SE545347C2

SE545347C2 - Feeder unit and method for controlling a pair of support rollers of a feeder unit

Info

Publication number: SE545347C2
Application number: SE2250623A
Authority: SE
Inventors: Anton Nymark; Mats Ekberg
Original assignee: Usnr Ab
Priority date: 2022-05-25
Filing date: 2022-05-25
Publication date: 2023-07-11
Also published as: WO2023229509A1; SE2250623A1

Abstract

The present invention relates to a feeder unit and to a method for controlling such a feeder unit (4) that comprises a pair of support rollers configured to engage a timber body (2), wherein the feeder unit (4) comprises a hydraulic system having a first hydraulic piston assembly (13) connected to a first support roller (14) and a second hydraulic piston assembly (15) connected to a second support roller (16), and wherein the mutual distance between the pair of support rollers is adjustable by means of the hydraulic system. The method comprises the steps of abutting the pair of support rollers against the timber body (2), and exercising unguided mode of operation of the pair of support rollers, wherein the first hydraulic piston assembly (13) and the second hydraulic piston assembly (15) are in direct fluid communication with each other, wherein the method comprises the step of restricting the hydraulic liquid flow between the first hydraulic piston assembly (13) and the second hydraulic piston assembly (15), in order to provide a viscous dampening of any oscillating movements of the timber body (2).

Description

FEEDER UNIT AND METHOD FOR CONTROLLING A PAIR OF SUPPORT ROLLERS OF A FEEDER UNIT Technical field of the lnvention The present invention relates in general to a lumber processing line comprising one or more processing/cutting station(s) and a conveyer system, wherein individual timber bodies, such as logs or blocks/cants, are conveyed in the axial direction along the lumber processing line in order to be converted into smaller timber pieces, such as planks or boards.

At several locations along the lumber processing line, the lumber processing line com- prises feeder units configured for guiding and/or feeding the timber body when conveyed along the lumber processing line. The feeder units are especially configured to feed the timber body into and/or out of the processing station, and/or configured to guide/position the timber body during the machining/cutting performed in the processing station.

The present invention relates in particular to a feeder unit comprising a pair of support rollers configured to engage opposite sides of the timber body conveyed in the axial direction along the lumber processing line, wherein the feeder unit comprises a hydraulic system having a first hydraulic piston assembly connected to a first support roller of the pair of support rollers and configured to control the location of the first support and a second hydraulic piston assem- bly connected to a second support roller of the pair of support rollers and configured to control the location of the second support roller, and wherein the mutual distance between the pair of support rollers is adjustable in the transverse direction by means of the hydraulic system in or- der to match the width of the timber body.

The present invention also relates to a method for controlling a pair of support rollers of such a feeder unit.

Background of the lnvention All modern sawmill industry utilizes sawing lines, which often includes a large number of processing stations, the majority of which have a high level of automatization in order to obtain an optimal output, i.e. boards/timber pieces, from the raw material in the shape of round logs/timber bodies. Almost all timber bodies are curved in at least one plane. ln addition, it is a primary aim that the timber pieces sawn from a larger timber body present intended dimensions with minimum variations in each dimension category, as well as along each timber piece. lt is desirable to reduce the variations of dimension to a minimum, since such timber is assigned a high-quality category, thereby resulting in a maximal financial yield. The demands from the sawmill owner that every station along the sawing line shall gener- ate products having great dimensional accuracy are therefore exceptionally strict. A most frequently occurring demand is that the variation within a dimension category, regarding the thickness of the timber pieces, shall not be more than 0,5 millimeter.

When elucidating the dimensional accuracy of a band saw blade and the adjustment ac- curacy of a band saw machine carrying the saw blade, in the light of abovementioned precision demands, it is easily realized that the room for other guiding deficiencies in such a saw opera- tion is exceptionally small. ln other words, the smallest deviation of the timber body from the intended feeding path results in the risk of getting timber pieces with dimensions, which doesn't fall within the predefined limits.

The majority of the logs, which are passing through the sawmill, undergoes a number of operations before the heart piece of the log is finally divided, into a number of planks or boards, e.g. by means of band saw machines in a final dividing machine in the lumber processing line. The different processing stations of the lumber processing line may for instance be one or more chipper canter stations, one or more profile chipper stations, one or more sawing station. The timber bodies are conveyed along the lumber processing line using a transport/conveyer sys- tem, thereto each processing station comprises one or more feeder units configured to feed/guide the timber body during the machining/cutting performed in the processing station. The feeder unit may be located upstream and/or downstream the actual point of engagement between the timber body and the cutting tool, e.g. the teeth of a saw blade. Thereto the pro- cessing station as such may comprise support rollers that are in engagement with the timber body in close vicinity of the actual point of engagement between the timber body and the cut- ting tool. ln order to obtain a decent output from the raw material it is recommended that the timber body, i.e. the log, the block/cant, etc. is curve sawn during the dividing/cutting opera- tions as a consequence of that the logs in general are more or less curved in at least one plane. The radius of curvature is mostly from about 50 meters and up, wherein a straight timber body has infinite radius of curvature, which means that the bow height of a 4 meter long timber body may be as big as 40 millimeters. Curve sawing means that, during the dividing operation, the timber body is fed along a curve path which corresponds to the inherent curvature of the timber body.

