WO2012087220A1

WO2012087220A1 - Apparatus and method for cut-to-length logging

Info

Publication number: WO2012087220A1
Application number: PCT/SE2011/051415
Authority: WO
Inventors: Gösta FORSÉN
Original assignee: Fotonic I Norden Ab
Priority date: 2010-12-22
Filing date: 2011-11-24
Publication date: 2012-06-28
Also published as: SE1350895A1; SE536770C2; FI126166B; FI20135783A

Abstract

The present invention relates to an apparatus operative to control a cut to- length harvester head during feeding and cutting of a tree trunk to obtain a log of desired length Ld. The apparatus comprises a laser-Doppler sensor adapted and configured for real-time reading of trunk surface velocity (v), a processing unit adapted and configured to receive, and register in a memory unit, real-time surface velocity readings from the laser-Doppler sensor and further to convert registered real-time velocity readings to a corresponding tree trunk transport distance (T). Further the apparatus is adapted and configured to read a longitudinal surface velocity (v) of a trunk being transported longitudinally by means of feeding; register the read surface velocity together with timing information; calculate a relative longitudinal transport distance (T) based on the registered surface velocity and timing information; using the calculated relative transport distance (T) as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length. The invention also relates to a method and a computer program product.

Description

APPARATUS AND METHOD FOR CUT-TO-LENGTH LOGGING

Technical Field

The present invention relates to an apparatus and method for operating and control of cut-to-length logging with minimum spill and in particular to an apparatus and method operative to control a cut-to-length harvester head during feeding and cutting of a tree trunk to obtain a log of desired length.

Background

Mechanized harvesting systems in which trees are delimbed and cut-to-length directly at the stump are often referred to as cut-to-length logging. Cut-to-length logging is typically a two-man, two-machine operation with a harvester felling, delimbing, and bucking trees and a forwarder transporting the logs from the felling to a landing area close to a road accessible by trucks. WO2005043983 and WO2010002339 both disclose measurement wheels for measuring feed length. In particular, WO2010002339 discloses a measurement wheel supported by an arm and provided with an angle sensor. In an extended position, the circumference of the wheel is rolled with retentive force against a longitudinally fed tree trunk. The principle measured magnitude is rotations of the wheel. In order to arrive at a feed length, the number of rotations of the wheel is multiplied by a figure corresponding to the circumference of the wheel. The

measurement wheel method introduces several sources of error. Firstly, angle sensors, as all sensor types, have their specific weaknesses. If subject to harsh conditions, and in particular temperature varying between extremes, an angle sensor may be subject to internal cracking, in which case it will give false readings. Further, the method relies on mechanical contact between the wheel circumference, and that is a weakness. The circumference may slide against a surface covered with mud or ice, or become wedged so that the rotation does not reflect the actual feed of the trunk. Yet further, under dirty and harsh conditions, the wheel may become worn, so that the actual circumference is reduced, or deposits may be building up onto the circumference of the wheel, so that the actual circumference is increased. For the purpose of clarity, it should be mentioned that besides the measurement wheel for measuring tree stem length, WO2005043983 discloses a second measurement device comprising movable photocells. However, it is a measurement device separate from the measurement wheel, and for another purpose, namely for measuring the diameter of the felled tree stem.

Hence, methods that are based on measuring on a proxy object such as a turning wheel are unreliable, give inaccurate results, and a lot of waste, which in turn means reduced returns for the timber producer. It would be desirable to find a method that measures on the actual tree trunk, instead of measuring on a proxy object such as a turning wheel.

Summary

It is the object of the present invention to obviate at least some of the above disadvantages and provide improved methods, apparatuses and computer media products avoiding the above mentioned drawbacks.

A first aspect of the invention is an apparatus operative to control a cut-to- length harvester head during feeding and cutting of a tree trunk to obtain a log of desired length. The apparatus of the first aspect of the invention comprises a laser-

Doppler sensor adapted and configured for real-time reading of trunk surface velocity, which is a function of time. A processing unit is adapted and configured to receive, and register in a memory unit, real-time surface velocity readings from the laser-Doppler sensor and further to convert registered real-time velocity readings to a corresponding tree trunk transport distance. Specifically, said apparatus is adapted and configured to read a longitudinal surface velocity of a trunk being transported longitudinally by means of feeding; register the read surface velocity together with timing information; calculate a relative longitudinal transport distance based on the registered surface velocity and timing information; and using the calculated relative transport distance as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length.

The apparatus of the first aspect may further be adapted and configured to detect a time interval within which no reading is made; to calculate a surface velocity approximation based on surface velocity read before and after the time interval; and to register the calculated surface velocity approximation to complete registering of surface velocity, thereby enabling calculating of a complete transport distance.

The processing unit may further be adapted and configured to comprise Kalman filter functionality.

