Patent Description:
Harvesting heads are used in forestry to cut down trees, limb them, cut the trunk into smaller pieces and while doing this also determine the size of the trees. The sizes that are determined are the length and thickness of the trees' trunks.

A harvesting head usually consists of a rigid frame to which there is attached a pair of front limbing knives, a pair of feeding rollers, a chain saw and sometimes one or two back limbing knives situated between the pair of feeding rollers and the chain saw.

A harvesting head functions as such that it grips a tree by its trunk close to the ground. It then cuts through the trunk and fells the tree. The tree is then fed through the harvesting head, which limbs the tree as it passes therethrough. After feeding through certain lengths of the tree the fed-through parts are cut off, after which the tree is continued to be fed through. When the tree's trunk becomes too thin, the tree is let go off.

Examples of harvesting heads are disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

The limbing knives, the feeding rollers as well as the chain saw are all pivotally movable. The chain saw such that it can move against the tree trunk and saw it through. The feeding rollers such that they can grip the tree trunk and feed it through the harvesting head by rolling. The limbing knives such that they can enclose the trunk and press it against a gliding surface of the harvesting head. A gliding surface is a surface on the harvesting head's frame against which a tree trunk glides when it is fed through the harvesting head.

The length of a tree trunk is measured continuously as a trunk is fed through the harvesting head. The thickness of a tree trunk is determined at several points with a certain length interval. The thickness and length of a tree trunk is used to calculate the volume of the harvested tree.

The thickness of a fed through tree trunk is typically determined by measuring the position of a limbing knife or a feeding roller and relating its position to the frame of the harvesting head, typically the gliding surface. Since the tree trunk is pressed against the frame by either a limbing knife or a feeding roller, the position of the limbing knife or feeding roller will be related to the thickness of the fed through trunk.

Although this method may have an acceptable accuracy for now, it is far from perfect and the determined thickness is too often wrong.

It is an object of the present disclosure to present a method for determining a thickness of a tree trunk in a harvesting head for forestry with increased accuracy. It is also an object of the present disclosure to present a harvesting head for forestry which can determine a thickness of a tree trunk with increased accuracy.

According to an aspect of the invention there is provided a method for determining a thickness of a tree trunk in a harvesting head for forestry, said harvesting head comprising.

A tree trunk surface follower is a device which is arranged to follow the surface of a tree trunk held in a harvesting head, following the movement of the tree trunk surface while the tree trunk is fed through the harvesting head. The tree trunk surface follower may abut the tree trunk surface but does not need to. Ideally, the tree trunk surface follower is placed as close to the tree trunk pressing device as possible, in the feeding direction of the tree trunk, such that the deviation of the tree trunk is determined as close to the measured thickness as possible.

By determining the deviation by measuring the position of a tree trunk surface follower and relating its position to both the reference surface and the measured thickness, the dependence of the position of the tree trunk surface follower on the thickness of a tree trunk can be adjusted for.

Themethod comprises determining a thickness of a tree trunk in a harvesting head for forestry, said harvesting head comprising.

The harvesting head further comprises a proximity sensor, and measuring the position of the tree trunk surface follower is done with the proximity sensor.

According to one embodiment the proximity sensor is a magneto-inductive sensor.

According to one embodiment of the disclosure the tree trunk surface follower is pressed against at least a portion of the half of the circumference of the tree trunk which is closest to the reference surface. In this manner the tree trunk surface follower follows the position of the tree trunk's surface, following the part of the tree trunk which is closest to the reference surface. This assures that the position of the tree trunk surface follower will be related to the deviation of the tree trunk from the reference surface.

According to another aspect of the present disclosure there is provided a method for determining a volume of a tree trunk in a harvesting head by determining a length and several thicknesses of the tree trunk. The determined thicknesses being spaced at a certain length interval. The volume being calculated based on the determined length and thicknesses. The thicknesses being determined according to the previously disclosed method. In this manner a more accurate volume of a tree trunk can be determined. The volume of the tree trunk will be adjusted for any inaccuracies coming from deviations from the reference surface of the tree trunk during volume determining.

