FI88074B - Procedure and equipment for measuring the length of a log passing a measuring point - Google Patents

Description

88074

Method and apparatus for measuring the length of a log passing a measuring point

The invention relates to a method and apparatus for measuring the length of a log passing a measuring point.

When dealing with trees in different processes, measuring their length is an important part of the process. The measurement of the length of the log can be used, for example, to determine the number of trees 10, to determine the point of cutting of the logs, etc. For this purpose, contact-operated devices with members moving according to the movement of the log, such as measuring rollers, have been developed. However, such organs are susceptible to damage and are inaccurate due to the variability of the tree species to be measured and the varying environmental conditions. In addition, the simplicity and lightness of the structure are aimed at, especially in multifunctional machines used in logging, whereby the measuring elements operating on the principle of contact peri-20 are one of the factors hindering the above-mentioned efforts.

The object of the invention is to eliminate the above-mentioned drawbacks and to provide a non-contact measuring method 25 and an apparatus applying this method, which do not have the drawbacks of contact methods and equipment, but which nevertheless can accurately measure the length of the log to be treated.

30

Em. In order to achieve this, the method according to the invention is mainly characterized in that the transmitter belonging to the measuring device directs ultrasonic waves to the measuring point on the log surface. , and the difference between the transmitted waves 2 88074 and the scattered waves determines the length of the log passing the measuring point. The invention is based on the finding that the surface of the raw wood is so uneven that a scattering of 5 wave movements is generated when ultrasound is applied to it. In this case, the scattered wave motion can be received by the receiver from the desired direction, which can be selected to achieve the best measurement accuracy. In addition, the ultrasound is not attenuated too much, so that the resulting signal is large enough to perform an accurate measurement, in addition to which the ultrasonic sensors are reliable and safe to use. The signal from the scattered ultrasound obtained by the receiver can be easily processed electronically according to the principles of signal processing technology.

The scattered ultrasonic waves are preferably received by a receiver separate from the transmitter, whereby the transmission and reception of the ultrasound can be continuous.

20

According to a preferred embodiment, the displacement of the log, i.e. the length of the log passing the measuring point, is determined by determining the total phase shift of the transmitted waves and the scattered waves. This can be done by means of a waveform signal processing technique developed for the measurement method, whereby a phase shift directly proportional to the magnitude can be obtained without, for example, separately determining the speed of the log and the elapsed time to obtain the length. 30

In processing the signal from the measurement, it is preferred that the signal from the scattered ultrasound be combined with a signal based on the frequency of the transmitted ultrasound, which may be a continuous modulating signal or a pulse train for sampling.

Based on the lower frequency component of the obtained signal, the total shift can be determined using the calculation electronics based on the measurement electronics described below and trigonometric formulas. There may be two signals to be connected to the same signal, in which case they most preferably have a 90 ° phase shift with respect to each other. In this case, the phase difference of the low-frequency components of the two signals obtained can be used to determine the total magnitude and direction of the phase shift between the transmitted waves and the reflected waves.

The measurement is preferably performed in the wood-feeding part of a multifunction machine moving in the field, where the method used is particularly useful.

The apparatus according to the invention, in turn, is characterized in that it comprises a measuring device with an ultrasonic transmitter directed to the measuring point and a receiver positioned relative to the direction of movement of the log so that Doppler displacement occurs in the ultrasonic waves 20 scattering through the measuring point. to register the displacement and to determine the length of the log of the calculation part on the basis of the above information.

25 In addition, the apparatus has some advantageous alternatives which are implemented in such a way that they can take advantage of some of the solutions according to the method alternatives described above. When using the equipment in a grapple processor arranged to feed 30 tree trunks, the transmitter and receiver of the measuring device are preferably located at a point where the distance between the measuring point and the ultrasonic sensors remains as constant as possible.

The invention will now be described in more detail with reference to the accompanying drawings, in which 4 88074 Fig. 1 schematically shows the possible wave motion scattering of the measurement, Fig. 2 schematically shows the Doppler effect 5, Fig. 3 shows some alternatives for positioning the transmitter and receiver Fig. 4 shows another alternative for placing the transmitter and receiver. Figures 5-7 illustrate the processing possibilities of the measurement signal, Fig. 8 schematically shows the processing steps of the measurement signal, and Fig. 9 shows the location of the measuring device in the grapple processor of the single-handed harvester.