The laser-Doppler sensor may be arranged in a ventilation channel such that air may be fed around the perimeter of the sensor's aperture, towards the read surface, thereby enabling driving objects away from the sensor's field-of-view. The apparatus of the first aspect may further comprise a fan, located adjacent to the back of the sensor and arranged to feed the air. The apparatus may further comprise an air conduit arranged such that it may supply air without objects to the ventilation channel. A second aspect of the invention is a method for controlling a cut-to length harvester head while feeding and cutting a tree trunk to a desired length. The method comprises the steps of reading with a laser-Doppler surface velocity sensor a longitudinal surface velocity of a trunk being transported longitudinally by means of feeding; registering the read surface velocity together with timing information;

calculating a relative longitudinal transport distance based on the registered surface velocity and timing information; using the calculated relative transport distance as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length.

The method of the second aspect of the invention may comprise the further steps of detecting a time interval within which no reading is made; approximating a surface velocity based on surface velocity read before and after the time interval;

registering the surface velocity approximation to complete registering of surface velocity, thereby enabling calculating of a complete transport distance.

The calculating step may comprise Kalman filtering as a means to obtain approximations. The method may comprise the further steps of feeding air around the perimeter of the sensor's aperture, towards the read surface, thereby driving away objects from the sensor's field-of-view.

A third aspect of the invention is a computer program comprising program instructions for causing a computer to perform the process of the second aspect of the invention when said product is run on a computer. The computer program of the third aspect of the invention may be embodied on a record medium, stored in a computer memory, embodied on a read-only memory, or carried on an electrical carrier signal.

A fourth aspect of the invention is a computer program product comprising a computer readable medium, having thereon: computer program code means, when said program is loaded, to make the computer execute the process of the second aspect of the invention.

Brief Description of the Drawings

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings, in which

Figure 1 is a view of a harvester system.

Figure 2 is schematic view of a harvester head controllable by an apparatus and method according to the present invention.

Figure 3 is a schematic view of a trunk being fed through the harvester head. Figure 4 is an overview of an apparatus according to the present invention. Figure 5 is a flow-chart illustrating a method according to the present invention. Detailed Description

A solution to the above problems is presented below. Certain reference concepts will be described in reference to Figure 1 , which shows a cut-to-length harvester system 300. Operation and monitoring of operation of the harvester system 300 is enabled by apparatuses and methods according to embodiments of the present invention.

The harvester system 300 comprises a harvester head adapted and configured for gripping, feeding and cutting a tree trunk 10. This means that the system 300 comprises all necessary means and features, such as means for gripping a tree on root, or a felled tree, means for feeding a tree trunk through the harvester head and means for cutting a tree trunk in two. Embodiments of the invention may also be adapted and configured for integrated felling of a tree on root, and delimbing and bucking of a felled tree. During cutting, the tree trunk should be immobile relative the cutting member of the harvester head, at least in the longitudinal direction. Usually grapples or other members of the harvester head keep the tree trunk in a position that is entirely fix. The trunk's longitudinal position relative a cutting plane 30 of the cutting member at the time of cutting may be considered to be a neutral position. A cut may be an initial felling cut, or a subsequent logging cut in a plane 40 at a distance L from the latest cutting plane, as illustrated in figure 2. Figure 2 illustrates the trunk 10 in a neutral position relative the harvester head comprised in the harvester system 300. In each moment in time, relative transport T(t) of the trunk from the neutral position to the momentary transport position indicates the momentary length L(t) between the latest cut and the cutting member plane 30, i.e. where the trunk will be cut to a log of length L_d if the cutting member is activated.

Though T(t) may be measured at a longitudinal distance D from a first cutting plane 30, T(t) is identical to a length L(t), that is T(t)≡L(t), between a first and a second cutting plane 30 and 40 respectively, perpendicular to the longitudinal feed axis. This is illustrated in Figure 3. It is worth noting that a multiple of wheel circumferences is never identical to L(t), though it may be equal within tolerances during favorable circumstances. A cut margin M_c corresponds to the height of the trunk slab being processed to saw dust by the cutting member. If the general feeding and cutting is operated with large tolerances, the cut height is negligible compared to the large overall tolerances.

However, while operating under tolerances as small as those enabled by embodiments of the present invention, cut margin M_c may be of the same magnitude as the tolerances. Therefore, when using T(t) as control input to the feeding and cutting operation, a log of desired length L_d may be obtained if a cutting operation is initiated when T(t)= L_d+M_c.