According to another aspect of the invention there is provided a harvesting head for forestry, comprising a thickness measuring arrangement for measuring a measured thickness of a tree trunk, said thickness measuring arrangement comprising a tree trunk pressing device, for pressing said tree trunk in a direction towards a reference surface of the harvesting head , and a first measuring sensor arranged to measure the position of said tree trunk pressing device relative to said reference surface,.

According to one embodiment the second measuring sensor is a magneto-inductive measuring sensor.

The limbing member is arranged on a front side of a front plate of the harvesting head, and the second measuring sensor is arranged on a back side of the front plate, the back side being opposite to the front side.

The second measuring sensor comprises a first portion and a second portion, and the first portion is arranged on the front plate and the second portion is arranged on the limbing member.

According to one embodiment the front plate comprises a slit extending through the front plate from the front side to the back side,.

In another embodiment of the present disclosure the tree trunk surface follower is arranged to follow at least a portion of the half of the circumference of the tree trunk which is closest to the reference surface. This embodiment has the advantage of assuring that the tree trunk surface follower follows the position of the tree trunk surface, following the part of the tree trunk which is closest to the reference surface, which in its turn assures that the position of the tree trunk surface follower is related to the deviation of the tree trunk from the reference surface.

The tree trunk surface follower may be pressed towards the tree trunk by a compression spring, a torsion spring or a hydraulic piston.

The tree trunk pressing device may comprise at least one limbing knife.

The tree trunk surface follower may be pivotally coupled to the harvesting head.

The tree trunk surface follower may be linearly guided.

The second measuring sensor may be a contact free linear sensor.

These and other aspects of the invention will be apparent from and elucidated with reference to the claims and the embodiments described hereinafter.

In <FIG> a harvesting head <NUM> for forestry is shown. The harvesting head <NUM> comprises a tree trunk pressing device, in this case a pair of front limbing knives <NUM>, <NUM>, a tree trunk surface follower, in this case a limbing member <NUM>, and a reference surface, in this case a gliding surface <NUM>. The harvesting head <NUM> further comprises a pair of feeding rollers <NUM>, <NUM>, a pair of back limbing knives <NUM>, <NUM>, a chain saw <NUM> and a length measuring wheel <NUM>.

In <FIG> the same harvesting head <NUM> is shown while holding a tree trunk <NUM> and feeding it through itself. The feeding rollers <NUM>, <NUM> are used to grip a tree trunk <NUM> and feed it through the harvesting head <NUM>. The rollers <NUM>, <NUM> are pivotally movable such that they can move towards and away from each other. By moving towards each other they can grip a tree trunk <NUM> between them. By spinning the rollers <NUM> and <NUM> in directions B and C respectively, a gripped tree trunk <NUM> will be moved through the harvesting head <NUM> in a feeding direction A. The limbing knives <NUM>, <NUM> are pivotally movable in a plane perpendicular to the feeding direction A of the tree trunk <NUM> and are used to enclose a tree trunk <NUM> and press it in a direction towards the gliding surface <NUM>. The front limbing knives <NUM>, <NUM> are used to limb a tree trunk <NUM> as well as to determine a thickness of it. The back limbing knives <NUM>, <NUM> are also pivotally movable in a plane perpendicular to the feeding direction A of the tree trunk <NUM> and used to enclose a tree trunk <NUM> and press it in a direction towards the gliding surface <NUM>. The limbing knives <NUM>, <NUM>, <NUM>, <NUM> have the form of curved knives with the sharp end on the front side. An enclosed tree trunk <NUM> will have its limbs cut off by the limbing knives <NUM>, <NUM>, <NUM>, <NUM> when fed through the harvesting head <NUM> in feeding direction A. The chain saw <NUM> is used to cut off limbed pieces of a tree trunk <NUM>. The chain saw <NUM> is held inside a cover <NUM> and is pivotally movable in a plane perpendicular to the feeding direction A of the tree trunk <NUM>. The tree trunk <NUM> is cut by moving the chain saw <NUM> through it.

