Proceedings of the Tomsk Order of the October Revolution and Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov

Volume 296
1976

A System for Automatic Reading of Tabular Volumes of Round Timber in the Technological Flow of Wood Bucking and Sorting

V. I. Gorbunov, G. V. Pakhomov

The manual method of accounting for raw material in a modern high-speed technological flow of bucking and sorting restrains the automation of the principal wood-processing operations and does not allow the data obtained to be used for operational control of the enterprise’s production cycle. The introduction of automated control systems for individual technological operations at enterprises of the forestry and woodworking industry necessitates the development of technical means for automatic remote accounting of wood raw material.

Despite the large number of domestic and foreign developments of devices for measuring the geometric dimensions of round timber, an optimal variant has not yet been found. The main problem in creating systems for automatic reading of cubic volume is the lack of reliable devices for measuring the diameter and length of timber materials that would fully satisfy the requirements of the existing technological flow.

Thus, for example, mechanical flap-type automatic volume meters are acceptable only at relatively low conveyor speeds. For photoelectric sensors under the conditions of the forestry and woodworking industry, as a rule, additional sealing devices with transparent walls are required; these, in turn, require devices to protect the walls from dust, water vapor, snow, etc., which reduces reliability of operation or unjustifiably complicates their design. In addition, photoelectric sensors are sensitive to accidental changes in the edge of the log (bark peeling, various deposits, etc.), which lead to additional errors [1].

A contactless system is proposed for automatic reading of cubic volume, in which radioisotope log-size meters implementing the shadow method are used.

The log-size meters operate in the mode of radioisotope relays, since determining the diameter from the attenuation of radiation is difficult because the magnitude of the latter is a complex function of diameter, moisture content, density, and various inhomogeneities of the internal structure of the wood [2].

In the USSR only one method of accounting for round timber has been adopted, namely, by measuring the diameter at the upper cut (end face), the length of the logs, and determining the volume from the tables of GOST 2708-44. When calculat—

when determining volume, mandatory allowances and deviations are used; when the gradation of length is violated, the volume is determined by the nearest smaller standard length, depending on their purpose. It is impossible to obtain exact values of tabular volumes corresponding to GOST 2708-44 by any formula, since the tables were compiled on the basis of processing statistical data. The most accurate values of tabular volumes in an automatic cubage-reading system can be obtained by using a computing device in whose memory the tabular volumes of all possible sizes are recorded for each specific case, but the memory unit of such a device becomes complex even for small assortment tasks.

In the device proposed by the authors, the volume of logs is calculated by the approximate empirical formula

\[ Q = k \frac{\pi d^2 l}{4}, \tag{1} \]

where \(Q\) is the value of the tabular volume;
\(d\) is the diameter of the log at the top end;
\(l\) is the length of the log;
\(k = f(l)\cdot \varphi(d)\) is a coefficient depending on \(l\) and \(d\), introduced into formula (1) for converting the volume of a cylinder into a tabular one.

The function \(f(l)\) can be represented in the form \(f(l)=0.0025l^2-0.05l+1.115\), and

\[ \varphi(d)=\left(1+\frac{d^2}{32}-2d+29.8\right)\cdot 10^{-2} \]

for \(d \le 24\) cm and \(l=5\) and 6 m, and \(\varphi(d)=1\) for \(d \ge 24\) cm for all lengths, and \(\varphi(d)=0.975\) for \(d<24\) cm and \(l=2\) and 3 m.

Figure 1 shows the dependence of the relative error in measuring the volume calculated by formula 1 in comparison with the tabular value, where curve 1 is without taking into account the function \(\varphi(d)\), and curve 2 is with this function taken into account. For mass calculation of log volumes over the entire range of \(l\) and \(d\), the error does not exceed \(\pm 2\%\).

To simplify the device implementing the function \(\varphi(d)\), the range of log diameters for lengths of 5 and 6 m is divided into subranges:

\[ 12 \le d < 14\ \text{cm}, \qquad 14 \le d < 18\ \text{cm}, \qquad 18 \le d < 22\ \text{cm} \]

and for lengths of 2 m—\(16 \le d \le 22\) cm.

The structural diagram of the device for reading the volume of timber consists of a length-measuring unit, a diameter-measuring unit, and computing and digital-printing units.

Figure 2 presents a block diagram of length measurement. Narrowly collimated beams of radiation from beta sources (\(I_1 \ldots I_N\)—basic; INO—counting-start; \(I_1 \ldots I_N\)—precise) are recorded by the corresponding ionizing-radiation detectors (\(D_1 \ldots D_N\), DNO, \(D_1 \ldots D_n\)).

The beta sources and the corresponding ionizing-radiation detectors are installed along the conveyor in accordance with the timber lengths specified in the existing GOST 2292-66 and are connected to the electronic length-measurement circuit. The length-measurement circuit includes the following elements: ADI—amplitude discriminator; T—trigger; UVS—time-coincidence unit; NE—inversion circuit; K—key; F—precision shaper. The outputs of the length-measurement circuit are connected to a bank of timed basic shapers (waiting multivibrators) and to a channel of additional shapers implementing the function \(\varphi(d)\).

The length measurement is performed once relative to the counting-start sensor. The total length of the log is determined by the sum of the pulse durations

Fig. 1. Dependence of the relative measurement error of volumes on the diameter and length of the assortment.