However, when there are several feeder units cooperating with the processing station and/or the processing station comprises support rollers, there is a risk that the guiding/position- ing of the timber body is overdetermined during the cutting operation. Thus, there is a risk that feeder units and support rollers counteract each other, leading to poor output and to wear of the equipment.

One known way to handle such situations is for instance that the upstream located feeder unit is guiding and feeding the timber body towards the processing station, and when the cutting tool of the processing station engage the timber body the mode of operation of the feeder unit is switched to only feeding the timber body. Thereby the feeder unit becomes free- flowing in the transversal direction and follows the curvature of the timber body while still feed- ing the timber body in the axial direction into/through the processing station. Free-flowing mode of operation is also called unguided mode of operation.

Known feeder units having two modes of operation, fixed/guided and free-flowing/un- guided, are based on a mechanical linkage arrangement. Such feeder units comprise a pair of support rollers engaging the opposite sides of the timber body. A hydraulic piston assembly is connected to an arm holding the first support roller and to an arm holding the second support roller. The mutual distance between the pair of support rollers is adjustable in the transverse di- rection in order to match the width of the timber body, by means of the hydraulic piston assem- bly. When the support rollers are in engagement with the opposite sides of the timber body a mechanical linkage arrangement is switched between two modes. A fixed mode wherein the mechanical linkage arrangement is locked and thereby the location of the support rollers is fixed, and a free-flowing mode wherein mechanical linkage arrangement is un-locked and thereby the mutual distance of the support rollers is fixed but the location of the support rollers is free-flowing and follows the curvature of the timber body.

However, known systems take up a great deal of space due to the mechanical linkage arrangement and the manoeuvrability of such systems is limited. Thereby there is a risk of get- ting timber pieces with dimensions, which doesn't fall within the predefined limits. Thereto, many knows systems has a problem that during the free-flowing or unguided mode of opera- tion, when the timber body is grasped by support rollers for instance at the leading edge of the timber body, is that the remaining part of the timber body starts to oscillate rapidly. When the timber body oscillates, the timber pieces obtain wave-shaped surfaces and dimensions of the timber pieces may end up outside the predefined limits.

Thus, there is a need for a more compact and more accurate feeder unit that is config- ured to be operated in a free-flowing mode at the same time as oscillating timber body is pre- vented.

Obiect of the lnvention The present invention aims at obviating the aforementioned disadvantages and failings of previously known feeder units and method for controlling such feeder units, and at providing an improved feeder unit and method. A primary object of the present invention is to provide an improved feeder unit of the initially defined type wherein the feeder unit does not comprise a complex mechanical linkage arrangement to be able to perform a free-flowing mode of operation, i.e. to provide a feeder unit wherein the location of the support rollers is entirely con- trolled by a hydraulic system, at the same time as any oscillating movements of the timber body are dampened. lt is an object of the present invention is to provide an improved feeder unit of the initially defined type wherein a predetermined clamping pressure on the timber body, that is optimal for feeding the timber body without damaging the outer parts of the timber body, is achievable in both modes of operation and also when the dimensions of the timber body vary. lt is an object of the invention to provide a feeder unit that offers adequate guidance/feeding of the timber body during the complete machining/cutting operation. lt is also an object of the in- vention to provide a feeder unit that provides that the timber pieces obtain small dimensional variations within each dimensional category as well as along every individual timber piece.

Summary of the lnvention According to the invention at least the primary object is attained by means of the ini- tially defined feeder unit and method having the features defined in the independent claims. Preferred embodiments of the present invention are further defined in the dependent claims.

According to the present invention, there is provided a feeder unit of the initially de- fined type, which is characterized in that the hydraulic system comprises: - means for exerting a predetermined clamping pressure against the timber body by the pair of support rollers, and - controllable direct fluid communication connection between the first hydraulic piston assem- bly and the second hydraulic piston assembly, in order to make the location of the first support roller and the second support roller in relation to a centre line of the conveyer system follow any curvature of the timber body at the same time as the pair of support rollers exert the predetermined clamping pressure against the timber body, wherein the hydraulic system further comprises: - means for restricting the hydraulic liquid flow between the first hydraulic piston assembly and the second hydraulic piston assembly, in order to provide a viscous dampening of any oscillat- ing movements of the timber body.

According to the present invention, there is provided a method of the initially defined type, wherein the method comprises the steps of: - abutting the pair of support rollers against the timber body, wherein the pair of support rollers exert a predetermined clamping pressure against the timber body, and - exercising unguided mode of operation of the pair of support rollers, wherein the first hydrau- lic piston assembly and the second hydraulic piston assembly are in direct fluid communication with each other, in order to make the location of the first support roller and the second support roller in relation to a centre line of the conveyer system follow any curvature of the timber body at the same time as the pair of support rollers exert the predetermined clamping pressure against the timber body, wherein the method further comprises the step of: - restricting the hydraulic liquid flow between the first hydraulic piston assembly and the second hydraulic piston assembly, in order to provide a viscous dampening of any oscillating move- ments of the timber body.