The limbing member <NUM> is arranged on a front plate <NUM> of the harvesting head. The front plate <NUM> is a plate arranged on the front side of the harvesting head <NUM>. The front side of the harvesting head <NUM> being the side of the harvesting head <NUM> facing towards the feeding direction A. The front plate <NUM> has a front side and a back side. The back side of the front plate <NUM> is the side facing along the feeding direction A. The front side is arranged to face a portion of a tree trunk <NUM> with limbs. The back side is arranged to face a delimbed portion of a tree trunk <NUM>.

The limbing member <NUM> is curved. By this is meant that a portion of the limbing member <NUM> arranged to be closest to a tree trunk <NUM> fed through the harvesting head has a curved shape. This could be a sharp edge, which is comprised by the limbing member, configured to delimb a portion of the circumference of the tree trunk <NUM>. A curved shape could be a continuous curve. A curved shape could be a combination of two or more straight lines or surfaces arranged at an angle relative each other. A curved shape could be a combination of a continuous curve and one or more straight lines or surfaces arranged at an angle relative each other. The limbing member is curved such that it is concave towards the tree trunk.

<FIG> shows how the thickness of a tree trunk <NUM> affects the position of the front limbing knives <NUM>, <NUM>, which press the tree trunk towards the gliding surface <NUM>. A tree trunk <NUM> with a larger thickness T<NUM> will mean that the limbing knives <NUM>, <NUM> are positioned differently than if the tree trunk <NUM> had a smaller thickness T<NUM>. The position of the limbing knives <NUM>, <NUM> relative to the gliding surface <NUM> is thus related to the thickness of a tree trunk <NUM>. A measured thickness of an enclosed tree trunk <NUM> can therefore be determined by measuring the position of the limbing knives <NUM>, <NUM> and relating the position of the limbing knives <NUM>, <NUM> to the gliding surface <NUM>. The thickness determined being the thickness T<NUM>, T<NUM> of the tree trunk <NUM> in a direction perpendicular to the gliding surface <NUM>. In the disclosed embodiment the thickness T<NUM>, T<NUM> is determined by a thickness determining arrangement <NUM>, which comprises the pair of front limbing knives <NUM>, <NUM> and rotary encoders <NUM>. The rotary encoders <NUM> are arranged to measure the angular position of the front limbing knives <NUM>, <NUM>. The angular position of the limbing knives <NUM>, <NUM> is related to the gliding surface <NUM>, and thereby a thickness of a tree trunk <NUM>, through a conversion table which relates different angular positions of the front limbing knives <NUM>, <NUM> to different thicknesses. By measuring the angular position of the front limbing knives <NUM>, <NUM> a measured thickness T<NUM>, T<NUM> of a tree trunk <NUM> is thus obtained.

When determining the thickness of a tree trunk <NUM> using the position of the limbing knives <NUM>, <NUM>, they are assumed to press the tree trunk <NUM> against the gliding surface <NUM> such that the tree trunk <NUM> abuts it. By assuming this, the position of the limbing knives <NUM>, <NUM>, in relation to the gliding surface <NUM>, will be directly related to the thickness of a tree trunk <NUM>. However, if the tree trunk <NUM> for some reason does not abut the gliding surface <NUM> the measured thickness T<NUM>, T<NUM> will be wrong. A common cause of measurement error is a deviation of the tree trunk <NUM> from the gliding surface <NUM>. Such a deviation may occur if the tree trunk <NUM> is curved or if its surface is uneven, for example from a poorly cut off limb.

