WO2009072968A1

WO2009072968A1 - Method and arrangement for log classification

Info

Publication number: WO2009072968A1
Application number: PCT/SE2008/051389
Authority: WO
Inventors: Håkan Lindström; Simon Forslund; Ping Wu
Original assignee: A-Sort Ab
Priority date: 2007-12-07
Filing date: 2008-12-02
Publication date: 2009-06-11

Abstract

An arrangement for classifying logs (1) comprises transport means (21) for bringing a log (2) into a log support structure (24) of an analysis position (40). Transducers (50) for acoustic measurements are positionable into measuring positions at ends of the log (2). Electronic circuitry (60) of an acoustic measurement equipment and means for classifying (70) the log is connected to the transducers (50). The arrangement further comprises a dimension determining arrangement (16), arranged for determining outer dimensions of the log before the log is brought into the analysis position. The arrangement also comprises a position control (55) for controlling a coarse position in the axial direction of transducer support structures connected based on the determined outer dimensions. The position control is further arranged for performing the controlling at least partly before or at least partly concurrently to the log being brought into the analysis position. A corresponding method is also disclosed.

Description

METHOD AND ARRANGEMENT FOR LOG CLASSIFICATION

TECHNICAL FIELD

The present invention generally relates to handling of saw logs, and in particular to a method and means for classification of logs based on their material properties.

BACKGROUND

Industries based on biological material, such as the sawmill industry, are characterized by using raw material with a large natural variation, which leads to a large variation in the product quality. Therefore, for the sawmill industry, standards defining requirements on construction lumber with regard to form stability, drying distortion, elasticity, strength, etc have been defined (e.g. in Swedish and International standards). In parallel, there are also grading standards for visual appearance quality of sawn lumber in terms of allowance and size of knots, rot, cracks, resin, discoloration, or other visual defects (e.g. in Swedish and International standards). In view of this, there is a general need in the sawmill industry for appropriate procedures for determining wood properties in order to grade or classify wood products. In particular, it would be desirable to be able to presort logs in objective property classes to allow better utilization.

In the published international patent application WO2007/011296, devices and methods for classification of saw logs are disclosed. In this system, classification is based on combined acoustical measurements of different kinds. Such acoustical measurements presented are the measurements of transit times of elastic wave propagation and the measurements of resonance frequencies in the logs. The setups for both types of measurements consist of transmitters sending acoustic signals into the inspected log and receivers receiving the acoustic signals that propagate through the log. Transit times in different parts of the log are compared to resonance measurements and form a basis on which classification is made. For making the transit time measurements, impulse transmitters are provided at a number of positions around the log in the vicinity of one end of the log. Receivers are provided at corresponding positions close to the opposite end of the log. The transmitters and receivers are provided in a radial direction through the bark of the log into the outer rim of the wooden part in order to transmit or receive acoustic signals properly. In such a way, radial gradients of impulse velocity can be obtained, which are indicative of log quality. An automatic log handling system is suggested, where the log is transported to an analysis position, at which transmitters and receivers, i.e. transducers, are positioned into appropriate position in relation to the log, measurements are performed and the logs are finally classified.

The classification according to WO2007/011296 is basically highly reliable. However, minor problems are found in the earlier proposed system configuration. Since the transit time transducers have to penetrate the bark in order to reach the wood of the log, the transducers are exposed to a high degree of wear. This may be solved by instead placing the transducers on the sawed ends. Such a configuration, however, raises other problems. The optimum position for the transducers should be close to the outer rim of the wooden part of the log. The log diameters typically vary over a large interval. Normally the largest diameters can be up to 5 or 10 times larger than the smallest ones. Fixed radial positions are not very suitable, since they have to be designed for the narrowest admitted logs. Furthermore, the logs do also exhibit varying lengths. Typical intervals could be from 2.5 m to 6 m.

Therefore, transducers need to be positioned in the axial direction individually for each log. Since the transducers are sensitive equipment, which may be destroyed if it is smashed into the log, such adjustments can not be performed with too large velocities.

In modern saw mills, a typical throughput rate can be in the order of 0.2 to 1 log/ s. All the positioning problems described here above, necessary for adjusting the transducer positions, may sum up in that the total positioning time corresponds to a significant part of the total time the log spends in the analysis position. The throughput of the measurement system may be severely limited by such times for positioning.

SUMMARY

An objective of the present invention is to improve the maximum throughput rate of logs through an arrangement for acoustical classification of logs. A further objective of the present invention is to decrease wear of transducers used for the classification measurements. Yet a further objective of the present invention is to provide fast positioning of transducers at optimal positions on logs' ends.

The above objectives are achieved by arrangements and methods according to the enclosed patent claims. In general, according to a first aspect, a method for classifying logs comprises bringing a log into an analysis position, positioning transducers for acoustic measurements at measuring positions at the log, performing acoustic measurements on the log and classifying the log based on the acoustic measurements. The positioning comprises positioning of the transducers on or at both ends of the log in an axial direction of the log and the acoustic measurements are performed between the ends of the log. The method further comprises determining of outer dimensions of the log before the log is brought into the analysis position. The positioning of the transducers in the axial direction is then actively controlled to get a coarse positioning based on the determined outer dimensions. This coarse positioning is performed at least partly before or concurrently to the bringing of the log into the analysis position.

