The present invention relates to a procedure and an appara¬ tus for the determination of the ending instant of the block rounding stage in a veneer-cutting machine.

At present, the ending of the rounding stage is practically based on block diameter data as measured by visual estima¬ tion, by means of a camera or in the centring device. The methods currently used have several drawbacks. Manual ending of the rounding stage on the basis of visual obser¬ vation requires continuous attention. Moreover, modern machines use higher speeds of rotation as well as greater barking depths, making visual estimation more difficult.

When the sheet of wood produced by the rounding operation is observed using a camera (e.g. a line camera) placed after the tool carriage, the line of observation is, due to the mechanical dimensions, separated from the line of the cutting tool by a distance of about 1 - 1.5 m. There is a corresponding lag in the data concerning the phase of the rounding operation. As the operation of line camera control is based on the distinction and comparison of shades of gray, the colour differences in the veneer, caused by the wood material itself and by moisture variations, result in evaluation errors. Another source of evaluation errors is the sensitivity of the line camera to changes in illumina¬ tion (condition and soiling of the lamps, wrong direction of light, external lights and shades, e.g. sunlight).

When the ending instant of the rounding stage is based on block diameter data measured in the centring device, in which case the measurement can be performed using a line camera, matrix camera, laser distance measurement, ultra¬ sonic measurement or mechanical measurement, the mechanical

transfer errors occurring in the centring of the block and those occurring during the positioning of the block between the mandrels cause errors and inaccuracies in the determi¬ nation of the ending instant of the block rounding stage. Furthermore, the number of measuring points in the trans¬ verse and longitudinal sections is limited, which means that the ending of the rounding stage is based on defective data.

FI publication 73908 proposes a procedure for the control of the debarking and rounding of a block of wood in a veneer-cutting machine whereby the quality of the surface of the rotating block is observed by directing a beam of light at the block in its longitudinal direction and detecting the radiation reflected from the block by means of a semiconductor camera. However, due to the mechanical structures, the point under observation lags behind the cutting line by about 3/4 of a turn of the block, involving a corrseponding time lag in the data regarding the phase of the rounding operation. The interpretation is based on the greyness difference between the uncut block surface and the surface after the cutting, for which reason colour differ¬ ences in the wood material itself cause errors in the in¬ terpretation of the data. Due to the facts mentioned above, this procedure is sensitive to changes in illumination in the same way as when the wood sheet produced by the block rounding operation is observed by means a line camera as mentioned above.

The object of the present invention is to eliminate the drawbacks presented above. The procedure of the invention for determining the ending instant of the block rounding stage in a veneer-cutting machine is characterized in that the sound produced by the cutting during the rounding stage is monitored by means of one or more sensors and the signal obtained from said sensors is passed to a data processing unit which, based on the cutting sound, determines the

instant at which the rounding stage is to be ended and starts certain actions known in themselves for ending the rounding stage.

The preferred embodiments of the invention are presented in the other claims.

As compared to previously known systems, the invention provides the following advantages: The data on the cutting sound is real-time data, providing real information on the phase of the rounding operation. The data being processed is not affected by measuring, centring or transfer errors or colour differences. The measured data indicates the cutting width of the cutting tool as continuous data in relation to the block length. The procedure is applicable to all existing lathe types regardless of the peripherals they use, e.g. the centring device. Moreover, the costs of the procedure as compared to other systems are reasonable.

In the following, the invention is described in detail by the aid of examples by referring to the attached drawing, in which

Fig. 1 presents a veneer-cutting machine in lateral view.

Fig. 2 presents a veneer-cutting machine in top view.

Fig. 1 shows an end frame 1 and the tool carriage 2 of a veneer-cutting machine, the tool carriage being provided with a cutting tool 3 and a counter blade 4. The position of the tool carriage is monitored by means of a position sensor 5, e.g. a potentiometer. The veneer sheet 8 cut from the block 7 rotating between the mandrels 6 comes out from the machine through the gap between the cutting tool and the counter blade. Fig. 2 shows a top view of the tool carriage 2, lathe end frames 1 and the block 7 rotating between the mandrels 6. Moreover, Fig. 2 shows the main

motor 9 together with a current measuring unit 10 and a tachometer generator for measuring the speed of rotation of the mandrels.

In the procedure of the invention, the determination of the end of the block rounding stage is based on the monitoring and processing of the sound produced by the cutting action. The rounding stage is followed by the main cutting opera¬ tion in which a veneer sheet for practical utilization is produced.

The cutting sound is monitored by means of one or more sen¬ sors 12 of a suitable type (microphones), placed e.g. near the tool carriage, on one side of it. The cutting sound signals obtained from the sensors are passed to a micropro¬ cessor 13 which processes them, performs calculations and draws conclusions. The rounding stage can be ended e.g. on the basis of the intensity of the cutting sound. To end the rounding stage, the microprocessor 13 gives an end signal to the lathe control centre, whereupon the actions required for the ending, known in themselves, are started.

The number of sensors used depends on the length of the block and the accuracy aimed at. The sensors may be placed on different sides of the veneer-cutting machine, depending on the mechanical structures. In practice the sensors are so located that they will easily perceive the sound and that they are mechanically protected. The sensor action may be based on the propagation of sound in air, metal or some other medium suited for the purpose. In Figs. 1 and 2, the sensors 12 are located behind the tool carriage 2.

In addition to the data obtained from the sensors measuring the cutting sound, the procedure makes use of the mandrel r.p.m. data in the inference process. Additional auxiliary data may be obtained by monitoring the tool carriage posi¬ tion and the main motor load. The monitoring is continuous,

and the monitoring cycle is one mandrel revolution (block revolution) . The beginning of the monitoring cycle is varied depending on the incoming sound signal.

Besides the cutting sound, it is possible to monitor and analyze the power or current consumed by the mandrel actua¬ tor, or some other quantity proportional to the load. If necessary, the system may also provide production report data (e.g. net raw material in m ³ , average block diameters etc. ) .

It is obvious to a person skilled in the art that different embodiments of the invention are not restricted to the examples presented above, but that they may be varied within the scope of the following claims.