The invention relates to a method for the processing of wood according to the preamble of claim 1.

Recently, wood processing and its drying process in particular are controlled by monitoring indirect quantities, such as relative humidity of air and dry and wet bulb temperatures of air. There are various kinds of wood moisture meters on the market, but their accuracy, reliability and range of measuring information are not sufficient for continuous measurement and the adjustment of the drying process.

The recent drying process is adjusted by blowers having automatic blowing direction reversal, radiators and ventilation ducts. A conventional adjustment and control apparatus of the drying process of wood includes moistening devices of drying air (high-pressure water spraying or vapour), sensors for measuring the temperature and relative humidity of air as well as a measuring system of wood moisture and a control system of the drying process. In the conventional adjustment and control method of the drying process of wood, each wood species and various timber grades and dimensions are compiled their own empirical drying program i.e. drying formula. According to the drying formula, the drying temperature and the relative humidity of air in the drying plant are automatically adjusted as the drying progresses. Drying times are dependent on target quality, wood species and its density, initial and final moisture, and temperature. The typical drying time from a freshly-felled tree to moisture of less than 10% varies from a few days to several weeks depending on the wood species and the dimensions of timber being dried.

A problem in processing wood, such as sawing and drying, is that part of timber being or having been sawn or being or having been dried does not fulfil the quality and structural requirements set for the blank of the end-product being manufactured and it is not good enough for the desired use. However, recently used monitoring methods of wood quality and structure do not enable real-time analysis during the treatment process of wood. Due to the insufficient monitoring methods of wood quality and structure, almost all timber intended for end-product manufacturing is treated in the sawing and drying processes, whereby part of timber is unnecessarily treated. Primary in the drying of wood are by no means the moisture and temperature of air but the fact that wood being dried is not damaged as a result of drying and that the final moisture of wood is even enough i.e. the wood has a low moisture gradient. The aim is to provide wood with a solid structure and having as low as possible moisture distribution, gradient, and a desired moisture percentage.

An object of the invention is to provide a method for processing wood by means of which method it is possible to monitor timber and its properties for the whole process and avoid the damaging of wood. A further object of the invention is to introduce a method by means of which it is possible to remove possible damaged timber at a stage as early as possible. Additionally, an object of the invention is to introduce novel programming as a measuring and adjusting method of wood processing and the drying process and in modifying timber properties.

The object of the invention is achieved with a method for processing wood, which is characterised by what is presented in the claims. In the method according to the invention, the structure of a piece of wood and its properties independent of each other and the processing of wood are monitored and measured at different stages of the wood treatment process with measuring ways independent of each other, the drying process is monitored and the drying process is adjusted considering the above measuring results independent of each other. When the wood and its properties and the process at its different stages are monitored and measured with measuring ways independent of each other, it is possible to observe in real-time the moment and prevailing conditions in which the damaging of timber starts. When the moment and conditions are known, the aim is to avoid the creation of such situations. The objective is to create no conditions for the splitting up and/or other damaging of wood.

In an advantageous embodiment of the method according to the invention, the properties independent of each other of a piece of wood and the structure of the piece of wood are monitored and measured before drying the piece of wood with at least two measuring ways independent of each other before sawing and after sawing, before drying the wood.

In an advantageous further embodiment of the method according to the invention, the properties independent of each other of a piece of wood and the structure of the piece of wood are monitored and measured during drying the wood with at least two measuring ways independent of each other. In an advantageous further embodiment of the method according to the invention, the properties independent of each other of a piece of wood and the structure of the piece of wood are monitored and measured after drying the wood with at least two measuring ways independent of each other. In an advantageous further embodiment of the method according to the invention, pieces of wood are sawn in a saw device and the properties independent of each other of the piece of wood and the structure of the piece of wood are monitored and measured with at least two measuring ways independent of each other before sawing the piece of wood and after sawing, before drying the wood. When analysing each product blank before and after each sub-process, before the sawing process after the sawing process during the drying process and after the drying process, it is possible to improve the total efficiency and productivity of the treatment process by processing only the part of material, which fulfils the quality requirements set for the end-product being manufactured. The part of wood material which does not fulfil the quality requirements can be removed from the process already when observed, whereby there is no need to treat this part of timber any more.