Figures 1 and 2 illustrate the generation of a Doppler shift when ultrasonic wave motion is reflected from a moving plane. On the left side of Fig. 1, the surface is flat with respect to the wavelength, whereby most of the wave motion is reflected in the direction b according to the magnitude of the incident angle. On the right side of the surface, the grain size of the object 2 moving in the direction v, such as the log 30, is of the wavelength range, and the wave motion scattering from the surface, i.e. a sufficiently high intensity can be detected in directions other than b. For example, reflection in arbitrary direction a corresponding signal.

5,88074

Figure 2 shows in more detail the conditions for performing the measurement using ultrasound-detectable Doppler shift. The left is shown in general form the formation of a Doppler shift as the particle 5 moves away from the ultrasonic transducers. S1 is the ultrasonic transmitter and S2 is the ultrasonic receiver. The signal from the transmitter to the target is delayed and attenuated due to ultrasonic adsorption and Doppler shift. In addition, x (t) is the location of the particle and v its velocity. 10 The right figure shows the effect of particle motion direction and sensor location on Doppler shift. These can be connected by an angle β = (α + Ϋ / 2), which is the acute angle between the bisector (f) of the angle (f) formed by the wave paths 15 between the transmitter and the reflection point and the reflection point and the receiver (the arrow representing the velocity v). Then xd (t) describes the Doppler shift component of the motion x (t) and xd (t) = x (t) cos (β).

20

right sides of the images 1 and 2, it is evident that the uneven surface of the traveling speed in the direction of the arrow, and forming the reflection points can be continuously detected just em. 25 due to the speed component of the Doppler shift. In order to detect a Doppler shift from a moving surface, scattering caused by surface roughness and the frequency of the correctly selected wave motion is a prerequisite, because according to the main direction of the surface in Figure 1, there is no Doppler shift in the b-wave motion.

Based on Figure 2, the following formula can be derived for the Doppler shift: S, = sin (iot) (1) S2 = A sin (cj (t - 2 x (t) / c)) 35 6 38074 where x (t) = object location at time t 60 = 2nf = angular frequency of the ultrasonic signal 5 c = ultrasonic velocity in air A = attenuation factor

The Doppler shift is affected by the motion component along the wave motion of the particle. Thus, a phase change occurs 10 whenever the direction of motion of the particle deviates from the perpendicular to the wave motion. Taking into account the above effect of transmitter position, reflection point, receiver position and surface motion direction on the above motion component, the signal given by receiver 15 is given the formula: S2 = A sin (co (t - 2cos (β) x (t) / c)) (2) ( β = a + t / 2) 20 When the target is a moving surface uneven with respect to the wavelength of the wave motion instead of a particle, the radial motion component of the surface plane causes a Doppler shift, provided that the surface roughness is of the order of the radiation wavelength or 25. In this case, the surface can be understood as a surface formed by successive individual particles moving in the same direction, as shown on the right-hand side of Fig. 1. The surface roughness of the wood is usually at least a millimeter. Millimeter 30 wavelengths in air are again generated by 340 kHz ultrasound.

Thus, the higher the frequency used, the more certain the occurrence of the Doppler shift. On the other hand, the attenuation of ultra-35 sound in air increases strongly as a function of frequency. Because the Doppler measurement receives a scattered oblique reflection from the wood, the significance of attenuation increases compared to the perpendicular reflected 7 B8074 ultrasound measurement. Especially when aiming for continuous phase shift measurement, it is advisable to use an ultrasound of about 100-200 kHz with the current sensor technology. However, depending on the smoothness of the wood surface, the frequency 5 used may vary between 100 and 500 kHz. The frequency used may be higher as the sensors evolve.