According to a second aspect, an arrangement for classifying logs comprises a log support structure for holding a log in an analysis position and transport means for bringing the log into the analysis position. Transducers of an acoustic measurement equipment for acoustic measurements are attached to transducer support structures and positionable into measuring positions at the log. Electronic circuitry of the acoustic measurement equipment is connected to the transducers for performing acoustic measurements on the log and means for classifying the log is connected to the electronic circuitry of the acoustic measurement equipment. The means for classifying the log is arranged for basing the classifying on an output from the electronic circuitry of the acoustic measurement equipment. The transducers are positionable into measuring positions on or at both ends of the log in an axial direction of the log and the electronic circuitry of the acoustic measurement equipment is arranged for performing acoustic measurements between the ends of the log. The arrangement further comprises a dimension determining arrangement, arranged for determining outer dimensions of the log before the log is brought into the analysis position. The arrangement also comprises a position control for controlling a coarse position in the axial direction of the transducer support structures connected to the dimension determining arrangement. The position control is arranged for controlling the coarse position in the axial direction based on an output from the dimension determining arrangement. The position control is further arranged for performing the controlling at least partly before or at least partly concurrently to the log being brought into the analysis position.

Preferred embodiments are described in the dependent patent claims.

One advantage with the present invention is that the throughput rate of logs through a log classification system can be increased considerably, being in agreement with throughput rates of other parts of a saw mill.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description together with the accompanying drawings, in which: FIG. 1 is a schematic drawing of an embodiment of an arrangement for log classification according to the present invention;

FIG. 2 is a block scheme illustrating information flows in the embodiment of Fig. 1 ; FIG. 3 is a flow diagram of steps of an embodiment of a method according to the present invention;

FIG. 4 is a schematic drawing of an embodiment of an arrangement of a transducer holder used in the embodiment of Fig. 1 ;

FIG. 5 is a schematic drawing of another embodiment of an arrangement of a transducer holder;

FIG. 6 is a schematic drawing of yet another embodiment of an arrangement of a transducer holder;

FIG. 7 is a schematic drawing of an embodiment of an arrangement of a transducer holder based on passive radial positioning; FIG. 8 is a schematic drawing of another embodiment of an arrangement for log classification according to the present invention;

FIG. 9 is a schematic drawing of yet another embodiment of an arrangement for log classification according to the present invention;

FIGS. 10A-B are schematic drawings of an embodiment of an arrangement for log classification according to the present invention, based on transverse transport to and from an analysis position; and

FIG. 11 is a block diagram illustrating principles for redundant dimensional measurements.

DETAILED DESCRIPTION

Throughout the present disclosures, equal or directly corresponding features in different figures and embodiments will be denoted by the same reference numbers.

In the present disclosure, a device emitting signals is denoted a "transmitter" or an "actuator". A device sensing different impinging signals is denoted a "receiver" or a "sensor". A "transducer" is used in the present disclosure as a common term for transmitter, actuator, receiver and sensor.

An embodiment of an arrangement 1 for classifying logs is illustrated in Fig. 1. A log 2 is entered into an introduction part 10 of the arrangement 1 for classifying logs by means of an input conveyor 12. The log 2 is in the present embodiment transported in an axial direction, i.e. in the longitudinal direction of the log 2.

The log 2 is transported through a dimension determining arrangement 16 into an analysis part 20 of the arrangement 1 for classifying logs. The dimension determining arrangement 16 comprises in the present embodiment a laser scanner equipment 18, determining dimension measures of the log 2 such as diameters and length. Based on such measures, a volume of the log 2 can be determined for use in the following quality classification. In the present embodiment, the dimension determining begins when the log comes into contact with a follower wheel 17 of the dimension determining arrangement 16. Four laser sensors 19 measure the circumference shape of the log at equidistant positions along the log 2 as the input conveyor 12 is moving the log 2. The equidistant positions are achieved by controlling the measurement frequency based on the speed of the follower wheel 17. When the back end of the log 2 leaves the follower wheel 17, the follower wheel 17 stops and a total rotation angle of the follower wheel 17 can easily be translated into a length of the log 2. The log length and the diameter or circumference information can easily be transformed into a log volume. This information is later used for classification purposes.

When the log 2 passes the dimension determining arrangement 16 it enters onto a distribution conveyor 22. The distribution conveyor 22 transports the log 2 into an end position, in contact with a stop plate 14, as a preparation for the following entry into an analysis position. A typical time for the log to pass the dimension determining arrangement 16 and reach the stop plate 14 is between 1 and 5 seconds. When analysis is to be performed, the log 2 is forced by side transport means 21 to the side down to a log support structure 24. The log 2 rolls or slides along two input support beams 23 into an analysis position 40, and is kept in the analysis position 40 by the log support structure. A stationary measurement carrier 26 is arranged at the log support structure 24 just in front of the front end of the log 2, i.e., in an axial direction 3 of the log 2. A movable measurement carrier 28 is similarly arranged at the log support structure 24 just behind the back end of the log 2, i.e., also in an axial direction 3 of the log 2. The stationary measurement carrier 26 and the movable measurement carrier 28 are thus placed in positions at both ends of the log 2. The stationary measurement carrier 26 and/ or the movable measurement carrier 28 comprise a respective transducer holder 30. In the present embodiment, each transducer holder 30 comprises a number of transducers 50. These parts will be described more in detail further below.

At the same time as the log 2 is transported to the end position at the distribution conveyor 22, the movable measurement conveyor 28 is moved along a carrier frame 25 into a position just behind the coming position of the back end of the log 2. A position controller 55 is arranged for controlling a coarse position of the movable measurement carrier 28 and is connected to the dimension determining arrangement 16. The position controller 55 comprises a control unit 56 and means 57 for moving the transducers. The position controller 55 is thereby arranged for controlling the coarse position of the movable measurement carrier 28 based on an output from the dimension determining arrangement 16. This is performed at least partly before or at least partly concurrently to the log being brought into the analysis position 40. The coarse position is in this particular embodiment a coarse position of the log support structure 24 in the axial direction as well as in a coarse position of the transducers 50 in a radial direction. When the log is forced into the analysis position, both the stationary measurement carrier 26 and the movable measurement carrier 28 are thus already positioned relatively close to one respective end of the log 2. Fine positioning is then rapidly performed and quality analysis can commence almost immediately, when the log 2 enters into the analysis position 40.