An apparatus 100 according to embodiments of the present invention will now be described in relation to Figure 4. The apparatus 100 is operative to control a cut-to- length harvester during feeding and cutting of a tree trunk 10 to obtain a log of desired length La. The apparatus 100 comprises a sensor arrangement. The sensor arrangement comprises a sensor 110 adapted for non-contact primary measuring of surface velocity. The sensor 110 may be a laser-Doppler velocity sensor 110. The sensor 110 is adapted to read a surface 20 velocity v(t) of a log 10 being fed past the sensor 110 in its field-of- view. The sensor 110 is so arranged in relation to the harvester that fix or moving parts of the harvester never block line-of-sight between the sensor aperture 115 and the part of the surface 20 to be read. The aperture's 115 line-of-sight is slightly tilted relative a plane perpendicular to the feed axis. The slight tilt enables laser-Doppler reading. The tilt is in the feed direction. This is an advantage because objects moving in the general direction of the feed are thereby in effect moving away from the aperture 115, which in turn means that the risk for clogging of the aperture 115 is reduced.

The sensor 110 is so located in a ventilating channel 120, that air may flow along the side of the sensor 110. Air may flow towards the aperture side of the sensor 110, in the general direction of the sensor's 110 field-of-view. Air may be supplied to the ventilation channel 120 through an air conduit 150 having an outlet 155 in the ventilation channel 120. The air conduit 150 may feed clean air from a location 160 that is sheltered from direct debris or spray from the operating harvester. The shelter may be provided by the harvester head itself, or by a separate shield 165 made for that particular purpose, or a combination of both. The air conduit 150 feeds the clean air into the ventilation channel 120. A fan 140 may be adapted to drive the air through the air conduit 150, through the ventilation channel 120 and past the sensor aperture 115. The fan 140 may be located within the ventilation channel 120. The fan 140 may be located substantially between the air conduit outlet 155 and the sensor 110. The air may also flow on several sides, or flow along the entire perimeter of the sensor 110. Particularly the air may flow at the perimeter of the sensor's aperture 115, so that dirt, precipitation or debris that would otherwise block or dim the field-of-view of the sensor, is driven away. The ventilating channel's outer enclosing surface 130 may be the inner surface of a casing, or the inner surface of cavity within the harvester itself.

The apparatus 100 further comprises a processing unit 112 adapted and configured to receive, and register in a memory unit 114, real-time surface velocity readings from the laser-Doppler sensor 110 and further to convert registered real-time velocity readings to a corresponding tree trunk transport distance T(t), thereby enabling conversion from velocity readings to relative transport T of the trunk, from a neutral position to a current position. The memory unit 114 may also be comprised in the apparatus 100. The apparatus 100 may be distributed within the harvester system 300 such that certain components comprised in the apparatus 100 are located inside or on the harvester head itself, whereas other components, such as e.g. the processing unit 112 and/or the memory unit 114 may be located elsewhere within the harvester system 300.

Because a laser-Doppler sensor 110 is very accurate, the measured relative transport T(t) enables very accurate cut-to-length La. This in turn enables operation under very strict tolerances, typically less than 10 mm tolerance limit.

Felling and bucking is made under harsh conditions that includes precipitation, splinter and debris, that may obscure line-of-sight of an optical sensor of any type, in which case the optic sensor reading may cease for a short periods of time. Transport that takes place when there is no reading will not be registered. This introduces a problem in systems controlled by reading of length. Under such circumstances the system will operate on a length indication that is shorter than the actual transportation. When measuring length it is difficult to distinguish a false reading from a true reading.

However, a laser-Doppler sensor does not give false readings. If the sensor 110 is able to read velocity v(t), the velocity reading v(t) is accurate. If the sensor 110 is not able to read velocity, it will not give a velocity reading. In other words, the processing unit 112 may easily distinguish interruptions.

The problem of how to compensate for a reading interruption is solved through an averaging or approximation functionality implemented in the processor unit 112. As mentioned above all velocity readings are registered together with timing information. Therefore, if an interruption occurs in an interval I between ti and t₂, the

processing unit 112 will know the momentary velocity vi immediately before ti and the momentary velocity v₂ immediately after t₂. The processing unit 112 may use the actual reading values v_{l s} v₂ and the timing information to calculate an approximation of v(t) over the interval I, ti to t₂. The processing unit 112 may use vi and v₂ to calculate a corresponding transport Ti_₂ occurring between tl and t2. This enables a very reliable approximation for two separate, but interacting, reasons: interruptions will likely have a very short duration; and due to the linear momentum of the trunk, acceleration will remain fairly constant. In other words: major change in velocity is unlikely during a short interval.

According to one embodiment, the processing unit 112 uses a Kalman filter to produce estimates or approximations that can be registered instead of actual readings. A Kalman filter may produce approximations of the true values of readings and their associated calculated values by predicting a value.

A method 200 according to an embodiment of the present invention will now be described in relation to figure 5.

