The present invention concerns a method for peeling veneer from a log. The method in accordance with the invention comprises operations that enable an automatic calibration of the apparatus used for the centring operation upstream of the peeling.

In conventional veneer peeling, the centring of the log to be taken to the peeling is performed in a device located immediately upstream of the lathe. In this centring device an optimal spinning axis is tried to be determined, around which the log to be rotated in the lathe can be peeled so as to gain an appropriate veneer yield. A traditional object has been to determine by the centring device a maximal cylinder in the log, the centre axis thereof being located as the rotation centre, after the log has been moved to the rotating spindles of the veneer peeling lathe.

For ensuring the appropriate operation of the centring device, it must be calibrated in several situations of operation. These situations include for instance introduction of a new centring device or the centring device after maintenance, elimination of the changes caused by wearing, as well as change of sensors and measuring elements used for the centring operation or the supervision thereof. Also changes in the operation of the devices during the use should be taken into account in order to receive an accurate centring result. The measuring sensors are affected by thermal drift and mechanical components are subject to wearing and temperature changes affecting the accuracy of operation of the components.

A method being basically reliable and generally used for calibrating the centring device is performed so that a log is first peeled perfectly round in the lathe. This round log is then returned to the centring device and the log is measured and centred with the device. Based on the measuring results, a new calibrated parameters will be determined for the centring device. For verifying the parameters, the log is positioned based on the centring data to the spindles of the lathe, and, in general, the received centring result will be checked by peeling the log into veneer and observing, how coherent the achieved veneer web is. The centring result can also be defined e. g. by means of devices located in connection with the lathe, said devices being used for determining the distance of the surface of the log from the measuring point. These measurements are performed at two points of the log length, usually

near the ends of the log. For finding the reason for an eventual eccentricity discovered in the lathe, the centring operation and its verification must be performed several times. In any case the calibration of the centring device causes a significant interruption of the production. hi the method in accordance with the present invention, the calibration of the centring device can be performed under normal operation of the centring device and the lathe, and no special interruptions of operation are needed for performing the calibration.

The substantial characteristics of the invention will become apparent from the enclosed claim 1.

When implementing the invention, the peeling can be performed either as an actual peeling, the result of which will be controlled, or as simulated peeling using the same values as the actual peeling. The simulated peeling gives a result corresponding the result given by the actual peeling when the centring device operates correctly. Deviations discovered in the peeling results indicate failed operations of the centring device. These discovered deviation are utilized and the X and/or Y direction are corrected in the centring device so, that the deviations are eliminated. The implementation of the method requires that the equipment includes devices for computerized processing, in general a suitable computer, and appropriate measuring devices for verifying the peeling result. Modern peeling lathe lines already include verifying devices of peeling yield, usable for implementing the invention. Also devices usable for computerized processing of data can be included in the peeling lathe lines in use.

When operating in accordance with an alternative embodiment of the invention, a log being determined by its contour in a centring device is positioned to the spindles in accordance with the positioning parameters given by the centring device. After this, the contour of the log is once more determined, positioned to the spindles of the lathe during the peeling revolutions, and an eventual deviation from the optimal rotation centre is defined based on this determination. The operation of the centring device is calibrated based on the data received from this latter determination.

The invention will be described by means of the enclosed drawing, as an example only, wherein Figure 1 shows one embodiment of a peeling lathe line, wherein the calibrations of the both embodiments of the centring device are applicable, and Figure 2 shows another embodiment of the peeling lathe line, providing the calibration of a centring device in accordance with one embodiment of the invention.

In figure 1 a peeling lathe line is shown, wherein the devices include a centring device of a log 1 going to be peeled, waiting station of a centred log 5, and a peeling station with a log 6 placed therein. The log 1 located in the centring position is supported by the rotating spindles 4 of the station, by means of which the log is rotated about its longitudinal axis. For scanning the distance of the surface during the measurement rotation, the centring device comprises sensors 2, that can be for instance laser distance scanning sensors. There are sensors located at determined distances along the length of the log. The data given by the sensors 2 is transmitted to the computer 8 of the centring device, which determines the contour of the log based on this data. Based on this contour, as well as on the objectives set for the peeling, a rotation axis is determined for the log by the computer 8, according to which the log must be positioned to the spindles 7 of the lathe for achieving the required result. The centring device can also be implemented in a way known in the art, in which the log can be placed immovably in the spindles of the centring device, and the contour is determined by scanning the surface of the log from several directions.

In the described embodiment, there is provided a distance sensor 12 in connection with the lathe, said distance sensors being applicable to the corresponding operation as the sensors 2 used in connection with the centring device. With these sensors 12 it is possible to measure during the peeling revolutions, that the log was positioned to the position in the spindles of the lathe corresponding to the rotation centre defined by the XY centring device. There can be a plurality of these sensors, as shown in the figure, or only two, preferably in the vicinity of the ends of the log.

The data from the sensors 12 is transmitted to the data processing device, mainly to the computer 13. This computer has data communication with the computer 8 of the centring device. With the computer 8 and/or 13 also the computerized virtual peeling is performed, based on the data received from the sensors 2 and the set values of the lathe. The result of the actual peeling operation given by the sensors 12 is compared with the computerized peeling, and in case any deviations are discovered, the reason for the deviations will be determined with the computer 8 and/or 13, and calibration commands are given to the centring device in order to eliminate the deviations.

In equipment in accordance with figure 2, the peeling result is controlled by means of a control apparatus 10 arranged in connection with the clipper 11, said control apparatus being for instance an optical camera device. The data received from the camera device is input to the computer 14 controlling the operation of the clipper, said computer being in operation contact with the computer 13. The centring device calculates the configuration of the veneer web based on the centring and other data, and this is compared with the actual veneer web. The actual veneer web is received from the camera of the clipper. Other data, like the adjusted thickness of the veneer, can be received for instance from the control of the clipper. Eventual faulty centring of the XY-centring device is calculated based on the results of the comparison.

The data to be used for the calibration of the centring device is preferably collected from several peeling events, in practice from several successive peelings of logs for providing a reliable calculated calibration result. An advantageous embodiment is to collect peeling result data continuously in connection with each peeling event and to analyze the results from the material received from few tens, for instance about 30 successive measurements, and to perform the calibration of the XY positioning based on the results of this sequence. The material formed by this amount of events provides a calculated possibility to evaluate the size and direction of the correction of the XY centring.