In the analysis position, acoustic measurements are performed on the log. An acoustic measurement equipment comprises the transducers 50 as well as an electronic circuitry 60. The electronic circuitry 60 of the acoustic measurement equipment is connected to the transducers for performing the measurements. Transmitters are instructed to emit acoustical signals causing vibrations propagating in the log 2. In the present embodiment, the transmitters are actuators providing mechanical stress pulses onto the surface of the log end. The acoustic measurement equipment 60 collects relevant information, basically concerning acoustic properties of the log from the sensors. In the present embodiment, the sensors are acoustical sensors placed in mechanical contact with the log 2 in order to register vibrations therein. Some details of the measurements are discussed further below.

Other details are in analogy to the measurement principles presented in WO2007/011296. However, since these details are of minor importance for enabling the advantages achieved with the present invention, further description is omitted.

In the present embodiment, the log support structure 24 further comprises a weighing device 34, comprising a sensor at each end of the log support structure 24, which together determines the total weight of the log 2. Combined with the volume information from the dimension determining arrangement 16, a density of the log 2 can thus be determined, and used for the classification.

Means for classifying 70 the log 2, typically a processor 72, is connected to the acoustic measurement equipment. The processor 72 is in the present embodiment also connected to the dimension determination arrangement 16 for achieving volume information and to the weighing device 34 for achieving weight information. The processor 72 is arranged for classifying the log based on an output from the acoustic measurement equipment, and in the present embodiment also on the volume and weight information. Some details of the classification are discussed further below. Other details are in analogy to the classification principles presented in WO2007/011296. However, since these details are of minor importance for enabling the advantages achieved with the present invention, further description is omitted.

When the classification is performed, the log 2 may in the present embodiment be marked according to the classification. In the present embodiment, a paint sprayer equipment 32 is instructed by the means for classifying 70 to spray paint of a suitable color on the end of the log 2. Such a paint sprayer equipment 32 is as such well known in prior art and is therefore not further discussed. In a simple version, a classification into three classes can be made, where one class corresponds to a white color marking, another class corresponds to a black color marking and a third class corresponds to an unmarked log end. In more elaborate version, different colors and/ or color patterns may be used. The color marking can be used by systems further downstream the process line to distinguish between the different classes.

When analysis and any marking of the log is finished, the log 2 is released from the analysis position by turning down two exit support beams 27 arranged at the log support structure 24. The log 2 is pushed by extractor beams 29 over the exit support beams down to an exit conveyor system (not shown). A total time for entering the analysis position, making the analysis and being released is designed to be in the order of 1 to 3 seconds.

An important part of the present invention is to use the dimension information for a log to enable a pre-setting of the axial position of the movable transducers. Such presetting makes it possible to shorten the time the log spends in analysis position. It is preferable if the entire coarse positioning is performed before or concurrently to the log being brought into the analysis position. However, also a partly performed coarse positioning will reduce the total analysis time.

Dimension determination as such was available already in prior art, e.g., in WO2007/011296. However, the information was collected in order to enable correct analysis of the measurements. This connection is illustrated in Fig. 2. Here, a connection 74 between the dimension determination arrangement 16 and the means for classification 70 illustrates the flow of information. Means for obtaining property parameters 71 provides results to the means for classification over a connection 75, on which results the classification is based. Similarly, weight information and optionally also temperature information and other auxiliary property information are provided by a connection 76 between the weighing device 34, a temperature measuring device 73 and an auxiliary property information device 77 and the means for classification 70. The auxiliary property information device 77 could e.g. be the camera system discussed in connection with Fig. 1OA and 1OB, below. These connections 74, 75, 76 were present also in prior-art classification systems. However, in the present invention, information from the dimension determination arrangement 16 is additionally used for the purpose of speeding up the mechanical operation of the arrangement. To that end, dimension information is sent from the dimension determination arrangement 16 to the position controller 55 by a connection 78. This novel information flow contributes significantly to the advantages described above.

In the embodiment of Fig. 2, it is illustrated that the same dimension determination arrangement 16 provides information both to the position controller 55 and to the means for classification 70. However, anyone skilled in the art realizes that one also could utilize two different dimension determination arrangements 16, one supporting the position controller 55 and the other supporting the means for classification 70.

Fig. 3 illustrates a flow diagram of steps of an embodiment of a method according to the present invention. A method for classifying logs begins in step 200. In step 210, outer dimension of a log is determined. Transducers for acoustic measurements are positioned in step 212 into measuring position at a coming position of the log. The positioning comprises positioning of the transducers at both ends of the coming position of the log in an axial direction of the log. The positioning further comprises actively controlled coarse positioning of the transducers in at least the axial direction based on the determined outer dimensions. The log is brought into an analysis position in step 214. The coarse positioning of step 212 is performed at least partly before or concurrently to the step 214. Acoustic measurements are performed on the log in step 216, whereby the acoustic measurements are performed between the ends of the log. In step 218, the logs are classified, based on the acoustic measurements. The method ends in step 299.

In a basic version according to the present invention, the coarse positioning of the transducers 50 based on dimension information is limited to the axial direction. However, in particular embodiments, also a radial positioning is performed based on dimension information. Fig. 4 is a detailed view of an embodiment of a transducer holder 30 of a movable measuring carrier 28 that can be used in a log classification arrangement, e.g., according to Fig. 1.