Thus, the present invention is based on the insight of having one hydraulic piston assem- bly for each support roller, wherein the hydraulic system is arranged in such a way that the hy- draulic piston assemblies are either manoeuvred individually or together/concurrently. Thereby fixed/guided mode of operation and free-flowing/unguided mode of operation is made possible using a compact arrangement. Thereto, the hydraulic system comprises means for restricting the hydraulic liquid flow between the first hydraulic piston assembly and the second hydraulic piston assembly. Thereby the feeder unit admits the support rollers to follow the curvature of the timber body, i.e. slowly changing locations, at the same time as the feeder unit prevents the support rollers to follow oscillating movements of the timber body, i.e. rapidly changing loca- tions. Thus, when having perfect control of the location of the support rollers of the feeder unit during the entire timber body processing operation, the dimensional accuracy and quality of the timber pieces will be fulfilled. lt shall be pointed out that the present invention does not require that the feeder unit has to be able to be operated in a fixed mode of operation, i.e. the feeder unit may only have a single mode of operation, free-flowing.

According to various embodiments of the present invention, the first hydraulic piston assembly comprises a cylinder having a first chamber configured to displace the first support roller away from the centre line of the conveyer system when pressurized and a second cham- ber configured to displace the first support roller towards the centre line of the conveyer system when pressurized, and wherein the second hydraulic piston assembly comprises a cylinder hav- ing a first chamber configured to displace the second support roller away from the centre line of the conveyer system when pressurized and a second chamber configured to displace the second support roller towards the centre line of the conveyer system when pressurized. According to such various embodiments the step of exercising unguided mode of operation of the pair of sup- port rollers comprises the steps of: -connecting the second chamber of the first hydraulic piston assembly to the second chamber of the second hydraulic piston assembly, and connecting a constant pressure unit thereto, and - connecting the first chamber of the first hydraulic piston assembly to the first chamber of the second hydraulic piston assembly, and connecting a pressure sink of the hydraulic system thereto, whereby a predetermined abutting pressure is provided to the second chamber of the first hy- draulic piston assembly and to the second chamber of the second hydraulic piston assembly via the constant pressure unit in order to exert the predetermined clamping pressure against the timber body.

Thanks to the direct communication between the different chambers of the hydraulic piston assemblies, the support rollers will easily follow any curvature of the timber body, at the same time as the support roller is biased inwards striving to exert the predetermined clamping pressure, without having to know or control the location of the support roller in relation to the centre line of the conveyer system.

According to various embodiments of the present invention, the hydraulic liquid flow between the second chamber of the first hydraulic piston assembly and the second chamber of the second hydraulic piston assembly, is restricted.

The curvature of the timber body forces the second chamber of one of the hydraulic pis- ton assemblies to decrease, leading to a forced/pressed flow of liquid to the second chamber the other hydraulic piston assembly. Said preferred embodiment to restrict the hydraulic liquid flow between the second chamber of the first hydraulic piston assembly and the second cham- ber of the second hydraulic piston assembly is easier to control/predict, than having a restriction in a conduit having a sucked flow of liquid.

According to various embodiments of the present invention, the hydraulic liquid flow from the constant pressure unit to the second chamber of the first hydraulic piston assembly and to the second chamber of the second hydraulic piston assembly is unrestricted.

Thereby, if the timber body has somewhat varying thickness the predetermined clamp- ing pressure against the timber body is secured, also during curve sawing when the support roll ers are in the unguided mode of operation. According to various embodiments of the present invention, the method comprises the initial steps of: - pre-positioning of the pair of support rollers in relation to the centre line of the conveyer sys- tem before the leading edge of the timber body reaches the pair of support rollers in the axial direction, by means of the hydraulic system, wherein the mutual distance between the pair of support rollers in the pre-position is greater than the width of the timber body, and - abutting the pair of support rollers against the timber body after the leading edge of the tim- ber body has passed the pair of support rollers in the axial direction, by displacing at least the second support roller towards the centre line of the conveyer system until the pair of support rollers exerts the predetermined clamping pressure on the timber body.

Thereby the support rollers are protected from being rammed by the timber body.

According to various embodiments of the present invention, the hydraulic system com- prises a first servo valve and a second servo valve, wherein the pre-positioning of the pair of support rollers is performed by means of the first servo valve cooperating with the first hydrau- lic piston assembly and the second serve valve cooperating with the second hydraulic piston as- sembly. Thereby the location of each support roller is individually controlled, whereby the mu- tual distance between the support rollers and their position in relation to the centre line of the conveyer system is fully controllable and may be adapted to each individual timber body. The location of the individual support roller may also be further controlled based on the location of the other support roller.

Further advantages with and features of the invention will be apparent from the follow- ing detailed description of preferred embodiments.

Brief description of the drawings A more complete understanding of the abovementioned and other features and ad- vantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein: Fig. 1 is a schematic view from above of a machine for dividing a timber body into smaller timber pieces, wherein the machine comprises an inventive feeder unit, Fig. 2 is a schematic view from above of the machine according to figure 1, at the be- ginning of a timber body dividing operation, wherein the feeder unit is in the free-flowing mode of operation, Fig. 3 is a schematic view from the upstream direction of an inventive feeder unit, dur- ing pre-positioning of the pair of support rollers, Fig. 4 is a schematic view from the upstream direction of the inventive feeder unit ac- cording to figure 3, at the beginning of the abutting step, and Fig. 5 is a schematic view from the upstream direction of the inventive feeder unit ac- cording to figure 3, during the free-flowing mode of operation.

