FI98098C - Apparatus for examining non-metallic measuring objects - Google Patents

Description

98098

Apparatus for testing non-metallic measuring objects Anordning för undersökning av icke-metalliska mätföremäl

The invention relates to an apparatus for examining non-metallic objects (hereinafter "measuring objects"), wherein "examination" means determining the presence of an element, e.g. rot, branches or foreign objects, in particular its location when the density of the element deviates from the normal or of an average density of 10. The invention is suitable for use primarily in the wood industry for examining logs ("log tomography"), or for examining, but not limited to, structural elements of a particular composite material such as wood chips and glue.

15

It has already been proposed that for this purpose a flat beam from a gamma radiation source is transmitted through the body, and on the opposite side the attenuating radiation flux is received in an arcuate configuration of separate detectors, whereby the detector signals are evaluated in computer hardware. The radiation source and detector assembly are rotated around the body, or vice versa, to locate any defects found.

In another rotatable device 25 proposed for the same purpose, the radiation source is an X-ray tube.

The required rotation mechanism makes the structure more expensive, and in addition, in the sawmill environment, the aim is to avoid moving parts of the measuring equipment as much as possible.

30

In another device known for the same purpose, the gamma radiation sources and detector assemblies are fixedly arranged, and the gamma radiation sources comprise a scanning device for causing a narrow beam to perform a scanning motion comprising the entire detector, which in this case need not comprise a sweeping motion. comprises a set of separate elements because the signal's own timing information can be utilized.

Canadian patent application 575,481 (corresponding to 5 Swedish patent applications 8902791-6) for the same purpose discloses a method and apparatus in which three radiation sources emitting electromagnetic energy capable of transmitting a log under investigation are fixedly arranged at angular distances of 120 ° at longitudinal distances. Opposite each radiation source on the opposite side of the log diagonal is a fixed, radiation-sensitive receiver member consisting of a linear detector assembly, i.e. a plurality of detectors spaced at selected mutual distances (in the shape of a circular arc 15) at a selected radius. Each detector assembly receives radiation from a single radiation source.

The measuring object passes on a longitudinal conveyor through the measuring station, and the output signals of the detectors are evaluated in computer hardware programmed so that from said output signals the presence and location of elements of different density (e.g. internal defects, e.g. rot or foreign objects, e.g. nails) can be determined. .

25

For another purpose, namely to measure the diameter of a log, Swedish patent 425 126 (corresponding to U.S. patent 4,555,633) proposes that radiation be provided on two opposite sides of the measuring object, e.g.

30 mixed rows of transmitters and receivers of visible light impermeable to 30 measuring objects, whereby the number of receivers is smaller than the number of transmitters. In computer hardware, the diameter is determined from which radiation paths between the transmitters and receivers are covered by the measured object.

35 3 98098

It is an object of the present invention to provide a device with no. has no moving parts, and provides more accurate positioning information, allowing the relatively expensive 5 different detectors of the detector assembly to be used more efficiently, namely multiple times.

The invention is characterized by the features set forth in the appended claims. Unlike the above-mentioned diameter measuring devices 10, on the one side of the measuring object according to the present invention there is a row with only transmitters and on the other side a row with only receivers, the number of receivers being larger than the transmitters, and the radiation is permeable to the measuring object. species.

Because detectors in the same detector configuration consume radiation from different perspectives in succession (i.e., from multiple spaced radiation sources, preferably more than two), positioning becomes better, even to the extent that a sufficiently large number of spaced apart sources can provide a single replace, for example, the three pairs of measurements in the aforementioned Canadian patent application.

25

The invention will now be described in more detail with the aid of the accompanying schematic drawings, in which Figure 1 shows a first embodiment of the device according to the invention and Figure 2 a second embodiment, and in which Figure 3 shows a third alternative on a smaller scale.

• According to Figure 1, the measuring object formed by the log 50 is examined.

The logs 50 are conveyed by a longitudinal conveyor (keratin track) 51 perpendicular to the plane of the drawing through a device 35 according to the invention comprising a single fixed transmitter assembly 10 'comprising seven or adjacent radiating sources 10 in selected rows. 'a, 10'e, 10'g, and a single, also fixed, detector assembly, i.e. a receiver element 30', comprising 5 detectors (e.g. several hundred) arranged in a row next to each other, arranged at selected mutual distances d, of a separate type known per se, such as 30'a.