A motor 82 is arranged at a frame 80. The shaft of the motor 82 is connected to a gear 84, transferring a rotation of the shaft into a rotation of a trapezoidal screw thread rod 90 extending between the frame 80 and a centre connection box 94, provided in the centre of the frame 80. The trapezoidal screw thread rod 90 is engagably positioned through a threaded hole 92 in a transducer support structure 91. The transducer support structure 91 has two further holes 93, through which a pair of guiding rails are provided. Upon turning the trapezoidal screw thread rod 90, the transducer support structure 91 will move towards the centre connection box 94 or out from the centre connection box 94 depending on the rotation direction. Transducers 50, in this embodiment acoustic or ultrasonic sensors 51, are mounted on the transducer support structure 91. The acoustic or ultrasonic sensors 51 are mounted in a spring-loaded manner in a direction perpendicular to the frame 80 plane. The movable measuring carrier 28 can thereby be moved gently towards an end of a log, and the springs will take care of any deviancies from a perpendicular cut log, whereby the acoustic or ultrasonic sensors 51 are protected from mechanical damage.

From the gear connected directly onto the motor shaft, a motion transfer structure 83 comprises a series of rods 86, gears 84 and edge gears 85 are provided, for transmitting the rotational motion of the motor shaft to three additional sets of trapezoidal screw thread rod 90 and transducer support structures 91. A total of four vibration sensors 51 are thus provided symmetrically around the centre connection box 94, controlled by one common motor 82. The motor is controlled by the position controller 55 (Fig. 1), based on the information from the dimension determination arrangement 16 (Fig. 1). By knowing a diameter of the back end of the log to be classified, the motor 82 can be instructed to move the transducer support structures

91 and thereby the acoustic or ultrasonic sensors 51 to a suitable radial position. In this embodiment, all acoustic or ultrasonic sensors 51 will be situated at the same distance from the centre of the log. Such distance is then adapted to the smallest distance of the log circumference at the back end. Typically a small safety margin will place the vibration sensors safely at the wooden part of the log, but still close to the outer bark layer. Such radial adjustment of the position is according to one embodiment of the present invention performed before or at least concurrently to the log entering the analysis position.

The common operation of the different transducer support structures 91 is enabled due to the adoption of a circular measuring scheme. This is a suitable approach in the embodiment of Fig. 1 , since the angular direction of the log may be altered between the dimension determination and the analysis position. A longest diameter of a non-circular cross-section of an end of the log may be positioned in another direction when the log has entered into the analysis position, which is why angular information can not be used. Furthermore, the analysis of the transit time measurements is simplified by assuming that all transducers are positioned at the same distance from the centre of the log.

The stationary measuring carrier 26 is basically equipped in a corresponding manner. However, here the transducers 50 are instead actuator means capable of introducing acoustic/ elastic waves into the log at different positions. In the embodiment of Fig. 1, one of the transducer support structures 91 of the stationary measuring carrier 26 additionally supports a hammer for exciting vibrations in the other support structures 91 support vibration sensors that measure the resonance frequencies of vibration.

Anyone skilled in the art realizes that the actual number and/ or types of transducers are not of any particular importance for achieving the advantages of the present invention.

If the transport system between the dimension determining arrangement and the analysis position is configured in such a way that angle information can be preserved (an example of which is presented further below), the transducers may be positioned radially independent from each other. Fig. 5 illustrates such a system. Here four motors 82 are provided. Each motor 82 controls the position of a separate transducer 50. In such a configuration, the position controller 55 can instruct each motor 82 separately to position the respective transducer. In such a way, the transducers may e.g. always be positioned at the same distance from the interface between the wood and the bark. However, analysis generally becomes more difficult to perform.

The actual arrangement for moving the transducers can be designed in different ways. Fig. 6 illustrates another embodiment of a transducer holder 30. In this embodiment, the transducer holder 30 comprises a cam disk 100 with four spiral formed slots 108 and a frame disk 102 with four straight radially directed slots 110. The cam disk 100 and the frame disk 102 are mounted concentrically and rotatable with respect to each other. The cam disk 100 is provided with cogs 1 12 at the out rim. Four transducer support structures 91 carry different transducers 50. (Not all of them are marked with reference signs due to readability reasons.) In this particular embodiment, the transducers 50 are four acoustic or ultrasonic sensors 51, three vibration sensors 53 and one actuator 58 for introducing acoustic waves into the log. A guiding pin 106 is mounted in each transducer support structure 91 and passes through a respective slot 108 in the cam disk 100 and a respective slot 110 in the frame disk 102. A motor (not shown) is arranged for rotating the cam disk 100 relative to the frame disk 102. When the cam disk 100 is rotated relative to the frame disk 102, the guiding pins 106 will be forced to move radially with respect to the frame disk 102 and thereby bring the transducers 50 with it. Thus, the motion transfer structure 83 comprises in this embodiment the slots 108, 110 and the guiding pins 106. In such a way, a radial positioning is easily obtained, where all transducers 50 are moved in the same way.

In the embodiments of Figs. 4-6, the radial positioning of the transducers has been performed actively based on input information from the dimension determination arrangement. Such radial positioning is, in analogy with the axial coarse positioning, preferably performed before or concurrently with the entry of the log into analysis position.

In Fig. 7, an embodiment of a transducer holder 30 with a passive radial positioning of the transducers is illustrated. Four transducer support structures 91 carry respective transducers 50. The transducer support structures 91 are attached to interaction structures 120. Each interaction structure 120 has an interaction surface 121 which is inclined with respect to an axial direction. In the present embodiment, the interaction structures 120 are triangular, presenting a straight sloping interaction surface 121. The transducer support structures 91 comprise in this embodiment two holes 126, through which a pair of guiding rails 124 are provided. The guiding rails are rigidly attached in a respective end piece 123 and a common centre piece 122. A spring arrangement 128 provides a small spring force onto each transducer support structure 91, to position the transducer support structure 91 in a pre-determined position if no other forces are present. In the present embodiment, a transducer 50 is also provided at the common centre piece 122 and will therefore always be positioned at the centre of a log 2. This embodiment therefore uses a total of five transducers 50.