Detailed description of preferred embodiments of the lnvention The present invention belongs to the general technical field of lumber processing line comprising one or more processing/cutting station(s) and a conveyer system, wherein individual timber bodies (such as logs or blocks/cants), are conveyed in the axial direction along the lum- ber processing line in order to be converted into smaller timber pieces (such as planks or boards). The processing station of the lumber processing line may for instance be a chipper can- ter station, a profile chipper station, a sawing station, etc. Logs are fed into the loading end of the lumber processing line and boards leave the lumber processing line at the output end thereof.

Reference is initially made to figures 1 and 2, disclosing from above a machine, generally designated 1, configured for dividing a timber body 2 into smaller timber pieces 3, wherein the machine 1 comprises a feeder unit, generally designated 4. The present invention relates to such a feeder unit 4 and to a method for controlling such a feeder unit 4. The present invention will herein be described together with a sawing station, generally designated 5. However, the pre- sent invention is not limited to a specific type of processing station 5. The present invention also relates to a machine 1 comprising such a feeder unit 4 and a processing station The inventive machine 1 is suitable as a final dividing operation, wherein the heart piece of the log, also known as a four-sided block/cant, is divided into studs, planks and boards. How- ever, the inventive machine 1 may also be utilized more upstream in the lumber processing line, wherein the outer parts of the log are separated/removed in order to obtain boards as well as said four-sided cant/block, and/or in a canter/profile station. ln general, the disclosed machine 1 configured for dividing a timber body 2 into smaller timber pieces 3, comprises the feeder unit 4 and the sawing station 5, wherein the feeder unit 4 is located upstream the sawing station 5, seen in the feeding direction of the timber body 2. The disclosed sawing station 5 comprises four band saw machines having one endless saw band/blade each. The timber body 2 is divided into smaller timber pieces 3 by the saw blades as it is fed into/through the sawing station 5 by the feeder unit The machine 1 may also/instead comprise a downstream feeder/pulling unit (not dis- closed), configured to pull the smaller timber pieces 3 out of the processing station 5 and to feed the smaller timber pieces 3 towards the next station in the lumber processing line. Thus, the present invention is not limited to having the feeder unit 4 located upstream the processing station 5. The feeder unit 4 may also be located in isolation between two machines The sawing station 5 comprises a first/leading sawing unit, generally designated 6, and a second/trailing sawing unit, generally designated 7, wherein the second sawing unit 7 is located downstream the first sawing unit 6, seen in the feeding direction of the timber body 2. Accord- ing to various embodiments the sawing station 5 comprises only one sawing unit The first sawing unit 6 comprises a set of first saw b|ade(s) 8 and a pair of first support rollers 9 configured to cooperate with the set of first saw b|ade(s) 8. According to various em- bodiments, the set of first saw b|ade(s) 8 comprises one or two saw blades.

The second sawing unit 7 comprises a set of second saw b|ade(s) 10 and a pair of second support rollers 11 configured to cooperate with the set of second saw b|ade(s) 10. According to various embodiments, the set of second saw b|ade(s) 10 comprises one or two saw blades.

According to a conventional configuration of the sawing station 5, the set of first saw b|ade(s) 8 comprises two saw blades and the set of second saw b|ade(s) 10 comprises two saw blades, such that five smaller timber pieces 3 are obtained as output from the timber body di- viding operation. At least one of the saw blades of the set of first saw b|ade(s) 8 and the set of second saw b|ade(s) 10 may be displaced in the transverse direction and be located alongside the path of the timber body 2, i.e. in order not to engage the timber body 2 during the timber body dividing operation.

Possible horizontal rollers and/or conveyer belts/chains of the conveyer system are re- moved for the sake of clarity when reading figures 1 and The support rollers 9, 11 of the processing station 5 are rotatable around centre axes, and they may be driven or undriven or combinations thereof. The support rollers 9, 11 are con- figured to engage/abut the timber body 2 during the timber body processing/cutting operation, and are configured to control/guide the position of the timber body 2 during the timber body processing/cutting operation, such that the cutting tools engage the timber body at correct loca- tions and with great precision.

Each timber body 2 approaching the machine 1 has a so-called nominal or theoretical width. The nominal width of the individual timber body 2 approaching the machine 1 may be ob- tained/determined from the settings in an upstream processing station, i.e. intended output di- mensions from the upstream station. The nominal width is usually unique for each timber body 2 in a batch of timber bodies, i.e. may be different for different timber bodies 2. ln some situa- tions/operations the nominal width is predetermined and constant for an entire batch of timber bodies Each timber body 2 approaching the machine 1 also has a real width that is more or less constant along the entire length of the individual timber body 2, i.e. actual output dimensions generated in the upstream processing station. The real width is usually unique for each timber body 2 in a batch of timber bodies, i.e. may be different for different timber bodies 2. The real width of the individual timber body 2 approaching the machine 1 may be measured/determined upstream the sawing station 5 of the machine 1, i.e. before the timber body 2 is fed into the sawing station 5. The real width of the timber body 2 may be determined at the feeder unit 4 of the machine 1 by means of suitable sensors, settings, or the like.