Figure 3 shows some of the placement options 10 of the transmitter S1 and the receiver S2 of the measuring device 1 perpendicular to the direction of movement of the log. The ultrasonic beam of the transmitter sensor S1 is directed at the measuring point on the wood surface 2 to a certain area 3. In Fig. 3 the ultrasonic sensors are aligned on the side of the log with respect to the measured direction v, i.e. their transmitting and receiving beams bisectors ml and m2 are located in plane. In Fig. 4, which shows a second arrangement of sensors from the side, top and perspective, the transmitter 20 S1 and the receiver S2 are placed at the same constant distance h from the log surface 2. In Fig. 4 the placement is optimized so that the transmitter and receiver beam halves ml and m2 the bisector m of the angle formed by the log is in a plane parallel to the direction 2 of movement of the log, perpendicular to the surface 2, and the transmitter and receiver beams are located symmetrically with respect to said direction v when viewed against the surface 2. In Fig. 4, this sharp angle between the bisector m and the direction of movement v is denoted by 30a, as in Fig. 2. Due to the arrangement in Fig. 4, the angle α is then equal to the angle β in Fig. 2, and replaces B in the previous formulas. In the perspective view of Fig. 4, the average plane of the surface is depicted by the x-y coordinate system, where x coincides with the direction of movement v of the surface 35 2.

What the placement of both Figures 3 and 4 has in common is that the bisector m, which determines the angle β of the underlying formulas e 88074, is in the same plane as the direction of movement v of the individual points of the surface 2. In terms of resolution, this is optimal placement.

5 The distance between the log and the sensors should be as constant as possible. In the grapple processor 4 of the single-lever harvester shown in Fig. 9, the best location for the sensors of the measuring device 1 is on the back of the grapple, i.e. the transmitter sensor S1 is then directed towards the grapple opening-10. The sensors are preferably located quite close to the surface of the wood, which reduces e.g. error in measurement caused by air currents and ultrasonic absorption in air. Depending on the type of device, it is always possible to select the optimal location for the measuring device 1, in which the above-mentioned factors have been taken into account.

As shown on the left side of Fig. 3, from the point of view of the measurement resolution, it would be advantageous to place both the transmitting and the receiving sensor side by side 20 as parallel as possible with respect to the measured movement, i.e. the angle β is then small. In this case, however, the intensity of the back scattering sound decreases as each individual reflection angle steepens and the angular deviation Δ β due to the beam width increases. 25 The most effective way to Δ fi: disturbances in a reduced three right-side image in accordance with increasing the beam measurement range of 3 mutually formed by the angle, and placing the receiving sensor S2 is farther away from the measurement area 3 and its vastaanottokeilan and the direction of movement v 30 the angle between the lower this position draft caused by the air currents increase. The compromise is one of the placements in Figure 3, depending on the conditions and sensors used. In the arrangement of Figure 4, the same observation can be made in the plane formed by the bisector bisector-3 en ml and m2, which is located at a constant angle to the x-y plane.

9 88074

According to formula (2), the displacement of the object is obtained from the phase of the received signal, taking into account the coefficients obtained from the reflection angles and the wavelength. The absolute value of the phase of the signal is modulated by a constant phase carrier frequency signal obtained from the transmission signal. The sign of the phase (direction of surface movement) is obtained by combining the modulation in phase shift with the previous signal. Since the measurement distance will vary several wavelengths during the 10 measurements, the direction of the phase shift must also be measured continuously when measuring the total i ithrust of the log in one direction only. The phase shift should deviate from 0 ° and 180 ° and have an optimum magnitude of 90 °. In the following, the expression of 15 steps is presented mathematically.

S! (0) = sin (ω t)

Sj (90) = cos (odd) (3) S2 = A sin (60 (t - 2xd (t) / c)) 20

According to the basic trigonometric formulas, the following holds: sin a sin β = ^ cos (a - β) - cos (a + β)] cos a sin β = Jjfsinfa + β) - s in (a. - β)] 25 Sj (0) xS2 = (A / 2) [cos (oo 2xd (t) / c) - cos (oo2 (t-xd (t) / c))] Sj (90) xS2 = (A / 2) [-sin (co2xd ( t) / c) + sin (w2 (t-xd (t) / c))]

Since xd (t) / c << t at input speeds commonly used in input devices such as multifunction 20, the second component of the two preceding expressions can be removed by ideal low-pass filtering, whereby the modulated signals after filtering are represented by the following formulas:

Zt = (A / 2) [COS (C <J 2 xd (t) / c)] Z2 = (-A / 2) [sin (U) 2 xd (t) / c)] (4) 35 10 88074 Combining these gives the phase and the transition from it: => Z2 / Z, = -tan (c <j2 xd (t) / c) => 2 xda) 60 / c = -arctan (Z2 / Z1); 5 xd (t) = X (ticos (B) (Fig.2) -> x (t) --- 2-arctan (Z2 / Z,) (5) 2 CJ cos (β)