A log 2 is entered just in front of the transducer holder 30 of the movable measuring carrier 28 by means of the coarse positioning described further above. The transducer holder 30 is then translated towards the log 2 end, i.e. in an axial direction of the log 2. This translation can be provided by the same means as providing the coarse axial positioning. Alternatively, a separate fine positioning translating means can be provided. The transducer support structures 91 are thereby translated towards the log 2 end. When the interaction surface 121 of the interaction structure 122 comes into contact with the bark at the log 2 end, the transducer support structures 91 are forced outwards in a radial direction. The inclination of the interaction surface 121 is thus arranged for creating a radial, outwards directed, motion of the transducers upon further translation of the transducer holder 30 when the interaction surfaces 121 come into mechanical interaction with the log 2. The axial translation ends when the sensors are positioned at a suitable axial position relative to the log end. If transducers requiring mechanical contact are used, the axial translation ends when the transducers reach the log 2 end. If contact-free transducers are used, a position sensor can be used to end the fine axial positioning at a suitable distance from the log.

Such a final axial position will (ideally) correspond to a predetermined interaction point 129 at the interaction surface 121. Since this interaction point 129 will be supported against the bark of the log 2, the corresponding transducer will be positioned at the same, predetermined, radial distance from a circumference of the log 2 end. A fine axial positioning will preferably take place also at the opposite end of the log 2, whereby the arrangement for classifying logs based on this approach preferably comprises two movable measuring carriers 28.

With a movable measuring carrier 28 being positioned in the above described manner at the ends of a log with uncircular end cross-sections, the transducers will be positioned at different positions relative to the centre of the log. For detailed analysis of the acoustic properties, the analysis algorithms may have to know the actual distances from the centre. The transducer support structures 91 may in such a case be provided with position sensors, being able to detect a distance from the centre of the movable measuring carrier 28. Alternatively, if the transport of the log between the dimension determination arrangement and the analysis position can be performed in a way keeping track on the rotation of the log, the shape information can be extracted from the dimension determination arrangement and transducer positions can be calculated therefrom.

As anyone skilled in the art realizes, a lot of processes have to be performed at or in connection to the analysis position. The time constraints are very demanding in modern saw mills and even fractions of a second will be of importance for the overall capacity. According to the present invention, a major time saving is made by preparing a coarse axial positioning in advance, before the log enters into the analysis position. However, in extremely fast saw mill lines, even such time savings may be insufficient. In such cases, one may have to provide multiple analysis positions. In Fig. 8, another embodiment of an arrangement for classifying logs 1 is illustrated. Here, an analysis position 40 is provided at each side of the input distribution conveyor 22. While analysis of one log 2 at one of the analysis positions 40 is performed, another log 2 may be entered into the other analysis position 40. In such a way, an effective analysis time can be reduced by a factor of two. Since the analysis is believed to be the most crucial part, the provision of multiple analysis positions will be useful to meet an overall throughput rate. Anyone skilled in the art realizes that also more than two analysis positions 40 can be provided, thereby reducing the effective analysis time even further.

In a solution with multiple analysis positions, the log support structures with all its parts, and e.g. the transducers and transducer support structures, have to be provided in multiples. However, with an appropriate design, the dimension determination arrangement, the acoustic measurement equipment 60 and the means for classification 70 can be common resources for both analysis positions 40. In such a way, the provision of double analysis positions will result in limited increased costs compared to a single analysis position configuration.

The actual design of the transport systems in connection with the arrangement for classifying logs are of minor importance for achieving the benefits of the present invention. Many different designs and configurations can be thought of. In the embodiments presented above, axial transport of the logs is used until the analysis position is to be reached, where sideward directed transport principles are utilized. Also solutions where only sideward transports, only axial transports or other combinations of axial and sideward transports are used are possible.

Fig. 9 illustrates yet another embodiment of an arrangement for classifying logs 1. In this embodiment, the log is transported through the dimension determining arrangement 16 onto cradle 130 of conveyor rolls 132. A follower wheel 17 of the dimension determining arrangement 16 is integrated in a last part of the input conveyor 12. The entire cradle 130 is tiltable by means of tiltable supports 131 into an analysis position 40. Weighing devices 34 are integrated in the tiltable supports 131. Fig. 9 illustrates the situation where the cradle is in the analysis position. A movable measuring carrier 28 and a stationary measuring carrier 26 are provided hanging down from a beam 134. The movable measuring carrier 28 is arranged to be movable along the beam to obtain a coarse position. An advantage of such a configuration is that the rotation of the log 2 is fairly well controlled and angular differences in the dimension determination can easily be utilized for analysis purposes. A disadvantage is that the ends of the log 2 have to stick out from the cradle 130 in order to allow the movable measuring carrier 28 to move without collision risks with the cradle 130. This in turn limits the length variations of the logs that can be accepted by the arrangement.

Furthermore, the log 2 has to leave the cradle 130 and the cradle has to be tilted back into a position in front of the dimension determination arrangement 16 before the next log 2 can pass the dimension determination arrangement 16.

Alternative configurations, using e.g. two movable measuring carriers on each side of the log, enable the log to stick out equally on both sides of the cradle. Thereby, the acceptable length variation can be increased. Furthermore, by introducing two cradles being arranged to tilt to analysis positions on both sides of the dimension determination arrangement 16 will also improve the throughput rate. Anyone skilled in the art realizes that the detailed mechanical solutions for transporting the logs to and from the analysis positions can be varied in many different ways.

