FI113496B - Method for identifying stones from a stream of wood - Google Patents

Description

113496

METHOD FOR IDENTIFYING STONE FROM A WOOD FLOW

The field of application of the invented method is mainly in the wood processing industry, where the raw wood stream 5 sometimes also comes with stones. Stones often cause severe damage in the early stages of wood treatment, such as debarking, chipping and sawing. This method has been developed to identify these stones from the wood stream. Some methods utilizing X-ray imaging have been developed. Methods are expensive and often too slow to accurately capture fast and wide (often 1-3 m / s) tree streams. The imaging element should be at least 2.5 cm x 2.5 cm in order to avoid major blade damage, for example in mass-industry hackers. 15 So the minimum frame rate is about 2000 shots per second (then the conveyor belt is 1.2 m wide and advances at 1 m / s). However, a single shooting direction is not sufficient to detect a rock, as a similar branch can be caused by a branch in the appropriate direction. Often, even the shots will leave an edge ... 20 areas in some kind of shadow.

[The object of the invention is achieved by a method characterized by what is claimed.

The method according to the invention provides a measurement of the · ·. * Wood current from two different directions (often almost perpendicular directions), which produces a 3D effect and a long ... branch cannot, for example, produce gamma rays anymore ... · In both measurements, could be interpreted as a stone and stop the process of finding and removing a stone. The method can also use two different detectors to measure X-ray or gamma-ray intensities, eliminating blind spots that are easily trapped at the edges of the wood conveyor, even in confined 11349f 2 geometries. The most preferred type of penetrating radiation, especially for thick supports, is Co-60 gamma radiation. Fast-moving radiation sources, on the other hand, avoid the use of expensive vector detectors that would otherwise be needed to provide transverse resolution.

Fig. 1A is a plan view of the apparatus 10 according to the method, and Fig. 1B is a side elevational view of a log conveyor in which the log conveyor runs in its longitudinal direction.

The operation of the invented method 15 with the aid of the drawings will now be explained. The conveyor belt (9) passes through the measuring device, carrying trees (10) and possible stones (11). The device is constructed according to the method so that radiation sources (1) and (2) move rapidly under the conveyor belt (9). The radiation detector (8) 20 detects radiation from one radiation source (1) at a time while another radiation source (2) is returning to the other edge, radiation-shielded (4) down the tunnel. The operation of the method is as follows: Trees (10) and possible stones (9) '· passing through the conveyor belt (9) in Figure 1A to the left ··· 1 25 to the right and the detector (8) detecting a rapid absorption pit, recording and waiting for a certain time calculated on the belt (9) speed, taking into account any · ... · geometry, if in a given time in the second half ... · absorption of the radiation source must be fast well in this case, an alarm 30 and a stone searched and removed.

There may also be two detectors which, as shown in Figure IA, are at the edge of the conveyor belt (dashed line), • 1 »this eliminates the need to position the radiation source path 3 113496 due to geometry well over the edges of the conveyor belt (9) 1) and (2) move by means of shafts (5) and sprockets (6) as the motor (7) rotates 5. The chains (3) may be, for example, metal chains or toothed belts, but they must travel synchronously.

The invention is not limited to the embodiment shown, but may be modified within the scope of the claims. 1 · ·

Claims (3)

A method for detecting rocks from a wood stream based on electromagnetic radiation absorption measurement, comprising one or more detectors (8) for measuring intensity of radiation on one side of the transport space of a tree, which see signals emitted by radiation sources (1) and (2) that only one radiation (1) from each of two or more sources is emitted by the detector (8), characterized in that the radiation emitted to the detector (8) by the transmitting radiation transverse to the direction of transport of the wood, 10 spaced apart, wells, and that an alarm will be given to identify the stone when the absorption measurement emitted by the other radiation source (2) will also be accompanied by a suspected absorption well caused by the rock within the time that the calculated geometry is calculated. which measures the absorption of wood from different directions, and the velocity of the wood and possible stones. 1 1349ί Method according to Claim 1, characterized in that the radiation detectors (8) (2) are located at the edges of the conveyor (9) or the transport space. 20, and the processing of the signals emitted by the detectors in the analysis to identify the stone is each similar to that described in claim 1. Method according to claims 1 and 2, characterized in that electromagnetic X-ray or gamma radiation is used as radiation sources. * 5 1 1349f