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This invention relates to an apparatus for mea¬ suring the diameter of logs in a log-feeding device included in a barking machine of the rotation ring type, said feeding device comprising at least three, 5 and preferably precisely three, rotary feed and/or support rollers movable in a coordinated manner sub¬ stantially radially relative to the centre of the machine by means of a link system. State of the art

10 In general, barking machines of the above type are used in sawmills where they precede the different sawing devices of the sawmill and are disposed prima¬ rily in conjunction with the block-sawing machines where, in an initial step, the log is slabbed on two

15 opposing sides. Before a log is fed into the block- sawing machine, this must be re-set, i.e. the saw means of the machine must be adjusted in dependence upon the diameter of the log. This means that the diameter of the barked log must be determined before

20 slabbing the log.

Hitherto, such measurement of the log diameter has been carried out substantially by optical methods. In this context, the optical measuring devices however suffer from several drawbacks. For instance, they

25 are easily affected by pieces of bark and similar waste products which may accompany the log from the barking machine. Further, logs do not generally have a circular cross-section but a substantially oval one. Therefore, when using traditional optical measur-

30 ing devices, there is a risk that only the extreme log diameter values are had, i.e. maximum or minimum log diameter, which may entail that the block-sawing machine is not re-set for optimal processing of the log.

Brief account of the inventive concept

The present invention aims at overcoming the above-mentioned drawbacks inherent in prior art op¬ tical measuring devices by providing an apparatus for measuring the diameter of logs which is able in a simple and most reliable manner to measure the average diameter of the log. According to the invention, this is achieved by means of an apparatus which is charac¬ terized in that a transducer, preferably in the form of a potentiometer, connected to a computing device is adapted to sense the radial positions and/or move¬ ments of the rollers and to continuously or intermit¬ tently transmit to said computing device the measured values received when a log is fed through the feeding device.

Brief description of the accompanying drawing

In the drawing, Fig. 1 shows the outfeed side of a barking machine comprising a log-feeding device which in accordance with the invention is provided with a transducer, and Fig. 2 shows the upper part of the same barking machine as seen from the side. Detailed description of a preferred embodiment of the invention

In Fig. 1, a barking machine of the rotation ring type is designated 1 and a log-feeding device included therein is designated 2. 3 designates three spiked rollers which form part of the log-feeding device and each of which is mounted on a pivot arm 4. On the pivot shaft of each arm, two relatively short levers 5, 5', 6, 6', 7, 7' are fixedly mounted, the levers facing each other being interconnected by means of link arms 9, 9 ¹ , 9". On one of the pivot shafts, in this case the uppermost, a further, rela¬ tively short lever 8 is fixedly mounted, to which suitably hydropneumatic resilient means 10 is con¬ nected. By this design, the rollers 3 are movable in a coordinated manner towards and away from the

centre of the barking machine by means of the link arms 9 and the levers 5, 6 and 7. The force applied by the resilient means 10 to the link system will load all the rollers 3 equally. A transducer in the form of a potentiometer 11 fixedly mounted on the barking machine 1 is articulated to the lever 8. This transducer senses the position of the lever 8 and, hence, indirectly the position of the rollers 3. Since the position of the rollers is determined by the dia- meter of a log being fed between the rollers, the values received from the transducer provide a basis for calculating the diameter of the part of the log situated between the rollers. In Fig. 2, it is shown how the transducer is arranged at the outfeed side of the barking machine and how the feeding device including rollers, pivot arms 13 and resilient means 17 is arranged at the infeed side. Drive motors 12 are also shown. These parts are however of no major interest for the description of the invention. A small-size computer (not shown) is connected to the transducer. The computer unit is equipped with required modules for computing the diameter of the logs on the basis of the values received from the transducer, for presentation thereof on a display and for communication with a control device for block- sawing machines. In this context, it should be pointed out that the use of precisely three radially, coordi¬ natedly movable rolls or rollers for sensing the log diameter provides a most adequate approximation of the diameter of the log since all three rollers are not likely at the same- time to be on one of the extreme log values. The measured values will not be appreciably affected by the penetration of the spikes into the wood since the force of application of the rollers produced by the resilient means varies in dependence upon the extent to which the rollers are swung out from the centre. Thus, the force of application will

be relatively small for small log dimensions when only a few spikes are engaging the log, and greater for larger log dimensions when several spikes are engaging the log. In this manner, the depth of penetration of the spikes into the log will be maintained prac¬ tically constant. Function of the invention

When the rollers are affected by the log being fed between them, an impulse is supplied to the mea- suring equipment which then initiates the measuring operation. The transducer is read, preferably in a num¬ ber of preset points at the top end and once at the butt end to check that the log is turned right way round. The positions for initiating the measurement may of course be changed. For setting the block-sawing machines, use is made of the minimum diameter value measured. To eliminate any system error, the diameter value corre¬ sponding to the innermost position of the feed rollers can be changed, i.e. the entire diameter scale can be changed by a constant value.

In a preferred embodiment, use is made of a linear potentiometer connected to the lever 8. This means that a circular movement is transformed into a linear movement, which entails that the values received from the transducer do not have a linear relationship.

This is taken into account by dividing the measuring range of the potentiometer into a number of linear sections, and the diameters of the logs are calculated on the basis thereof. Advantages of the invention

The inventive measuring apparatus provides a most accurate measuring value of the average diameter of the log. This value is so exact that it can be used, in con¬ nection with a length measurement, e.g. by means of a photo cell and a pulse meter, for wood value determina¬ tions, i.e. for establishing the compensation a supplier should receive for the timber he has supplied.

Other major advantages of the apparatus according to the invention are that it can easily be mounted on existing barking machines and that it is very in¬ expensive to manufacture since the rollers included therein can be used as sensing means together with a relatively inexpensive potentiometer which can easily be mounted on the barking machine without any major modifications thereof.

Yet another advantage is that the transducer can be connected to a small-size computer unit which contains a queue register and can be connected to a servo-mechanism for automatic re-setting of the block-sawing machines. The number of logs having passed through the barking machine and been measured is input in the queue register together with the respective measured values, whereupon the block-sawing machine is re-set when the respective log passes a transducer, e.g. in the form of a photo cell, arranged in con¬ junction with the block-sawing machine. In this way, a practically automatic handling of the logs is achiev¬ ed. Such automation may be difficult to achieve by traditional optical measuring techniques since the measuring results then obtained must be carefully checked because the optical measuring instruments are easily disturbed by bark fragments etc. Possible modifications of the invention

The invention may of course be modified within the scope of the accompanying claims. Thus, for instance, the transducer need not be a linearly operating po- tentiometer but may instead be a circular potentiometer having substantially the same radius as the lever on which it is mounted. The transducer may also consist of a pulse transducer and need not necessarily be mounted precisely on the lever described above, but may be connected to any suitable, movable part of the mechanism controlling the radial movements of the rollers, including locations on or in the resi-

lient means. Further, the rollers need not necessarily be driving but may for instance have a supporting func¬ tion only. The above-described apparatus for measuring the diameter of logs may particularly advantageous- ly be combined with an apparatus for measuring the length of the logs, which is connected to one and the same computer unit. Such a length measuring appa¬ ratus may consist of a pulse transducer and two photo cells one of which is placed in front of the feeding device 2 and the other behind it.