Fig. 1OA also illustrates an embodiment of an arrangement 1 for classifying logs, here utilizing a transverse transport to and from an analysis position 40. Logs 2 are provided to the introduction part in any conventional manner. The logs 2 are picked out from a pile of logs by a transporting staircase 136 and the transporting staircase 136 together with transport chains 146 convey the logs 8 into the analysis part 20 in a transverse manner up onto a measurement table 135. Upon entering the analysis part 20, a length of the log 2 is measured by a dimension determining arrangement 16, in this embodiment two laser distance meters 140, provided at each ends of the log 2. The length information is as above utilized for an active controlled coarse positioning of transducers 50 in the axial direction 3, described more in detail below. In the present embodiment, the analysis part 20 comprises totally four analysis positions 40 at the measurement table 135, which means that four logs 2 can be analyzed at a time. When the logs 2 enter into the analysis part 20, an Y frame 142 moves up and grips the log 2 from below. The Y frames 142 move with the transport chains 146 and continue the transverse transport of the logs 2. This is illustrated in Fig. 1OA, where the different logs 2 at the measurement table 135 have significantly different lengths and axial positions. At the same time, driving rollers 144 are provided at the Y frames 142, which driving rollers 144 are driven to displace the log 2 in the axial direction 3 towards a stop plate 14. This is performed for four logs 2 at a time, so that all logs 2 are resting against the stop plate 14 in a respective analysis position 40. This results in that one end of the four logs are aligned with each other. Fig. 1OB is a top view of the situation after such an alignment. During this transverse transport and axial alignment, movable measurement carriers 28, on which transducers 50 and in this embodiment also a camera 138 are mounted, are coarse positioned in the vicinity of a respective end of the logs 2, opposite to the aligned ends. The stop plate 14 is moved down so that all the four log ends are free from being covered by any objects. Stationary measurement carriers 26, stationary in the axial direction 3, are moved down to their respective measurement positions. The stationary measurement carriers 26 are in this embodiment also equipped with transducers 50 as well as cameras 138. The stationary measurement carriers 26 and movable measurement carriers 28 are in this embodiment similar to the ones illustrated in Fig. 6.

The cameras 138 are positioned to aim at the respective log end. The cameras are preferably using a preset focus, since the distance to the log ends are fixed within certain uncertainty intervals. The cameras 138 registers pictures of all the log ends, which can be used as additional information during the log classification stage as well as for determine the boundary of the log end, for the fine radial positioning of the transducers 50. This functionality can easily be provided in an embedded image processing computer in each camera. In an alternative embodiment, the cameras 138 may be provided at carriers separate from the measurement carriers 26 and 28. These carriers may both be stationary in the axial direction 3. In such a case, the cameras provided at the aligned log ends can operate with a fixed focus, while the cameras provided for registering the non-aligned ends have to be provided with auto- focus functionalities.

The boundary information obtained from the cameras are preferably used to adjust the radial positions of the transducers 50 at both the stationary measurement carriers 26 and the movable measurement carriers 28. Thereafter, the transducers 50 are fine adjusted in the axial direction 3 into the required measurement positions. In case the transducers 50 operate with measurements or excitations requiring mechanical contact, the transducers are gently moved in contact with the log ends. In case the transducers 50 operate with contact-free measurements or excitations, the transducers are moved into the proper positions at a prerequested distance from the log ends. Acoustic measurements are then performed. After the acoustic measurements, the movable measurement carriers 28 are removed from the log ends in order to allow removal of the logs from the measurement table 135. In the present embodiment, the logs 2 are moved into a discharge transport conveyor 148, which transports the logs away from the arrangement 1 for classifying logs.

Different kinds of information can be extracted from the pictures taken by the cameras. The outer shape can e.g. be analyzed in order to identify occurrence of pressure deformed wood and the pattern and dimensions of the annual rings can give information about expected density of twigs and branches. Such information can be combined with the results of the acoustical measurements for achieving an even more reliable quality classification, c.f. the property measurements 71 in Fig. 2. Such information deduced from the pictures can be extracted from one of the log ends or from both, depending on the allowed complexity and cost of analysis. In order to increase the readability of Figs. 1OA and 1OB, analysis and control electronics are omitted. However, anyone skilled in the art realizes that e.g. different kinds of electronic circuitry for position control, classifying, acoustical measurement control, and camera control has to be provided.

In an alternative embodiment, the Y frames 142 may lack driving rollers 144. In such an embodiment, the Y frames 142 just lift the logs from the measurement table 135 to fix them in position. Instead, movable measurement carriers 28 are provided at both ends of the log 2. The coarse positioning there preferably involves coarse positioning of the movable measurement carriers 28 on both ends of the log 2. Since the actual longitudinal position of the log on the measurement table 135 may shift somewhat during the transverse transport, a coarse positioning in longitudinal direction has preferably to be performed with sufficient security margins, and a fine positioning can be further supported by camera picture analysis and/ or laser distance measurements at each analysis position.

In many saw mills of today, different dimension determination arrangements are already available. These arrangements are, however, typically connected to a section where the logs are sorted according to diameter in different bins. One problem of prior art diameter sorting arrangements is that the diameter determination easily can be disturbed by e.g. branches, chips or damages at the logs. There is then a risk that the logs are sorted into the wrong bin. In many cases are the equipments following such diameter sorting adapted to a narrow diameter range and logs falling outside that range may disturb the following processes. Arrangements for correcting the sorting or manual interference with the process are cumbersome and are generally expensive. Today, it is not uncommon that up to 5% of all logs are sorted into the wrong bin. An approach to achieving an improved fractioning of logs according to diameter would therefore be appreciated. When introducing a log classification arrangement according to the present invention, a redundant source of dimension information becomes available. In a typical process line, a log classification section is typically inserted before any sorting according to diameter. By using the available redundant dimension information, erroneous diameter determinations may be discovered.