Figure 5 illustrates the modulation described above. The upper figure shows the sinusoidal transmission signal and the received signal S2, and the lower figure shows a solid line illustrating the signal S1 (0) xS2 obtained by modulating the transmission signal with a phase-locked sinusoidal signal and the dashed line 15

The modulated signal can also be modified from a square wave in phase with the transmission signal, whereby modulation takes place by changing the sign of the received signal amplification on the square waves using operational amplifiers or analog multipliers controlled by analog switches. The received signal is then multiplied by square waves as opposed to formula (3), where multiplication is done by sine waves. Unless the signal spectrum contains significant power in the vicinity of the harmonic components of the square wave, after sufficiently steep low-pass filtering, the result is the same. For practical applications of modulating with square waves, the filter must be steeper and even more expensive. As ready-made IC circuits, modulators are also currently more advantageous than analog multipliers. Figure 6 illustrates modulation with square waves according to Figure 5.

Figure 7 shows another alternative in principle corresponding to modulation. Here, the received signal S2 is sampled at a frequency which is 35 I i n 38074 of the transmission signal frequency or divided by an integer. Half of the sampling frequency corresponds to the largest Doppler frequency shift that can be expressed. For example, when β: η is 30 ° and the transmission signal 220 5 kHz has a minimum sampling rate of 12 kHz at a maximum log transmission rate of 5 m / s. In this case, the sampling frequency could be 220 kHz divided by some integer 1..18. The figure below shows a signal obtained by a sample-hold-10 circuit with a pulse train locked to the phase of a transmission signal, which is a pre-low-filtered low-frequency signal. Avoiding low-pass filtering reduces the cost of signal processing electronics.

Sampling can also be performed with an A / D converter by locking the sampling moment to the phase of the transmission signal, whereby the received signal can be further processed by means of digital computation.

In all the alternatives shown in Figs. 5-7, a second low-frequency signal is generated by the modulating signal or the sampling pulse train with respect to the sampling pulse train, and further processing of the obtained signals Z1 and Z2 is performed according to formula (5). The information provided by the parallel signal can be used to determine the direction of movement. In the figures, the frequency of the received signal is higher than that of the transmitted signal, which is due to the opposite direction of movement v compared to Figs. Method 30 works and the formulas are valid regardless of whether the frequency increases or decreases in the Doppler shift.

As can be seen from Equation 5, the coefficient of the arcustangent expression is constant, and the total offset can be determined by continuously monitoring the increase in the absolute value of the arcustangent of the quotient of signals modulated in the above manner. Continuously calculating the arc tangent is possible with analog technology. Continuous phase shift measurement 12 88074 to determine the total offset always requires consideration of ± π: η overruns and summation in the arc tangent calculation.

5 Another option based on the determination of the arc tangent is to trigger with the signals and the Z2 counter and determine the counting direction from them, for example with a D-flip-flop. In this case, the resolution is always the counter LSB, which would be, for example, with the above-mentioned 220 kHz frequency ultrasound, about 1.4 mm when cos (B) = 0.5 (β shown in Fig. 2). Calculating the arc tangent by analogy brings a much better resolution, but the implementation, on the other hand, is more complex and probably more expensive.

15 The third option is to A / D convert the signals at the beginning and modify the measurement result numerically with the above algorithms. The A / D conversion of the signal S2 requires more than twice the frequency of the incoming signal, i.e. its sampling frequency would be about 500 kHz 20 and the sampling frequency required for the A / D conversion of signals Z1 and Z2 would be 12 kHz when the maximum log speed is 5 m / s and the frequency and cos (D) are the same as above.

25 The above-mentioned measurement connection alternatives are shown schematically in Figure 5, which diagram shows two principle connections for Doppler shift measurement. In both, the received signal is modulated and low-pass filtered according to formulas (3) and (4), which also contain the expressions of the signals S. In part I delimited by dashed lines, the phase is expressed analogously by taking the arc tangent and summing the ± ττ: η crossings, the number of wavelengths of the transmission signal multiplied by l / (2cos (B)) multiplied by 35 corresponds to the displacement, i.e. the length of the log past the measuring point. In Part II, a counter is used. From the modulated signals Z1 and Z2, square waves are formed by comparators, from which an offset is obtained with an up / down I 1 13 88074 counter in the wavelengths of the transmission signal by a factor of 1 / (2cos (B)). The direction of the transition is obtained with the D-flip-flop such that the value of Ζ2 ·· η at the rising edge of Z ^ determines the direction of descent.