Radiation sources 10'a, etc. emit radiation that passes through 10 measurement objects, and detectors 30'a, etc. are sensitive to this radiation. The configuration of the radiation sources 10 'and the configuration of the detectors 30' together form a measuring pair having a main measuring direction m (the measuring direction can be defined as normal in the detector row).

15

Each radiation source 10'a, etc., emits an expanding control beam bounded by boundary beams, such as 10'a ', 10'a ", and impinges on the entire opposite receiver member 30'. As an exception to the above devices for locating elements 20 of different densities, the present The measuring pair of the device according to the present invention has a plurality of radiation sources directed towards the same configuration of separate detectors.

However, before the radiation reaches the detectors, it generally first passes through the log 50, as seen, for example, with beams 10'a "and 20'e", whereby the measuring object 50 attenuates it. Attenuation then occurs to varying degrees, partly due to the different lengths of the different radiation paths in the measuring object, and partly due to the presence or absence of possible defects 30 and their quality.

The separate radiation sources 10'a of the transmitter assembly 10 'are activated from the computer unit or hardware 52 in succession for a period of the order of a few milliseconds.

A shutter individually controllable by a computer unit 52, such as 5 98098 11'a, 11'f, is provided in front of each radiation source 10'a; for the sake of clarity, only the connection of the shutter 11'f is shown in the drawing.

Activation refers to the state in which the radiation from the 5 radiation sources reaches the measuring object. This can be, as in the present example, the removal of the protection of the continuously radiating radiation source, or the ignition of an otherwise extinguished radiation source.

In the present example, it is assumed that the radiation is isotopic radiation, that the radiation sources 10'a, etc. are formed e.g.

192 137

Ir or Cs radiation sources, and that a configuration of scintillation detectors is used as the receiver member 30 '. Activation is achieved by successively opening the shutters 11'a, etc., so that they are then closed again.

However, the shutters can be omitted when using radiation sources, such as, for example, X-ray tubes, in which activation and deactivation can be achieved by switching the supply current on and off by the computer device 20, as shown in Fig. 1 by the dashed line connection r.

X-ray receiver elements comprising 512 or 1024 separate detector elements at a 0.45 mm pixel distance are marketed, for example, by Thomson Tubes Electroniques, Boulogne-Billancourt, under the designation THX 2024.

The separate detectors of the receiver element produce output signals, the magnitude of which depends not only on the performance of the respective radiation source 30 but also on the amount of attenuation, and which are input to the computer unit 52 for evaluation. included within the scope of the present invention; such a method is disclosed, for example, in the Canadian and Swedish patent applications mentioned in introduction 98098 6, respectively.

According to Figure 2, the device has a first transmitter assembly 5 comprising three in-line or adjacent radiation sources, i.e. transmitter 10a, 10b, 10c, and a second transmitter assembly 20 with three parallel or adjacent radiation sources, i.e. transmitter 20a, 20b, 20c.

The transmitter assemblies 10 and 20 are arranged on different sides of the keratin path 51 and the log 50, respectively, i.e. at an angular distance to each other on the opposite point C of the measuring object, but not on diagonally opposite sides (angular distance less than 180 °, e.g. 80 ° to 110 °). On the opposite side of 15, there is a receiver member 30 and 40, respectively, arranged for each transmitter assembly 10, 20. Otherwise, the arrangement is similar to that in Figure 1.

The receiver means comprise about a hundred detectors, such as 30a, 40a, and all transmitter configurations and receiver means are fixed.

Each radiation source 10a, etc., emits an expanding beam 25 having boundary beams such as 10a ', 10a "and 20a', 20a", etc., respectively, which impinges on the entire opposite receiver member 30 and 40, respectively. / 40 are mainly measuring directions m 'and m ", respectively, comprising an angle of the order of 90 °. Both transmitter configurations 10, 20 can be activated simultaneously.

Each measuring pair can be arranged in a separate plane which, at a selected distance in the direction of movement of the measuring object, is separated from the plane of another such pair (where the planes are parallel to each other), or several measuring pairs can be arranged in the same 7 98098 plane (e.g. drawing plane).

In the former case, the measuring pairs can in principle be in an arbitrary (but different) position, e.g. on the side of the position according to Fig. 2, the measuring directions m ', m "being roughly perpendicular to each other, but also in the position according to Fig. 3, where the measuring directions m ', m "has an angle of 180 °.