Fig. 1 1 illustrates a block diagram over such an arrangement. A saw mill production line 150 comprises a log classification section 152 having an arrangement for log classification 152 according to the above described principles. Logs pass through the log classification section 152, have their dimensions measured by a dimension determining arrangement 16 and can thus easily be associated with the corresponding diameter data 160. When exiting the log classification section 152, the logs are transported into a diameter sorting section 154. In the diameter sorting section 154, an additional diameter measuring equipment 156 measures the diameter of the incoming logs. These measurements together with the information 160 provided from the log classification section 152 are input into a control unit 164. The control unit 164 assigns a diameter class to each log. When the logs are output into a diameter sorting arrangement 166, the logs are directed into different bins 158 depending on the diameter class. In the control unit 164 independent diameter measurements are available and there is thus an opportunity to find discrepancies between the two independent diameter determinations. A part of such discrepancies can be explained by systematic measurement differences and may easily be calibrated by statistical methods. If such calibrated diameter measures anyway differ between the two measurements more than a predetermined threshold, one may assume that at least one of the measurements have to be erroneous. The log can then be assigned to be separated into a remeasuring line 162 and be transported back to the log classification section 152 instead of being separated into a bin 158 of a particular diameter range. Such simple arrangement is believed to be capable of increasing the probability of correct sorting, possibly up to a degree of 99%. The cost reduction for correcting mis- sorted logs will be enormous.

In an alternative embodiment, the diameter data 160 can be accompanied by data associated with the classification of the log, performed in the log classification section 152. The control unit 164 can then be arranged to assign a classification, not only based on log diameter, but also on various property classification. This makes it possible e.g. to separate logs being classified as low quality logs into particular bins, irrespective of the diameter, while logs of "normal" quality still is sorted by diameter. Also exceptionally high-quality logs may be separated out in particular bins.

One alternative to the remeasuring line 162 would be to provide the control unit 164 with a discrepancy analysis section, provided with software for evaluating situations where the dimension measures differ, and provide a best estimate of a probable diameter, which then is used for sorting purposes.

In the above description, the embodiments are described in detail. There are, however, many variants and modifications that also will operate well.

A laser scanner equipment is used as an example of a dimension determination arrangement, where a follower wheel is responsible for the actual length measurement. First of all, other length measuring devices and arrangements can be used. A light emitter and optical sensor arranged at opposite sides of the log path will easily detect the beginning and end of a log. Together with speed information from the conveyor equipment, a log length can easily be determined. Likewise, dimension determination arrangements based on e.g. other type of radiation can equally well be utilized. Also pure mechanical solutions can be found, e.g., where a number of follower wheels are provided around the periphery of the log to determine diameter as well as length. Depending on the analysis method used, different kinds of transducers can be provided. In a preferred embodiment, analysis according to the principles presented in WO2007/011296 is applied. Sensors and actuators for both transit time measurements and resonance measurements are then provided at the ends of the log. Today, vibration sensors being in contact with the wooden surface are a good choice, e.g. different kinds of accelerometers. The acoustic transmitters may be actuators providing a mechanical interaction with the log. Different kinds of transducers used in prior art can thereby be used to optimize the measurements of the properties that are believed to be most significant for quality classification. In a near future, it is believed that transducers based on contact- free excitation and/ or sensing of vibrations in the log are available for use in industrial applications.

The number of transducers on each side of the log also depends on the actual analysis that is going to be performed. In order to enable analysis according to the principles presented in WO2007/011296, at least two transducers are provided at each side. As can see in the embodiments described above, more transducers are also possible.

It is also possible to attach more than one transducer to each transducer support structure. In that way, less mechanical transfer mechanisms have to be provided. However, the positions of the transducers can not be controlled individually.

In the embodiment of Fig. 1, it is described that the classification marking is performed when the log still remains in the analysis position. In order to shorten the time in the analysis position even further, such marking can be made in a later stage. In such a configuration, the identities of the logs have to be possible to recover, which easily is provided by maintaining the order of the logs in which they were analyzed.

In the embodiments described above, the acoustic measurement equipment, the means for classifying, the control unit of the position control and the dimension determination arrangement are described as separate units. However, at least parts of these items are advantageously implemented by different processors and functionality of two or more of the items may therefore advantageously be combined in one and the same processor. The separate units illustrated in the figures above should therefore be considered as functionality units rather than physical unit. However, different physical units are of course also possible to use.

The embodiments described above are thus to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

1. Method for classifying logs, comprising the steps of: determining (210) outer dimensions of a log (2); bringing (214) said log into an analysis position (40); positioning (212) transducers (50) for acoustic measurements into measuring position at said log (2); said step of positioning (212) comprises positioning said transducers (50) at both ends of said log (2) in an axial direction of said log (2); performing (216) acoustic measurements on said log (2); said step of performing (216) acoustic measurements comprises performing acoustic measurements between said ends of said log (2); and classifying (218) said log (2) based on said acoustic measurements, characterized in that said step of positioning (212) further comprises actively controlled coarse positioning of said transducers (50) in said axial direction based on said determined outer dimensions; said coarse positioning being performed at least partly before or concurrently to said step of bringing (214) said log (2) into said analysis position (40).

2. Method according to claim 1, characterized in that said step of determining (210) comprises laser scanning of said log (2) .

3. Method according to claim 1 or 2, characterized in that said step of positioning (212) further comprises: moving transducer support structures (91) to which said transducers (50) are attached in said axial direction; creating a radial, outwards directed, motion of said transducers (50) when said transducer support structures (91) come in contact with said log

(2) by an mechanical interaction between an interaction surface (121), inclined with respect to said axial direction, of said transducer support structures (91) and said log (2), whereby said transducers (50) becomes positioned at predetermined radial distances from an circumference of a log (2) end.