In an advantageous further embodiment of the method according to the invention, electrical impedance spectroscopy devices analyse and monitor the structure and the moisture gradient of wood at different points. Electrical impedance spectroscopy (EIS) means measuring the impedance (alternating-current resistance) of the target on one or more frequencies. The result is one or more impedance values, which provide data on the structure and properties of the target. Impedance is the ratio of the amplitude of voltage U prevailing over the circuit and the amplitude of current I passing through it. As current and voltage in alternating current have a phase angle, they are represented with complex numbers in the circuit analysis. Thus, their ratio, impedance, is also a complex quantity, i.e., impedance has a real part (resistance R) and an imaginary part (reactance X). Impedance, like other complex quantities, can alternatively be represented in polar form by means of the phase angle and amplitude. Electrical impedance spectroscopy has been used in various applications one of the most important of which is studying biological matter e.g. in medical science. By means of EIS technology, it is possible to monitor the structure and the moisture distribution, gradient, of wood in real time. In other embodiments of the invention, the structure and/or moisture of wood can be analysed and monitored with some other method and apparatus known as such and suitable for the purpose.

In an advantageous further embodiment of the method according to the invention, an acoustic emission measuring device monitors micro cracks possibly created in the drying process. Acoustic emission (AE) is based on the measurement of elastic high-frequency (150-160 kilohertz) waves in a structure. Waves are created and they are measurable when a solid structure is exposed to mechanical load and, particularly, when changes occur in the structure of the material being examined. Emission is perceivable when waveguides connected to a piezoelectric sensor are installed in the measurement target. The sensor registers changes in the waves caused by cracks, leaks or friction. In the drying of wood, AE technology allows to monitor the micro cracking of wood as wood emits ultrasonic- frequency sound in connection with micro cracking. In other embodiments of the invention, the structure of wood and micro cracks formed in it can ^x be analysed and monitored with some other method and apparatus known as such and suitable for the purpose. In an advantageous further embodiment of the method according to the invention, microwave resonators analyse the amount of water in wood at different points. Microwave resonator analysis (μWR) is a measuring method in which a microwave resonator observes the amount of water in wood by measuring an oscillation frequency of a resonator contained by wood. The peak of oscillation intensity occurs on frequencies the lower the more water the wood being analysed contains. The measurement can be performed as wood moves in the production process. The microwave resonator analysis can measure the amount of water contained by wood being dried and having been dried before and/or after drying. In other embodiments of the invention, the amount of water in wood can be analysed and monitored with some other method and apparatus known as such and suitable for the purpose.

In an advantageous further embodiment of the method according to the invention, during the sawing and drying of wood, the structure and properties of wood as well as the conditions of the process are monitored and measured at different stages and at different points of processing wood and the data is saved and a process/drying chart describing the properties of wood material and their changes is compiled. In an advantageous further embodiment of the method according to the invention, the drying and modification process of wood is adjusted by means of the wood process chart. The process chart shows in a table format the adjustment parameters of devices controlling the drying and modification of wood and the monitoring values controlling the progress of the process. Each row of the chart shows the stages following each other in the drying and modification process of wood. There can be one or more stages depending on the wood species being dried and modified, dimensions, initial values, and the desired end-result. The stages implement the drying and modification process from start to finish, e.g. the heating stage, the drying stage and the cooling stage. The transfer from one stage to another takes place when any one or more quantities measured from the process or calculated or averaged from measuring results, the trigger quantity, or their combination reaches a value determined for each process stage, the trigger value. The trigger quantity or quantities and their values and conditions between the trigger quantities are shown in the process chart for each stage separately. The adjustment of the process takes place based on information measured or calculated from the process. Information measured or calculated from measuring results, used for the adjustment of the process and transferring from one stage to another are e.g. wood species being dried, length, width, thickness, initial moisture, targeted final moisture and gradient, hardness, strength and torsional rigidity, targeted drying time, during drying wood temperature, moisture, gradient, mass, amount of water, compression, compression speed and surface pressure, drying chamber or chamber part dry bulb or wet bulb temperature or relative humidity, time, values received from AE, EIS or μWR measurements, and hydraulic pressure. The adjustment of the drying and modification process takes place by adjusting drying-stage temperature, relative humidity, drying-air direction and intensity and wood compression, compression speed and compression pressure in each stage described by the process chart. By means of the process, it is possible to monitor and adjust e.g. wood moisture content, moisture distribution, single wood blank moisture distribution, gradient, hardness, strength and torsional rigidity and thickness. There can be several different process charts of which a chart is chosen for the particular use.

