of the first stage of construction in the whole system was made very straightforward by the decentralized installation, whereas on the other hand, the costs required for the startup and get into operation were considerably lower for the machinery and plant manufacturers, as were the times - by as much as 50 % in comparison with parallel cabling.

The PC as the control-system computer
There is a particularly high potential shown by the PC card for savings to the machinery manufacturers. Where so far a computer was used for the visualization and a PLC system for the control tasks, an integrated solution is now possible. The computer, already available for visualization routines, is acting at the same time as the basis for automation of the entire plant.

The raw timber is fed into the chipper by feed drives. There are two electrical cabinets directly connected to the equipment in the rear. The decentralized I/O modules make electrical installation really comfortable.

It is also possible for the maintenance fitter and the plant operator to inquire all conditions in the plant at the central computer by means of CMD software (Configuration Monitoring Software); any anomalies are displayed directly. These excellent diagnostics and monitoring functions minimize any downtimes at the plant attributable to malfunctions and defects.

Conclusion
For the Esterer WD company that has already applied this concept using Interbus in a numerous plants, the sophisticated, PC-based control-system engineering from Phoenix Contact constitutes the right step into the future.