Reference is now also made to figure 3. The feeder unit 4 comprises at least one pair of support rollers configured to engage opposite sides of the timber body 3 conveyed in the axial direction along the lumber processing line. The feeder unit 4 comprises a hydraulic system, gen- erally designated 12, having a first hydraulic piston assembly 13 connected to a first support roller 14 of the pair of support rollers and configured to control the location of the first support roller 14 and a second hydraulic piston assembly 15 connected to a second support roller 16 of the pair of support rollers and configured to control the location of the second support roller 16. The mutual distance between the pair of support rollers is adjustable in the transverse direction by means of the hydraulic system 12 in order to match the width of the timber body The support rollers 14 and 16 of the feeder unit 4 are rotatable around center axes, and one or both of them are driven in order to feed the timber body 2. The support rollers 14 and 16 are configured to engage/abut the timber body 2 and feed the timber body 2 in an axial direc- tion along the lumber processing line, while a power source, e.g. an electric motor (not shown), brings the support roller(s) to rotate. The feeder unit 4 may comprise a plurality of pairs of sup- port rollers, only one pair is disclosed in the figures. Any other pair of support rollers of the feeder unit 4 may be configured in line with the herein disclosed pair of support rollers of the feeder unit, or may be arranged in another way. The electric motor may be located inside or outside the driven support roller. The center axes of the pair of support rollers may be vertical, horizontal, or any other angle.

Reference is now made to figures 3-5 in order to describe the inventive method and the operation/control of the inventive feeder unit 4. ln figures 3-5, the conveyer system of the lum- ber processing line is illustrated by a horizontal roller 17, wherein the conveyer system has an imaginary center line illustrated by 18. During normal operation, the positioning of different ele- ments, such as support rollers, band saw machines, etc. is generally performed in relation to said imaginary center line 18 of the conveyer system.

Reference is made to figure 3. The disclosed hydraulic system 12 of the feeder unit 4 comprises means for pre-positioning of the pair of support rollers in relation to the centre line 18 of the conveyer system, wherein the mutual distance between the pair of support rollers in the pre-position is greater than the width of the timber body 2. The pre-positioning of the pair of support rollers in relation to the centre line 18 of the conveyer system is performed before the leading edge/end of the timber body 2 reaches the pair of support rollers in the axial direc tion. Thus, by means of the hydraulic system 12, before the timber body 2 reaches the pair of support rollers, the first support roller 14 and the second support roller 16 are positioned such that the timber body 2 may enter between them without hitting/ramming the support rollers,i.e. the mutual distance between the pair of support rollers in the pre-position is greater than the width of the timber body 2. The first support roller 14 and the second support roller 16 are in the pre-position located outside the intended path of the timber body 2. The mutual distance between the first support roller 14 and the second support roller 16 in the pre-position is equal to or more than 1 millimetre and equal to or less than 50 millimetres wider than the true width of the leading edge of the timber body 2, preferably equal to or more than 3 millimetres and equal to or less than 20 millimetres. A too wide pre-position entails that it takes too much time to engage the timber body 2 and a too narrow pre-position entails that the risk of having the timber body 2 hitting/ramming one of the support rollers increase.

According to various embodiments, the first hydraulic piston assembly 13 of the hydrau- lic system 12 comprises a cylinder 19 having a first chamber 20 configured to displace the first support roller 14 away from the centre line 18 of the conveyer system when pressurized and a second chamber 21 configured to displace the first support roller 14 towards the centre line 18 of the conveyer system when pressurized. ln the disclosed embodiment the first hydraulic piston assembly 13 comprises a piston disc 22 arranged in the cylinder 19 and separating the first chamber 20 and the second chamber 21 from each other. A piston rod 23 is connected to the piston disc 22 and is jointly displaced together with and by means of the piston disc 22. The pis- ton rod 23 extends through the end wall of the cylinder 19 and is connected to a holder 24, wherein the first support roller 14 is journaled in the holder 24. Thus, a displacement of the pis- ton disc 22 is transferred to the first support roller 14, and vice versa, via the piston rod 23. Ac- cording to various embodiments, the first chamber 20 of the cylinder 19 is located between the piston disc 22 and the first support roller 14, and the second chamber 21 is located on the oppo- site side of the piston disc 22, thereby the pressurized area of the piston disc 22 from the second chamber 21 is greater than the pressurized area of the piston disc 22 from the first chamber 20, due to the presence of the piston rod According to various embodiments, the first hydraulic piston assembly 13 comprises means for monitoring the location of the piston disc 22 in relation to the cylinder 19, and thereby indirectly monitoring the location of the first support roller 14 in relation to the centre line 18 of the conveyer system. Alternatively/additionally, the location of the first support roller 14 may be performed using other sensors, means, etc.

According to various embodiments, the second hydraulic piston assembly 15 of the hy- draulic system 12 comprises a cylinder 25 having a first chamber 26 configured to displace the second support roller 16 away from the centre line 18 of the conveyer system when pressurized and a second chamber 27 configured to displace the second support roller 16 towards the cen- tre line 18 of the conveyer system when pressurized. ln the disclosed embodiment the second hydraulic piston assembly 15 comprises a piston disc 28 arranged in the cylinder 25 andseparating the first chamber 26 and the second chamber 27 from each other. A piston rod 29 is connected to the piston disc 28 and is jointly displaced together with and by means of the piston disc 28. The piston rod 29 extends through the end wall of the cylinder 25 and is connected to a holder 30, wherein the second support roller 16 is journaled in the holder 30. Thus, a displace- ment of the piston disc 28 is transferred to the second support roller 16, and vice versa, via the piston rod 29. According to various embodiments, the first chamber 26 of the cylinder 25 is lo- cated between the piston disc 28 and the second support roller 16, and the second chamber 27 is located on the opposite side of the piston disc 28, thereby the pressurized area of the piston disc 28 from the second chamber 27 is greater than the pressurized area of the piston disc 25 from the first chamber 26, due to the presence of the piston rod According to various embodiments, the second hydraulic piston assembly 15 comprises means for monitoring the location of the piston disc 28 in relation to the cylinder 25, and thereby indirectly monitoring the location of the second support roller 16 in relation to the cen- tre line 18 of the conveyer system. Alternatively/additionally, the location of the second support roller 16 may be performed using other sensors, means, etc.