In an advantageous further embodiment of the method according to the invention, a genetic algorithm and genetic programming are used as the measuring and adjustment method of processing wood and in the modification of timber properties. The invention advantageously applies the genetic algorithm (GA) and genetic programming (GP) as the measuring and adjustment method of the drying process of wood and in the modification of the properties of dried timber. It is common for the genetic algorithm and genetic programming as the adjustment and control method of the drying process that genetic algorithms are heuristic optimisation methods imitating the evolution mechanisms of nature. They are applicable to tasks in which the solution space is very large (e.g. large combinatory tasks) and in which even a rough optimum is enough as the solution. Due to the rapid increase in the calculation capacity of computers, the application possibilities of genetic algorithms have also expanded greatly during the past decade.

Advantages and additional values provided by the genetic algorithm and genetic programming in the measuring and adjusting technique of the drying process of wood are the following:

- Conventional mathematical analysis does not or cannot offer an analytical solution. As adaptive methods, GA and GP adapt to changes occurring in the drying process or changes in the wood species being dried or its dimensions. The process improves without external intervention by means of real-time optimisation or machine learning. The adaptation is continuous.

- Internal relations between relevant variables are poorly understood and the genetic algorithm and genetic programming improve this situation.

- Finding the size and form of the final solution to the problem is a key part of the problem.

It is possible to present a common model on how the genetic algorithm (GA) and genetic programming (GP) are used for improving the adjustability and speed of the drying process, for improving the quality of timber and for modifying its physical properties. Then, an initial situation (initial population) is created by measuring the properties of the batch of timber being dried in the initial situation, random process adjustment values and parameters are determined, the drying process is followed through by means of chosen initial parameters using the functions, variables and constants of the problem, the batch of dried wood is evaluated based on how they solve the problem and how the measured physical end-results correspond to the expected values, a new population of computer programs is created based on previous data, the best existing program is copied, new computer programs are created by means of mutation, new computer programs are created by means of crossing and the best computer program occurring in any population is chosen, i.e., the best solution so far is chosen as the result of genetic programming. When using the genetic algorithm and genetic programming, an approx ⁱ mate solution is approved in the adjustment and control method of the drying process, because it is the only solution, which will probably ever be provided. There are lots of data readable on a computer, which require reviewing, classifying and combining. Small improvements in the performance are routine to measure (or easily measurable), but they are still important from the viewpoint of the total end- result.

In other applications, it is also possible to use other known programming methods with which a program is compiled for considering the values measured in processing wood and for the continuous adjustment of the process.

Primary in the treatment and drying of wood is that the wood being dried is not damaged as a result of treatment and/or drying and that the final moisture of wood is even enough and the wood has a low moisture gradient. The object of drying is wood with a solid structure and having as low as possible moisture distribution, gradient, and a desired moisture percentage. To provide this object, the above- described electrical impedance spectroscopy (EIS), acoustic emission (AE) and microwave resonator (μWR) monitoring methods and/or other alternative methods offer a possibility to observe in real time the moment and conditions prevailing when the damaging of wood starts. When the moment and conditions are known, the data are saved and considered in the future and the aim is to avoid the creation of such situations.

The monitoring techniques of the drying process are not useful until both the mutual and total effects of observed process values on the changed properties of the wood being dried are known. This is continuously established according to the method by monitoring and analysing the structure of the piece of wood and its properties independent of each other and the drying process at different points with measuring ways independent of each other.

Wood is a non-homogenous material and there are thousands of wood species all having different physical properties. When the object is to modify at least part of these species at least approximately to specific physical properties (surface hardness, strength, moisture, torsional rigidity, age resistance without chemicals harmful to the environment), such an optimisation theoretical situation is reached which can be solved e.g. by the above methods using the genetic algorithm (GA) and genetic programming (GP). The invention will now be described in more detail with reference to the accompanying drawings in which

Fig. 1 schematically shows an oblique side view of a treatment and drying apparatus of wood, Fig. 2 shows a cross-section of the principle of the drying apparatus included in the apparatus according to Fig. 1,

Fig. 3 schematically shows a measuring device of electrical impedance spectroscopy and/or microwave resonator analysis, and

Fig. 4 shows the principle of a microwave resonator and the measurement of the amount of water in wood.