5

The measurement of the length of a log according to the invention can be applied in all wood feeding devices, especially in multifunctional machines moving in the terrain. The above-mentioned measurement automation can be combined in a manner known per se with the further processing of the measurement data for their storage, calculation and real-time display. The display in the cab of the food processor can continuously indicate in real time the displacement of the tree trunk past the measuring point, so that the data 15 can be used to cut logs of the correct length and the readings can always be reset after each cut. The values obtained in the processing of the measurement signals can be converted into a readable and storable form by means known per se by means of a calculation section 20, which may include analog and digital electronics. As can be seen from Fig. 9, the measuring device 1 may be located in a grapple processor 4 or a similar multifunction machine for feeding, pruning and cutting the tree trunks between the feed members 5 and the cutting-edge 6 in the wood feeding direction after the pruning blades 7.

In practice, the effect of different coefficients and environmental factors can be taken into account by calibrating the calculation-30 part by means of a test measurement, where in the case of a grapple processor the proportion of logs passing the measurement point can be marked with a saw, the distance between marks can be measured and compared with hardware.

35 In addition to real-time use, measurement data can also be recorded, so that they, combined with diameter measurement, can be used to determine the total volume of wood treated.

Claims (11)

1. A method for measuring the length of a stock soin passes the measuring station (3), characterized in that a transmitter (SI) belonging to the measuring device (3) is directed to the measuring station (3) on the surface of the log (2) ultrasonic paths which are on the so directed and for its path length such that the movement of the surface of the log (2) results in a Doppler displacement in the ultrasonic propagating away from the surface 10, said scattered walls are received with a receiver (S2) belonging to the measuring device, and on the base of the the difference between the transmitted walls and the scattered weights is determined the length of the log passed through the measuring station. 15 Method according to claim 1, characterized in that the scattered ultrasonic paths are received with one or more separate receivers (S2) from the transmitter (S1). 20 Method according to claim 1 or 2, characterized in that the length of the log is determined by determining the total size of the fixed displacement between the transmitted walls and the spread walls. . ·. : 25 Method according to claim 3, characterized in. hence, in the signal generated from the scattered ultrasonic paths, a signal based on the frequency of the transmitted ultrasound signal is generated to produce a signal of lower frequency than the aforementioned signals, and the total size of the phase shift is measured from the lower signal of said signal. 5. A method according to claim 4, characterized in that another signal of lower frequency is developed by incorporating in the signal from the scattered paths another signal based on the frequency of the transmitted ultrasonic signals having the same frequency, but a some phase offset, preferably 90 °, with respect to the first, and the total phase offset is determined by comparing the two evoked signals at lower frequency. 5 Method according to any of the preceding claims, characterized in that the measurement is carried out in the tree-feeding part (4) of a movable multifunctional machine, as in a gripping processor. 10 Apparatus for measuring the length of a log passing the measuring station (3), characterized in that it comprises a measuring device (1) with a transmitter (S1) directed for ultrasonic paths (S1) and their receivers (S2), which are positioned relative to the direction of movement of the log (v) such that in the ultrasonic paths transmitted through the measuring station (3) to the receiver (S2) a Doppler displacement occurs, the apparatus further exhibiting an electronic portion for recording the Doppler displacement and a counting part for determining the log length on the basis of the aforementioned data. 8. Apparatus according to claim 7, characterized in that the transmitter (S1) and the receiver (S2) lie separately, the ultrasonic cone developed from the transmitter (S1) and the cone coming into the receiver (S2) forming an angle between them. 9. Apparatus according to claim 7 or 8, characterized in that the counter portion is arranged to determine the total size of the phase shift between the transmitted walls and the scattered walls. '35 10. Apparatus according to claim 9, characterized in that the electronics part comprises means for generating a signal based on the signal to be transmitted and for incorporating it into the signal from the scattered walls 19 88074 to produce a signal of a lower frequency than the aforementioned. the signals, and the counting portion comprises means for calculating the total magnitude of the phase shift on the basis of the lower frequency signal. Apparatus according to any of the preceding claims 7-10, characterized in that the measuring device (1) is located in the tree-feeding part (4) of a movable multifunctional machine.