<FIG> shows a cross sectional view of the harvesting head <NUM> holding a tree trunk <NUM> from <FIG>. In this figure it can clearly be seen that the tree trunk <NUM> has an uneven surface. This unevenness has produced a deviation D of the tree trunk <NUM> from the gliding surface <NUM>. This deviation D is what differs a measured thickness T from a corrected thickness Tc. The corrected thickness Tc being the measured thickness T corrected for the deviation D. The deviation is determined by a deviation measuring arrangement <NUM>, which comprises the limbing member <NUM>, a linear contact sensor <NUM>, a rotational joint <NUM> and a torsion spring situated in the rotational joint <NUM>. The limbing member <NUM> is pivotally coupled to the harvesting head <NUM> by rotational joint <NUM>. The torsion spring presses the limbing member <NUM> towards the tree trunk <NUM> in a direction E by rotating the limbing member <NUM> in direction F. The linear contact sensor <NUM> is mechanically coupled to the limbing member <NUM> by connection <NUM>. The linear contact sensor <NUM> measures the position of the limbing member <NUM>. By measuring the position of the limbing member <NUM> it is possible to measure the deviation D. Since the limbing member <NUM> follows the surface of the tree trunk <NUM> its position can be related to the position of the surface which it follows. If the surface which the tree trunk surface follower follows is on the half of the circumference of the tree trunk <NUM> closest to the gliding surface <NUM>, i.e. the same side which abuts or deviates from the gliding surface <NUM>, the position of the limbing member <NUM> can be directly related to the deviation D of the tree trunk <NUM> from the gliding surface <NUM>. The position of the limbing member <NUM> is related to the gliding surface <NUM>, and thereby a deviation D of a tree trunk <NUM> from the gliding surface <NUM>, through a conversion table which relates different positions of the limbing member <NUM> to different deviations D.

The deviation D is measured at a distance, along the feeding direction A of the tree trunk <NUM>, from where the measured thickness T is measured. The smaller this distance is the better the measured deviation D will correspond to the deviation of the tree trunk <NUM> at the point where the measured thickness T is measured. The distance between where the measured deviation D and the measured thickness T is measured is preferably less than <NUM>.

In <FIG> it is also shown that the length measuring wheel <NUM> is pivotally coupled to the harvesting head <NUM> such that it moves in direction G, when pressed towards the surface of the tree trunk <NUM>. The length measuring wheel <NUM> is pressed towards the surface of the tree trunk <NUM> by means of a hydraulic cylinder <NUM>.

<FIG> show an alternative limbing member <NUM>' to the one shown in <FIG>. The limbing member <NUM>' is linearly guided and pressed towards the tree trunk <NUM> in direction H by compression springs <NUM>. The alternative limbing member's <NUM>' position relative to the gliding surface <NUM> may be measured by a linear contact sensor mechanically coupled to the limbing member <NUM>' or by a contact free linear sensor.

<FIG> shows how the position of a limbing member <NUM> is affected by the thickness of a tree trunk <NUM> abutting it. Compared to a thinner tree trunk <NUM>, a thicker tree trunk <NUM> will shift the position of a limbing member <NUM> away from the tree trunk <NUM>. This is because a thicker tree trunk <NUM> will not abut the limbing member <NUM> at the same points of the limbing member <NUM> as a thinner tree trunk <NUM> will, shifting the limbing member's <NUM> position by a distance I. When measuring the position of the limbing member <NUM>, and thus the deviation D of the tree trunk <NUM> from the gliding surface <NUM>, the position of the limbing member <NUM> may be assumed to only depend on the position of the tree trunk <NUM>. Since this is not true, the position of the limbing member <NUM> also depending on the thickness of the tree trunk <NUM>, an error may be present when determining a deviation D. By also taking into account the relationship between the thickness of the tree trunk <NUM> and the position of the limbing member <NUM>, a more correct deviation D can be obtained. When determining the deviation D of the tree trunk <NUM>, the position of the limbing member <NUM> can then be related to the gliding surface <NUM>, and thereby a deviation D of a tree trunk <NUM> from the gliding surface <NUM>, through a conversion table which relates different positions of the limbing member <NUM> and different measured thicknesses T of the tree trunk <NUM> to different deviations D. Thus determining the deviation D may further comprise relating the position of the limbing member <NUM> to the measured thickness of the tree trunk <NUM>. According to the first aspect of the invention, determining the deviation D of the tree trunk <NUM> from said reference surface <NUM> may be done as a function of said position of the limbing member <NUM>, a curvature of the limbing member <NUM> and the measured thickness (T).

