Automatic systems for log sorting lines
Today it’s difficult to imagine a modern sawmill with a monthly production program of several thousand cubic meters of sawn timber without a log sorting line. These lines are the first part of the technological cycle of sawing, having regard to the great need for metal and because of their large footprint, they require a big investment in their construction and maintenance. It’s convenient to add to the main functions of sorting line (acceptance of round timber from suppliers and preparation of raw material for cutting) the sorting based on differentiation of the butt part and the top part, and by that to exclude the log turner from the equipment of log supplying to the workshop. In the struggle to optimize the labour costs, such sorting lines are being equipped with barkers. It’s clear that such additional functions have not only advantages, but also disadvantages, such as debarked and oriented logs require more space for the stacks, because the height of the stack in this case would be significantly smaller. The main function of the line is still the sorting of raw saw logs by sawing schedule. The sawing schedules depending on the type of sawmill equipment may have different fragmentation- from 2 to 0.5 cm. The efficiency of the sawing production, in general, depends on the quality (accuracy) of log sorting by diameter. Taking into consideration the cost increase of raw materials in the total cost of saw timber, the requirements for the measuring system are becoming tougher every year, and such requirements are not accidental – in fact, the decrease of sorting quality of sawing log by 1% leads to increase of the useful output of sawn timber by 0.15 … 0.2%.
Productivity of the log sorting line, in general, depends on the reliability of machinery and the irreproachable work of all the units starting with single-piece feeding, ending with an accurate and uniform log stacking in the pockets. The increase of productivity by 15 – 20% can be obtained at the stage of single-piece feeding. For this purpose, the feed table is equipped by orienting roller orientation that aligns the ends of logs in one line. The same effect can be achieved by means of automation – a laser distance measuring device, a built-in single-feeding device and a pair of position sensors at a linear log conveyor. With this equipment, you can adjust the break between log butt ends and maximize the productivity of the line.
Having regard to the fact that nowadays the requirements for the sorting accuracy are becoming tougher the use of simple one-and two-plane measurement systems with the sorting quality from 75% to 85% phased out in favour of more modern 3D systems that measure and calculate the basic geometrical parameters beams with high reliability and quality to achieve 92% … sort of 95%.
Measurement of crookedness, roundness, taperigness by 3D scanner VECTOR gives an additional effect when sorting through the special features:
- Reduction of the sorting diameter depending on the crookedness
- Screening of logs with large knots
- Auto quality – giving of a sort to the log depending on the combination of certain geometric features.
Log sorting control systems produced by “AVTOMATIKA-VEKTOR” cover this wide range of configurations, and may already be used on lines different from the constructive point of view by type of the discharging device:
- The most common type is the lines with a hydraulic kicker. The principal producers – «Ingvar Person», «Lesmashprom” with a distinctive feature of the use of double-chain conveyor and the bottom position of the pusher –ram and Hekotek – single-chain conveyor, with a side log pusher. The advantages of these lines include such qualities – such as simplicity and durability of the kicker. The main disadvantages are rigid requirements of hydraulic equipment to the oil quality, which are particularly shown up in the severe frosts (oil resinification in the hydraulic system). Also, some structural features of this kicker can lead to irregular placing in the pockets of forest thinners.
- Lines with electromechanical log kicker. Principal producers are Springer, Shilher, LesMash, FTWood and Timbermatic. Main advantage is the efficiency in a wide temperature range, the disadvantages are the complexity of the kicker’s mechanism, the existence of limit switches of kicker’s position, the need for periodic adjustment of the motor brake.
- Lines with pneumatic kicker. This type has been developed by the laboratory of the industrial log depots of SevNIIP, delivered by Plesetsk mechanical plant. At the present time, they are not produced commercially, and all newly constructed lines were designed and constructed by companies on their own (such as JSC “Bely Ruchey”, Vologda region). Advantages: simple design, durability, easy maintenance and low cost, the ability to sort the balances, starting with a 4-centimetre thickness. Disadvantages are: the possible freezing of pneumatic valve at subzero temperatures and design features that do not allow making a line with discharging on both sides.