Fig. 2. Block diagram of the diameter meter.

precision and basic forming devices, taking into account the coefficients \(k=f(l)\) for converting the volume of a cylinder into the tabular volume for different lengths of timber, and \(\frac{\pi}{4}\), which are included in formula (1). Information on length enters the computing-device unit when \(d \ge 24\) cm and the channel of additional forming devices when \(d < 24\) cm.

Fig. 3. Diameter-measuring device.

The diameter-measuring device (Fig. 3) consists of a number of beta sources, of which the even-numbered ones 2 are located on one side of log 1, and the odd-numbered ones 3 on the other. The radiation sources are mounted on two posts, the distance between which is 100 cm. The collimated radiation beams create, in a plane perpendicular to the direction of motion of the log, rasters 4, in each of which a radiation receiver 5 is located on the opposite post. In order to eliminate the influence of the source of one raster on the receiver of another and to simplify the design of the collimators, they are staggered along the direction of motion of the log by 10 cm.

Fig. 4. Amplitude analyzer.
Fig. 5. Time diagrams of the amplitude analyzer.

The electronic circuit consists of the count-rate measurement receiver 6, the level amplitude analyzer 7 with matching cascade 8.

Fig. 6. Channel of additional shapers.

Scale marks: 12, 14, 18, 20, 22, 24 cm.

Diagram block labels and inscriptions:

• \(\varphi_k = l_6 d,\quad 12 < d \le 14\)
• AND
• \(\varphi_k = l_5 d,\quad 12 < d < 14\)
• AND

• OR

• \(\varphi_k = f(l_6 d),\quad 14 \le d < 18\)

• AND
• \(\varphi_k = l_5 d,\quad 14 \le d < 18\)
• AND

• OR

• \(\varphi_k = l_6 d,\quad 18 \le d \le 22\)

• AND
• \(\varphi_k = l_5 d,\quad 18 \le d \le 22\)
• AND

• OR

• \(\varphi_k = l_6 d\)

• K
• \(\varphi_k = l_5 d\)

• K

• \(\varphi_k = l_2 d,\quad 16 \le d \le 22\)

• OR
• \(\varphi_k = l_2 d\)
• K

The amplitude analyzer is a diode matrix whose response thresholds are set in accordance with the required diameter-counting increments according to GOST 2292-66 by selecting the resistances of resistors \(R_1 \ldots R_n\) and the value of the divider voltage \(U_n\).

The log, moving along the conveyor, shades the receivers. Information from the unshaded area of the receiver is read by the counting-rate meter and is fed to the amplitude analyzer. As the voltage level changes, depending on the area of the shaded receiver, and the waveform—on the constant of integration (Figs. 4, 5), the diodes \(D_1, D_2\), etc., are opened in succession. The number of transitions, shifted in time, at the output of the amplitude analyzer corresponds to the diameter of the log being measured.

The channel of additional pulse shapers (Fig. 6) comes into operation when there is a reference signal on the bus \(d = 24\) cm. This signal blocks the outputs of the line of time pulse shapers for length measurement and serves as permission for the operation of the first “OR” circuit of the group of diameters, which is triggered when the voltage changes at one of its inputs. This information is fed to the “AND” circuits, the corresponding time pulse shaper that has recorded the length of the log being measured is triggered, and an additional pulse shaper is started, the pulse duration of which is proportional to the value \(k = f(l) \cdot \varphi(d)\), which is then fed to the computing unit. The subsequent “OR” circuits are blocked by a negative voltage from the subsequent buses of the diameter groups.

Information on the length and diameter of the front and rear ends is fed to the program-control device (Fig. 2). The program-control device ensures selection of the upper diameter, automatic operation of the keyed computer (KVM) “Iskra-3,” and the digital printing device F-595 KM. Isotopes Sr-90 with an activity of 8 microcuries are used as sources when operating with STS-5 gas-discharge counters for length measurement, and, for diameter measurement, sources on the order of 100 microcuries with an SBT-10 counter. The modules of the “Ural-10” complex serve as the element base of the automatic log-volume meter.

Thus, the automatic log-volume meter described here satisfies the basic requirements imposed on systems for the automatic reading of volumes of round timber in the forestry and wood-processing industries; that is, it is contactless, applicable at any speeds of longitudinal conveyors, provides the required accuracy, and satisfies the requirements of GOST.

The proposed method is easy to implement, requires no additional design developments, and the automatic log-volume meter consists of electronic units manufactured by industry.

The use of ionizing-radiation sources has advantages over photoelectric sensors (no additional devices are required for protection against external influences, sealing, power supply, etc.).

The use of radioisotopes in devices for recording round timber transported by conveyors at enterprises of the forestry and wood-processing industries opens up broad possibilities for satisfying the requirements imposed on meters of geometric dimensions in the modern high-speed technological flow.

REFERENCES

1. D. D. Matskevich. Methods and Means of Automatic Accounting of Timber in Rafting. Moscow, “Lesnaya promyshlennost,” 1965.

2. A. N. Karmadonov, Yu. I. Litovchenko, V. A. Trudinin, et al. On the choice of a method for monitoring wood. In the collection: Investigation of the Properties of Wood and Wood Materials. Krasnoyarsk, 1969.