<FIG> shows the back side of a front plate <NUM> of a harvesting head <NUM>. A limbing member <NUM> is arranged on the front side of the front plate <NUM>. A sensor <NUM> is arranged on the back side of front plate <NUM>. The back side being opposite of the front side. The sensor <NUM> is a proximity sensor, a magneto inductive sensor. The sensor <NUM> is arranged to measure the position of the limbing member <NUM>.

The sensor <NUM> comprises a first portion 22a and a second portion 22b. The first portion 22a is arranged on the front plate <NUM>, on the back side of the front plate. The second portion 22b is arranged on the limbing member <NUM>.

The front plate <NUM> comprises a slit <NUM>. The slit <NUM> extends through the front plate <NUM> form the front side to the back side. The second portion of the sensor 22b is arranged in the slit <NUM>.

<FIG> shows the sensor <NUM> of <FIG>. The first portion of the sensor 22a comprises a sensing element <NUM>. The second portion of the sensor 22b comprises a target <NUM>. The target <NUM> is in the form of a magnet. The sensing element <NUM> is configured to sense the presence of the target <NUM>. The sensor <NUM> is configured to output an analog signal linearly proportional to the distance between the sensing element <NUM> and the target <NUM>. The first portion 22a has a casing surrounding the sensing element <NUM>. The second portion 22b has a casing surrounding the target <NUM>.

With reference to <FIG>, <FIG> and <FIG> a method according to the present disclosure will now be described.

A corrected thickness Tc of the tree trunk <NUM> is determined by determining a measured thickness T and a deviation D of the tree trunk <NUM> and calculating a corrected thickness Tc based on the deviation D and the measured thickness T.

The measured thickness T is determined by measuring the angular position of the front limbing knives <NUM>, <NUM>, with the rotary encoders <NUM>, and relating the position of the front limbing knives <NUM>, <NUM> to the gliding surface <NUM>. The angular position of the front limbing knives <NUM>, <NUM> being related to the gliding surface <NUM>, and thereby a measured thickness T, through a conversion table which relates different angular positions of the front limbing knives <NUM>, <NUM> to different thicknesses T of a tree trunk <NUM> held in the harvesting head <NUM>.

The deviation D is determined by measuring the position of the limbing member <NUM>, with linear contact sensor <NUM>, and relating its position to the gliding surface <NUM>. The position of the limbing member <NUM> being related to the gliding surface <NUM>, and thereby a deviation D, through a conversion table which relates different positions of the limbing member <NUM> to different deviations D of a tree trunk <NUM> held in the harvesting head <NUM>.

The corrected thickness Tc is calculated by subtracting the deviation D from the measured thickness T.

It is realized by a person skilled in the art that features from various embodiments disclosed herein may be combined with one another in order to provide further alternative embodiments.

Instead of a pair of front limbing knives <NUM>, <NUM>, the tree trunk pressing device may be any other limbing knife <NUM>, <NUM>, <NUM>, <NUM>. It does not need to be a pair of limbing knives, it may be more than a pair or just one knife. It may also be one or several feed rollers <NUM>, <NUM>.

Instead of measuring the angular position of the front limbing knives <NUM>, <NUM> with an angle sensor it is possible to linearly measure their position with a linear sensor. This linear sensor could be coupled to pistons controlling the position of the limbing knives <NUM>, <NUM>.

The tree trunk pressing device may be a device separate from a limbing knife. The tree trunk pressing device may be anything as long as it presses the tree trunk in a direction towards a reference surface. A tree trunk surface follower may instead of a limbing member <NUM>, <NUM>' be a measuring wheel <NUM>.

The tree trunk surface follower may be a device separate from a limbing member or length measuring wheel.

A reference surface does not need to be a gliding surface, it could be a surface of any size, situated anywhere on the harvesting head as long as the tree trunk is pressed in a direction towards it and the position of a tree trunk pressing device and the position of a tree trunk surface follower is related to it.

It is possible to measure a thickness of a tree trunk <NUM> with the back limbing knives <NUM>, <NUM> in the same manner as done with the front limbing knives <NUM>, <NUM>.