Log sorting lines, depending on the destination and additional functions can be constructed in various configurations. Usually, the line consists of the receiving table to stack the logs, the device of piece issuance with an external conveyor, the main sorting conveyor with collector bunks, part of the conveyor to install the log measuring device with the security unit. Depending on the type of kicker (discharging device) the collector bunks can be located on one side of the conveyor – one-way kicker and from both sides of the conveyor opposite to each other (double-sided kicker). Also the sorting line may include leveling roller bed, debarkers, butt end reducers, turner, metal detector, conveyor for cleaning bark and waste. Depending on the type of actuating mechanisms the line can include a hydro station or air compressor. Electric conveyor drivers can be fitted with frequency converters, soft starters. Configuration of equipment and line components defines the requirements for line automatics and the configuration of the control system. Different sorting lines are shown below in the diagrams:
The log sorting control system can be functionally divided into two parts. The first part provides automatic log issuance by pieces, it controls the conveyor’s on / off, the power station, and ensures the correct starting and operation of actuating devices. Control is carried out by using the buttons on the operator’s control panel. The second part of the control system receives the orders from the operator about the log species and its sort, measures the log geometric parameters, makes the choice of the box, follows the log’s movement to the collector bunk and gives the signal to discharge.
Modern software requirements assume both visualization of the sorting process, database on the basis of SQL Server about the passing logs and developed report system (the report per shift, the report per lot, a report per staples, the report per downtime, report over a period, etc. ). These services allow you to organize automatic acceptance of log lots with a printout of a detailed report about the number and volume of the received logs with the quantization. Information is stored in the database server SQL and through the password, it is available for viewing in the local network, as well as via the Internet. Report viewing and printing are made through the conventional WEB browser (Google Chrome, Opera, Internet Explorer and Mozilla Firefox) and is available for viewing on the local network, as well via a password on the Internet.
The setting of the control system is done through the system of options. With their help, the operator may independently set the table of sorting – a set of qualitative and geometric features for each collector bunk. Usually, the program includes up to 8 species of wood and up to 16 varieties of quality. In addition to this, the program may include such parameters as diameters and lengths, top and butt taperigness, roundness, and the maximum diameter and crookedness.
The table can be stored on your hard drive by assigning it an arbitrary name and, if necessary, to quickly find and download in the system.ему.
At the logging enterprises with the removal of tree-length logs, the simple sorting lines are installed at the lower stock of raw materials after the slasher and designed for primary log sorting by the main group of logs for processing. In the simplest configuration, the line consists of a conveyor (log hauler) with a single-piece log feeding, kicker and boxes for the logs. The most common types of the conveyors: ЛТ-192, ЛТ-86, Б22У, and others. These lines are reliable, easy to use and for many years operate at logging enterprises of Arkhangelsk, Vologda, Karelia, Komi and in other Russian regions. The operator controls the work of the line using the automated control system. The operator visually rates the log, passing by him on the conveyor in the area of the order, and by clicking a button on the stand direct it to the collector bunk. The zone of the order is determined by the installation on the conveyor of reference photosensors from which the control system tracks the log movement and gives the signal to discharge the log to the box. The number of drives in this line is typically less than 20 pieces, conveyor speed is 60 meters per minute, the volume of processing is approximately 200 m3 per shift. The log measuring device in one plane can be installed Instead of the photosensor of reference.
This will permit to:
- Firstly, automatically sort the logs according to the geometrical parameters: the operator sets only the species and log’s sort, the distribution of logs in the boxes is going according to the sorting table, taking into account the measured diameter and length.
- Secondly, according to the results of the life’s work, the system forms the report about the quantity and volume of timber sorted by species and quality.
Video: Work of the log sorting line with the automatic download, single-piece log-feeding and the log measuring device VECTOR 3D.