The method 200 is a method for controlling a cut-to-length harvester head while feeding and cutting a tree trunk to a desired length Ld. In a reading step 210 the longitudinal surface velocity (v) of a trunk 10 is being read. The trunk 10 is transported longitudinally by means of feeding comprised in the harvester head. The reading may be performed by a laser-Doppler surface velocity sensor 110.

In a registering step 220 the read surface velocity v(t) is registered in the memory unit 114 together with timing information. In a calculating step 260 a relative longitudinal transport distance T(t) based on the registered surface velocity and timing information is calculated.

In an operation control step 270, the calculated relative transport distance (T) is used as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length L_d.

The method 200 may further comprise a detecting step 230, in which the processing unit 112 detects a time interval I within which no reading of v(t) is made. The detecting step 230 is followed by an approximation step 240, where a surface velocity approximation is calculated based on surface velocities read before and after the time interval I; and by a registering step 250 when the calculated surface velocity approximation is registered in the memory unit 114 to complete registering of surface velocity (v). These steps enable calculating of a complete transport distance (T) even though the actual readings are not complete.

According to certain embodiments of the method 200 the approximation step 240 comprises Kalman filtering. The method 200 comprises the further steps of feeding air around the perimeter of the sensor's aperture 115, towards the read surface, thereby driving away objects from the sensor's field-of-view.

The above presented apparatus, method and system provide several advantages compared to previously known solutions.

The laser-Doppler sensor 110 apparatus 100 gives reliable readings.

Further the laser-Doppler sensor apparatus 100 provides a very high accuracy, partly because it operates with high optical resolution.

The system is robust. The integrated fan drives away objects that might otherwise interfere with the optical reading. Because the sensor 110 works according to a one dimensional laser-Doppler principle, revolving of the trunk will not affect measurements

In the event that the optical reading would be obstructed despite of the fan, the system can easily detect a reading pause, and can calculate an estimate with very high accuracy.

Claims

1. An apparatus (100) operative to control a cut-to-length harvester head during feeding and cutting of a tree trunk to obtain a log of desired length (L_d), the apparatus (100) comprising a laser-Doppler sensor (1 10), a processing unit (1 12) and a memory unit (1 14), said apparatus (100) being adapted and configured to perform the steps of

reading (210) with the laser-Doppler surface velocity sensor (1 10) a longitudinal surface velocity (v) of a trunk being transported longitudinally by means of feeding;

registering (220) the read surface velocity together with timing

information;

calculating (260) a relative longitudinal transport distance (T) based on the registered surface velocity and timing information;

using (270) the calculated relative transport distance (T) as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length (L_d).

2. The apparatus (100) according to claim 1 , adapted and configured to perform the further steps of

detecting (230) a time interval (I) within which no reading is made;

approximating (240) a surface velocity based on surface velocity read before and after the time interval (I);

registering (250) the calculated surface velocity approximation to complete registering of surface velocity (v), thereby enabling calculating of a complete transport distance (T).

3. The apparatus (100) according to claim 1 or 2 , further adapted and configured to perform the approximating step (240) comprising Kalman filtering.

4. The apparatus (100) according to claim 1 , wherein the sensor (1 10) is arranged in a ventilation channel such that air may be fed around the perimeter of the sensor's (1 10) aperture (1 15), towards the read surface, thereby enabling driving objects away from the sensor's (1 10) field-of- view.

5. The apparatus (100) according to claim 4 , further comprising a fan located adjacent to the back of the sensor (1 10) and arranged to feed the air.

6. The apparatus (100) according to claim 4 or 5, further comprising an air conduit arranged such that it may supply air without objects to the ventilation channel.

7. A method for controlling a cut-to length harvester head while feeding and cutting a tree trunk to a desired length (Ld) comprising the steps of reading (210) with a laser-Doppler surface velocity sensor (1 10) a longitudinal surface velocity (v) of a trunk being transported longitudinally by means of feeding;

registering (220) the read surface velocity together with timing

information;

using (270) the calculated relative transport distance (T) as input to control the feeding and cutting operation of the harvester head, thereby enabling cutting a log of the desired length (Ld).

8. The method according to claim 7 comprising the further steps of detecting (230) a time interval (I) within which no reading is made;

9. The method according to claim 7 or 8 , the approximating step (240) comprising Kalman filtering.

10. The method according to any of claims 7 to 9, comprising the further steps of feeding air around the perimeter of the sensor's (1 10) aperture (1 15), towards the read surface, thereby driving away objects from the sensor's (1 10) field-of-view.

1 1. A computer program comprising program instructions for causing a computer to perform the process of any of claims 7-10, when said program is run on a computer.

12. A computer program according to claim 11 , embodied on a record medium, stored in a computer memory, embodied on a read-only memory, or carried on an electrical carrier signal.

13. A computer program product comprising a computer readable medium, having thereon: computer program code means, when said program is loaded, to make the computer execute the process of any of the claims 7-10.