Several thicknesses of the tree trunk may be determined at several points on the tree trunk <NUM> as it is fed through the harvesting head <NUM>, the points separated by a certain length interval, the interval may be <NUM> centimeters.

Instead of the linear contact sensor <NUM>, mechanically coupled to the limbing member <NUM> by connection <NUM>, it is possible to use a contact free linear sensor, which would not need the connection <NUM>. It is also possible to use an angle sensor positioned inside joint <NUM>, the angle sensor could be a rotary encoder or an analog angle sensor. If the tree trunk surface follower is a measuring wheel <NUM>, its position relative to the gliding surface <NUM> could be measured by a linear contact sensor coupled to the measuring wheel <NUM>. It could also be measured by a contact free linear sensor or by an angle sensor such as a rotary encoder or analog angle sensor.

A few alternatives to a tree trunk surface follower and devices pressing it towards a tree trunk surface has been disclosed. The devices can be combined with whichever tree trunk surface follower. For example, a measuring wheel could also be pressed towards the tree trunk surface by a compression spring or a torsion spring.

In the described method the deviation may also be determined by not only relating the position of the limbing member <NUM> to the gliding surface <NUM>, but also by relating the position of the limbing member <NUM> to the measured thickness T of the tree trunk <NUM>. The position of the limbing member <NUM> being related to the gliding surface <NUM>, and thereby a deviation D, through a conversion table which relates different positions of the limbing member <NUM> as well as different measured thicknesses T to different deviations D of a tree trunk <NUM> held in the harvesting head <NUM>.

Claim 1:
A method for determining a thickness of a tree trunk (<NUM>) in a harvesting head (<NUM>) for forestry, said harvesting head (<NUM>) comprising
a thickness measuring arrangement for measuring a measured thickness (T) of a tree trunk (<NUM>), said thickness measuring arrangement comprising a tree trunk pressing device (<NUM>, <NUM>, <NUM>, <NUM>), for pressing said tree trunk (<NUM>) in a direction towards a reference surface (<NUM>) of the harvesting head (<NUM>), and a first measuring sensor (<NUM>) arranged to measure the position of said tree trunk pressing device (<NUM>, <NUM>, <NUM>, <NUM>) relative to said reference surface (<NUM>), and
a deviation measuring arrangement, for measuring a deviation (D) of said tree trunk (<NUM>) from said reference surface (<NUM>),
said deviation measuring arrangement comprising a tree trunk surface follower (<NUM>, <NUM>; <NUM>') and a second measuring sensor (<NUM>) arranged to measure the position of said tree trunk surface follower (<NUM>, <NUM>; <NUM>'),
wherein the second measuring sensor is a proximity sensor,
wherein the tree trunk surface follower is a limbing member (<NUM>, <NUM>'), and wherein the limbing member (<NUM>, <NUM>') is curved,
said method comprising
pressing the tree trunk (<NUM>), with said tree trunk pressing device (<NUM>, <NUM>, <NUM>, <NUM>), in a direction towards the reference surface (<NUM>) of the harvesting head (<NUM>) and
determining a measured thickness (T) by measuring the position of the tree trunk pressing device (<NUM>, <NUM>, <NUM>, <NUM>) by means of the first measuring sensor (<NUM>) and relating said position to said reference surface (<NUM>),
wherein said method further comprises the steps of
determining a deviation (D) of the tree trunk (<NUM>) from said reference surface (<NUM>) by measuring a position of the curved limbing member (<NUM>, <NUM>') by means of the second measuring sensor (<NUM>) and relating said position of the curved limbing member (<NUM>, <NUM>') to said reference surface (<NUM>), and
calculating a corrected thickness (Tc) of the tree trunk (<NUM>) based on said measured thickness (T) and said deviation (D),
wherein determining the deviation (D) further comprises relating said position of the curved limbing member (<NUM>, <NUM>') to said measured thickness (T), and
determining the deviation (D) as a function of said position of the curved limbing member (<NUM>, <NUM>'), a curvature of the limbing member (<NUM>, <NUM>') and the measured thickness (T).