10

In short, the operation of the device according to the invention can be described as follows.

When the radiation source is activated, the intensity remaining after passing through the radiation measuring device is measured in each separate detector in each measuring element. The value obtained in each detector is a measure of the attenuation of the radiation over the distance from the radiation source. Thus, attenuation values are obtained for a large number (e.g. of the order of 500 or 1000) of the radiation path through the log in the entire receiver element.

Upon activation of the next radiation source in the same transmitter configuration, new values are obtained for the new radiation-25 paths. If the change of radiation source can be performed so quickly that the longitudinal displacement of the log 50 between the activation of the radiation source of the first transmitter assembly and the radiation source of the last transmitter assembly is small (e.g., not greater than 1 cm), a set of 30 measurement values is obtained. thick) to a slice of log, i.e., tomographic cross-section.

The computer unit 52 combines the measurement values from all measurement directions (from all measurement pairs) to apply to the same 35 slices. For each such slice, density variations can then be determined, both in size and location within the log.

As an example of a practical evaluation of the device 5 according to Fig. 2 for measuring logs up to a diameter of 600 mm, the following can be mentioned:

The detector assemblies have a length of about 1000 mm and comprise roughly an equal number of separate detectors 10, i.e. spaced 1 mm apart.

The detector assemblies are arranged at a distance Dm = about 1000 mm from the center of the measuring object.

15 Transmitter assemblies comprise three sources at a distance of about 100 mm from each other, i.e. at a considerably greater distance than the distance between the detectors. The transmitter assemblies are located at a distance Ds = about 2000 mm from the center of the 20 measuring objects, i.e. they are basically twice as far as the detector assemblies.

Within the scope of the invention are also e.g. the following options are possible: 25 - the number of measuring pairs is other than two or one; - the detector assembly is curved; the detector assemblies are arranged close to each other and, in the case of curved detector assemblies, are combined into the same arc, in which part of the arc still receives radiation from several radiation sources of the same transmitter assembly and another part of the arc receives radiation from several radiation sources of another transmitter assembly.

Claims (10)

1. A device for examining non-metallic objects ("measurement items") to determine the occurrence, and in particular the position within the measuring object (50), of any elements present therein having a density that deviates from the normal or average of the measurement feed element. density, including at least one transmitting means (10 ') adjacent to the measuring object (50) for transmitting a radiation capable of penetrating the measuring object, and diametrically opposite each transmitting means, on the opposite side of the measuring object, and receiving means constituting a stationary arrangement. (30 ') of discrete detectors (30'a) which are sensitive to said radiation sensitive to said radiation (30') connected to a computer unit (52), characterized in that each transmitter means consists of a plurality of mutually spaced at each other. (s), which are greater than the distance of the detectors (d), located beam sources (10'a) that are This means that all of the radiation sources in a transmitter means in turn transmit radiation to one and the same detector set in which all the detectors thus in turn receive radiation, the cooperating transmitter and receiver means forming a measuring pair which has a main measuring direction (m). 25 Device according to claim 1 with several measuring pairs (10/30, 20/40), characterized in that each measuring pair is arranged in a separate panel. Device according to claim 1 or 2 with two measuring pairs, characterized in that the main measuring directions (m ', m ") of the measuring pairs enclose an angle in the order of 90 °. Device according to claim 1 or 2 with two measuring pairs, characterized in that the main measuring directions (m1, m ") of the measuring pairs enclose an angle in the order of 180 °. Device according to any of the preceding claims, characterized in that the radiation sources are isotope sources and that an individually maneuverable shutter (11'a) is arranged above each radiation source. Device according to any of the preceding claims, characterized in that the radiation sources are X-ray tubes, and the receiver means is a set of scintillation detectors. Device according to any of the preceding claims, characterized in that the number of radiation sources in a transmitter means is three. Apparatus according to any of the preceding claims, characterized in that the number of detectors in the detector set is in the order of hundreds. Device according to any of the preceding claims, characterized in that the beam sources in a transmitter means have a mutual distance (s) of the order of 100 mm. 10. Device according to any of the preceding claims, characterized in that the transmitter means is arranged at substantially twice the distance (Ds) from the center (C) of the measuring device as the detector set. · «L KM) | I t IH