4. Method according to claim 1 or 2, characterized in that said step of positioning (212) further comprises actively controlled positioning of said transducers (50) in radial direction, with respect to said log (2), based on said determined outer dimensions, whereby said transducers (50) becomes positioned at predetermined radial distances from an circumference of a log (2) end.

5. Method according to claim 1 or 2, characterized by the further step of: registering a boundary shape of each log end; said step of positioning (212) further comprising actively controlled positioning of said transducers (50) in radial direction, with respect to said log (2), based on said registered boundary shapes, whereby said transducers

(50) becomes positioned at predetermined radial distances from an circumference of a log (2) end.

6. Method according to claim 5, characterized in that said registering a boundary shape of each log is performed by registering a respective picture of the log ends, and in that said classifying (218) of said log (2) is further based on log properties extracted from said respective pictures.

7. Method according to any of the claims 4 to 6, characterized in that said actively controlled positioning in radial direction is performed by a common motor via motion transfer structures (83) .

8. Method according to any of the claims 4 to 6, characterized in that said actively controlled positioning in radial direction is performed by a separate motor for each transducer (50) .

9. Method according to any of the claims 1 to 8, characterized in that at least one of said transducer support structures (91) is attached to more than one transducer (50).

10. Method according to any of the claims 1 to 9, characterized in that said transducers (50) are selected from the group of acoustic sensor and acoustic transmitter.

1 1. Method according to any of the claims 1 to 10, characterized in that said transducers (50) are at least two at each side of said log (2) .

12. Method according to claim 1 1, characterized in that said transducers (50) are at least four at each side of said log (2).

13. Arrangement (1) for classifying logs, comprising: log support structure (24) for holding a log (2) in an analysis position (40); transport means (21) for bringing said log (2) into said analysis position (40); dimension determining arrangement (16), arranged for determining outer dimensions of said log (2) before said log (2) is brought into said analysis position (40); transducers (50) of an acoustic measurement equipment for acoustic measurements attached to transducer support structures (91) and positionable into measuring positions at said log (2); said transducers (50) are arranged to be positionable into measuring positions at both ends of said log (2) in an axial direction of said log (2); and electronic circuitry (60) of said acoustic measurement equipment connected to said transducers (50) for performing acoustic measurements on said log (2); said electronic circuitry (60) of said acoustic measurement equipment is arranged for performing acoustic measurements between said ends of said log (2); and means for classifying (70) said log (2), connected to said electronic circuitry (60) of said acoustic measurement equipment, said means for classifying (70) being arranged for classifying said log (2) based on an output from said electronic circuitry (60) of said acoustic measurement equipment, characterized by position control (55), connected to said dimension determining arrangement (16), and arranged for controlling a coarse position in said axial direction of said transducer support structures (91); said position control (55) being arranged for controlling said coarse position in said axial direction based on an output from said dimension determining arrangement (16); said position control (55) being further arranged for performing said controlling at least partly before or at least partly concurrently to said log (2) being brought into said analysis position (40) .

14. Arrangement according to claim 13, characterized in that dimension determining arrangement (16) comprises a laser scanner equipment (18).

15. Arrangement according to claim 13 or 14, characterized in that said transducer support structures (91) have interaction surfaces

(121), inclined with respect to said axial direction; and by means for translating said transducer support structures (91) in said axial direction; said transducer support structures (91) being arranged for creating a radial, outwards directed, motion of said transducers (50) upon further translation of said transducer support structure (91) when said interaction surfaces (121) come into mechanical interaction with said log (2); whereby said transducers (50) become positioned at predetermined radial distances from an circumference of a log (2) end.

16. Arrangement according to claim 15, characterized in that said transducer support structure (91) presents a triangular shape in an axial direction of the log (2) .

17. Arrangement according to claim 16, characterized by a spring arrangement (128) providing a spring force on said transducer support structure (91) towards a centre of a log cross-section.

18. Arrangement according to claim 13 or 14, characterized in that said position control (55) is further arranged for actively controlling positioning of said transducers (50) at predetermined radial distances from an circumference of a log (2) end, based on said determined outer dimensions.

19. Arrangment according to claim 13 or 14, characterized by a camera arranged for registering a boundary shape of each log end; said position control (55) being further arranged for actively controlling positioning of said transducers (50) at predetermined radial distances from an circumference of a log (2) end, based on said boundary shape.

20. Method according to claim 19, characterized in that said camera is arranged for registering a respective picture of the log ends, and in that said means for classifying (70) said log (2) being arranged for classifying said log

(2) further based on log properties extracted from said respective pictures.

21. Arrangement according to any of the claims 18 to 20, characterized in that said transducer support structures (91) are arranged to be guided along predetermined paths in radial direction and said position control (55) is arranged for moving said transducer support structures (91).

22. Arrangement according to claim 21, characterized in that said position control (55) comprises a common motor (82) and motion transfer structures (83) on each side of the log (2), arranged for moving said transducer support structures (91).

23. Arrangement according to claim 21, characterized in that said position control (55) comprises a separate motor (82) for moving each transducer support structure (91) independently.

24. Arrangement according to any of the claims 13 to 23, characterized in that at least one of said transducer support structures (91) is attached to more than one transducer (50).

25. Arrangement according to any of the claims 13 to 24, characterized in that said transducers are selected from the group of acoustic sensor and acoustic transmitter.

26. Arrangement according to any of the claims 13 to 25, characterized in that said transducers are at least two at each side of said log.

27. Arrangement according to claim 26, characterized in that said transducers are at least four at each side of said log.