According to various embodiments, the means of the hydraulic system 12 for pre-posi- tion the pair of support rollers comprises a first servo valve 31 and a second servo valve 32, wherein first servo valve 31 cooperates with the first hydraulic piston assembly 13 and the sec- ond serve valve 32 cooperates with the second hydraulic piston assembly 15. The first servo valve 31 and the second servo valve 32 are individually connected to a pressure source HP, such as a fluid pump, and connected to a pressure sink LP, such as a reservoir/tank. The servo valves may be connected to different pressure sources/sinks, or the same pressure source/sink. One of the servo valves may be indirectly connected to the pressure source, in order to have reduced pressure.

The first support roller 14, and thereby the piston disc 22 of the first hydraulic piston as- sembly 13, has a current location and a target location. When the current location of the first support roller 14 is located too close to the centre line 18 of the conveyer system in relation to the target location, the first servo valve 31 is controlled to connect the pressure source HP to the first chamber 20 of the cylinder 19 and to connect the second chamber 21 of the cylinder 19 to the pressure sink LP. When the current location of the first support roller 14 is located too far away from the centre line 18 of the conveyer system in relation to the target location, the first servo valve 31 is controlled to connect the pressure source HP to the second chamber 21 of the cylinder 19 and to connect the first chamber 20 of the cylinder 19 to the pressure sink LP. The first servo valve 31 also has a neutral mode, wherein the first support roller 14 is not displaced, i.e. a fixed location of the first support rollerThe same applies to the pre-positioning of the second support roller 16, i.e. the second servo valve 32 cooperate with the second hydraulic piston assembly 15 in the corresponding way.

Thus, the first support roller 14 and the second support roller 16 are individually con- trolled to take their corresponding target location. Thereto, the target locations of the first sup- port roller 14 and the second support roller 16 are preferably determined in relation to each other in order to secure/obtain a mutual distance in the pre-position that is wider than the lead- ing edge of the timber body Reference is made to figure 4. The disclosed hydraulic system 12 of the feeder unit 4 comprises means for exerting a predetermined clamping pressure on the timber body 2 by the pair of support rollers, by abutting the first support roller 14 and the second support roller 16 against the timber body 2. The clamping pressure shall be big enough to be able to feed the tim- ber body 2 in the axial direction, but without causing permanent damage to the outer lay- ers/surfaces of the timber body 2 from the pair of support rollers. The clamping pressure may be adapted to the type of lumber/timber processed in the lumber processing line, i.e. a harder tim- ber may manage a higher clamping pressure.

Thus, by means of the hydraulic system 12, the abutting of the pair of support rollers against the timber body 2 is performed after the leading edge of the timber body 2 has passed the pair of support rollers in the axial direction, and the abutting is performed by displacing at least the second support roller 16 towards the centre line 18 of the conveyer system until the pair of support rollers exerts the predetermined clamping pressure on the timber body According to various embodiments of the abutting step, after the leading edge of the timber body 2 has passed the first and the second support rollers 14, 16 in the axial direction, the first support roller 14 is displaced inwards from the above mentioned target location, lo- cated outside the path of the timber body 2, to a final location located for instance at half the theoretical width of the timber body 2 offset from the centre line 18 of the conveyer system, by means of the first servo valve 31. According to alternative embodiments the above mentioned target location of the first support roller 14 is equal to the above mentioned final location of the first support roller 14, i.e. no displacement of the first support roller 14 when going from the pre-positioning step to the abutting step.

Thereafter the second support roller 16 is displaced towards the centre line 18 of the conveyer system until the pair of support rollers exerts the predetermined clamping pressure on the timber body The displacement of the second support roller 16 towards the centre line 18 of the con- veyer system during the abutting step comprises the steps of: - disconnecting the second servo valve 32 from the second hydraulic piston assembly 15,- connecting a constant pressure unit 33 to the second chamber 27 of the second hy- draulic piston assembly 15, wherein a predetermined abutting pressure is provided to the sec- ond chamber 27 of the second hydraulic piston assembly 15, and - connecting the first chamber 26 of the second hydraulic piston assembly 15 to a pres- sure sink (LP) of the hydraulic system According to various embodiments, the disconnection of the second servo valve 32 is performed by means of a first controllable valve 34 closing/removing the communication be- tween the second servo valve 32 and the second hydraulic piston assembly 15. The connection of the second hydraulic piston assembly 15 to the constant pressure unit 33 and to the pressure sink LP, respectively, is performed by means of a second controllable valve 35. lt shall be pointed out that the first controllable valve 34 and the second controllable valve 35 may be arranged in a single valve unit or be constituted by several valve units. For instance, the first chamber 26 of the second hydraulic piston assembly 15 may have only one connection, instead of two connec- tions as disclosed in the figures, thereby one valve unit is configured to disconnect the second servo valve 32 and connect the pressure sink (LP) concurrently. Correspondingly, the second chamber 27 of the second hydraulic piston assembly 15 may have only one connection, instead of two connections as disclosed in the figures, thereby one valve unit is configured to disconnect the second servo valve 32 and connect the constant pressure unit 33 concurrently.