Fig. 1 shows a treatment and drying apparatus of wood. It includes a saw device 1 for sawing timber and a drying apparatus 2 for drying sawn timber. The apparatus includes transfer devices known as such for transferring timber to the saw device, from there to the drying device and further from the drying device, but they are not shown in the figures.

In the saw device, timber is sawn to desired size and, after the sawing, wooden boards 6 are set side by side and on top of each other onto intermediate supports before the drying device and are transferred to the drying device according to Fig. 2 in which timber is dried in a way known as such. The drying device according to Fig. 2 includes a chamber 8 in which there are press devices 9 between which timber is controllably compressed during drying, heating devices 10, such as heating coils, for adjusting the temperature of air during drying, and a blower 11 for circulating air.

Furthermore, the apparatus includes several measuring devices, which monitor and measure the structure of the piece of wood and its properties independent of each other and the drying process at different points with measuring ways independent of each other. In this embodiment, the apparatus includes four electrical impedance spectroscopy devices (EIS) 3; a first electrical impedance spectroscopy device is located before the saw device of timber and it is arranged to analyse the structure and moisture gradient of timber being sawn, a second electrical impedance spectroscopy device is located between the saw device and the drying apparatus and it is arranged to analyse the structure and moisture gradient of sawn wood, a third electrical impedance spectroscopy device is located in the drying apparatus and it is arranged to analyse the structure and moisture gradient of wood being dried during drying, and a fourth electrical impedance spectroscopy device is located after the saw device and it is arranged to analyse the structure and moisture gradient of dried wood. An acoustic emission measuring device (AE) 4 is located in the drying apparatus and it is arranged to monitor micro cracks possibly created in the drying process. The apparatus further includes three microwave resonator devices (μWR) 5; a first microwave resonator device is located before the saw device and arranged to analyse the amount of water in wood being sawn, a second microwave resonator device is located between the saw device and the drying apparatus and arranged to analyse the amount of water in sawn wood and a third microwave resonator device is located after the drying apparatus and arranged to analyse the amount of water in dried wood. The positioning and number of these devices can vary in different embodiments of the invention.

Fig. 3 schematically shows the transfer of one board through a measuring device. The measuring device can be an electrical impedance spectroscopy device or a resonator analysis device or one device can include both measuring devices.

Fig. 4 shows the principle of resonator analysis in which the microwave resonator 5 observes the amount of water in wood by measuring an oscillation frequency of a resonator contained by wood. The measurement can be performed as wood moves in the production process. The peak of oscillation intensity occurs on frequencies the lower the more water the wood being analysed contains. By measuring the width of the resonance peak, it is possible to determine the change in the conductivity of the piece being measured and to determine the amount of moisture contained by the piece.

When using the apparatus according to Fig. 1, timber is brought to the vicinity of the apparatus. Before feeding the timber to the saw device, the timber is analysed with the electrical impedance spectroscopy device and the microwave resonator analysis device. When the timber has been sawn, each sawn piece of wood is analysed with second electrical impedance spectroscopy and microwave resonator analysis devices between the saw device and the drying apparatus. During drying, the timber being dried is analysed with a third electrical impedance spectroscopy device and an acoustic emission measuring device. When the timber has been dried, each dried piece of wood is analysed with an electrical impedance spectroscopy device and a microwave resonator analysis device located after the drying apparatus. Timber being sawn, timber having been sawn, timber being dried and timber having been dried are analysed according to the method with measuring ways independent of each other. Thus, reliable analysis and data on the properties of timber during the whole process and at different stages are obtained. Damaged timber can be removed from the process immediately after having observed it. The data of the process are saved and a program in a way described above which can be utilised in the processing of similar and possibly also differing wood materials in the future.

The invention is not limited to the described advantageous embodiments, but it can vary within the scope of the inventive idea presented in the claims.