As a consequence of having the second chamber 27 of the second hydraulic piston as- sembly 15 connected to the constant pressure unit 33 and having the first chamber 26 of the second hydraulic piston assembly 15 connected to the pressure sink (LP), the second support roller 16 will be biased inwards under the action of the predetermined abutting pressure pro- vided via the constant pressure unit The constant pressure unit 33 is connected to a pressure source (HP) and to a pressure sink (LP), wherein the output pressure level is somewhere in-between the pressure level of the pressure source (HP) and the pressure sink (LP). The output pressure of the constant pressure unit 33 is preferably adjustable. The function of the constant pressure unit 33 is to add hydraulic fluid should the pressure drop below a predetermined level and release/empty hydraulic fluid should the pressure increase above a predetermined level. Thus, the output pressure level is maintained within an acceptable range. The pressure source and the pressure sink may be the same as connected to the servo valves.

According to various embodiments of the abutting step, the first hydraulic piston assem- bly 13 is kept connected to the first servo valve 31, wherein the first support roller 14 is kept at a fixed location in the transverse direction by means of the first servo valve 31, i.e. at the above mentioned final location of the first support roller 14. Since the second support roller 16 is bi- ased inwards by the predetermined abutting pressure, the clamping pressure is constant even though the true width of the timber body 2 varies, and the location of the timber body 2 is de- fined/determined by the location of the first support roller 14. Thereby the first support roller is fixed and the second support roller is biased towards the fixed first support roller, together ex- erting the predetermined clamping pressure against the timber body. At the same time the loca- tion of the first side/surface of the timber body, i.e. the side that is in engagement with the first support roller, is known. When the first support roller remains in the fixed location, the feeder unit operate in the fixed mode of operation.

According to various embodiments of the abutting step, also the first support roller 14 is displaced towards the centre line 18 of the conveyer system, wherein the displacement com- prises the steps of: - disconnecting the first servo valve 31 from the first hydraulic piston assembly 13, - connecting the constant pressure unit 33 to the second chamber 21 of the first hydrau- lic piston assembly 13, wherein the predetermined abutting pressure is provided to the second chamber 21 of the first hydraulic piston assembly 13, and - connecting the first chamber 20 of the first hydraulic piston assembly 13 to the pres- sure sink (LP) of the hydraulic system According to various embodiments, the disconnection of the first servo valve 31 is per- formed by means of a third controllable valve 36 closing/removing the communication between the first servo valve 31 and the first hydraulic piston assembly 13. The connection of the first hy- draulic piston assembly 13 to the constant pressure unit 33 and to the pressure sink LP, respec- tively, is performed by means of a fourth controllable valve 37. lt shall be pointed out that the third controllable valve 36 and the fourth controllable valve 37 may be arranged in a single valve unit or be constituted by several valve units. For instance, the first chamber 20 of the first hy- draulic piston assembly 13 may have only one connection, instead of two connections as dis- closed in the figures, thereby one valve unit is configured to disconnect the first servo valve 31 and connect the pressure sink (LP) concurrently. Correspondingly, the second chamber 21 of the first hydraulic piston assembly 13 may have only one connection, instead of two connections as disclosed in the figures, thereby one valve unit is configured to disconnect the first servo valve 31 and connect the constant pressure unit 33 concurrently.

As a consequence of having the second chamber 21 of the first hydraulic piston assem- bly 13 connected to the constant pressure unit 33 and having the first chamber 20 of the first hydraulic piston assembly 13 connected to the pressure sink (LP), the first support roller 14 will be biased inwards under the action of the predetermined abutting pressure provided by the constant pressure unit 33. Since the first support roller 14 and the second support roller 16 are both biased inwards by the predetermined abutting pressure, the clamping pressure is constanteven though the true width of the timber body 2 varies, but the location of the timber body 2 is not defined/determined, i.e. unguided mode of operation.

When exercising unguided mode of operation of the pair of support rollers, the first hy- draulic piston assembly 13 and the second hydraulic piston assembly 15 are in direct fluid com- munication with each other, whereby the location of the pair of support rollers in relation to a centre line 18 of the conveyer system follows any curvature of the timber body 2 at the same time as the pair of support rollers exerts the predetermined clamping pressure on the timber body 2. See figure 5. The unguided mode of operation may be performed after the abutting step and/or concurrently with the termination of the abutting step. ln addition to unguided mode of operation, the method comprises the step of restricting the hydraulic liquid flow between the first hydraulic piston assembly 13 and the second hydrau- lic piston assembly 15, in order to provide a viscous dampening of any oscillating movements of the timber body 2. Thus, at the same time as the support rollers follows any curvature of the timber body 2, the support rollers do not follow oscillating movements, i.e. rapidly sway- ing/swinging movements, but dampens the oscillating movements. Thus, the hydraulic system 12 comprises means for restricting the hydraulic liquid flow between the first hydraulic piston assembly 13 and the second hydraulic piston assembly 15, in order to provide a viscous dampen- ing of any oscillating movements of the timber body 2 when the support rollers are configured to follow any curvature of the timber body The step of exercising unguided mode of operation of the pair of support rollers com- prises preferably the steps of connecting the second chamber 21 of the first hydraulic piston as- sembly 13 to the second chamber 27 of the second hydraulic piston assembly 15, and connect- ing the constant pressure unit 33 thereto, and connecting the first chamber 20 of the first hy- draulic piston assembly 13 to the first chamber 26 of the second hydraulic piston assembly 15, and connecting the pressure sink of the hydraulic system 12 thereto, whereby a predetermined abutting pressure is provided to the second chamber 21 of the first hydraulic piston assembly 13 and to the second chamber 27 of the second hydraulic piston assembly 15 via the constant pres- sure unit 33 in order to exert the predetermined clamping pressure against the timber body Thus, the hydraulic system 12 comprises controllable direct fluid communication con- nection/conduit between the second chamber 21 of the first hydraulic piston assembly 13 and the second chamber 27 of the second hydraulic piston assembly 15, wherein the constant pres- sure unit 33 is connected to said connection, and controllable direct fluid communication con- nection/conduit between the first chamber 20 of the first hydraulic piston assembly 13 and the first chamber 26 of the second hydraulic piston assembly 15, wherein the pressure sink of the hydraulic system 12 is connected to said connection, whereby a predetermined abutting pres- sure is provided to the second chamber 21 of the first hydraulic piston assembly 13 and to thesecond chamber 27 of the second hydraulic piston assembly 15 via the constant pressure unit 33 in order to exert the predetermined clamping pressure against the timber body The means for restricting the hydraulic liquid flow between the first hydraulic piston as- sembly 13 and the second hydraulic piston assembly 15 is constituted by a restriction valve as- sembly 38. The restriction valve assembly 38 is preferably located at the controllable direct fluid communication connection/conduit between the second chamber 21 of the first hydraulic pis- ton assembly 13 and the second chamber 27 of the second hydraulic piston assembly 15. The restriction valve assembly 38 may be located at the controllable direct fluid communication con- nection/conduit between the first chamber 20 of the first hydraulic piston assembly 13 and the first chamber 26 of the second hydraulic piston assembly 15. The degree of restriction is prefera- bly controllable/adjustable. The degree of restriction shall not be too high in order not to have negative effect on the ability of the support rollers to follow the curvature of the timber body 2, and not be too low in order to be able to dampen oscillating movements of the timber body ln the disclosed embodiments the restriction valve assembly comprises a first restriction valve member 38a that is configured to restrict the flow of liquid moving from the second cham- ber 27 of the second hydraulic piston assembly 15 towards the second chamber 21 of the first hydraulic piston assembly 13, at the same time as a movement of liquid from the second cham- ber 21 of the first hydraulic piston assembly 13 towards the second cham ber 27 of the second hydraulic piston assembly 15. ln order to fulfil such function, the first restriction valve member 38a comprises two parallel branches wherein one branch comprises a non-return valve and one branch comprises a restriction. ln the disclosed embodiments the restriction valve assembly comprises a second re- striction valve member 38b that is configured to restrict the flow of liquid moving from the sec- ond chamber 21 of the first hydraulic piston assembly 13 towards the second chamber 27 of the second hydraulic piston assembly 15, at the same time as a movement of liquid from the second chamber 27 of the second hydraulic piston assembly 15 towards the second chamber 21 of the first hydraulic piston assembly 13. ln order to fulfil such function, the second restriction valve member 38b comprises two parallel branches wherein one branch comprises a non-return valve and one branch comprises a restriction. ln the disclosed embodiments the constant pressure unit 33 is connected to the control- lable direct fluid communication connection/conduit between the second chamber 21 of the first hydraulic piston assembly 13 and the second chamber 27 of the second hydraulic piston as- sembly 15 in such a way that the constant pressure is unrestricted provided to the second cham- bers of the hydraulic piston assemblies. Thus, the constant pressure unit 33 is connected to the second chamber 21 of the first hydraulic piston assembly 13 intermediate the restriction valve assembly 38 and the second chamber 21 of the first hydraulic piston assembly 13, and to thesecond chamber 27 of the second hydraulic piston assembly 15 intermediate the restriction valve assembly 38 and the second chamber 27 of the second hydraulic piston assembly According to the embodiments wherein the first support roller 14 is biased inwards dur- ing the abutting step, the unguided mode of operation of the pair of support rollers is entered by setting/putting the first hydraulic piston assembly 13 and the second hydraulic piston assem- bly 15 in fluid communication with each other.

According to the embodiments wherein the first support roller 14 has a fixed/final loca- tion during the abutting step, the unguided mode of operation of the pair of support rollers is initialised by performing the steps of disconnecting the first servo valve 31 from the first hydrau- lic piston assembly 13, connecting the constant pressure unit 33 to the second chamber 21 of the first hydraulic piston assembly 13, wherein the predetermined abutting pressure is provided to the second chamber 21 of the first hydraulic piston assembly 13, connecting the first chamber 20 of the first hydraulic piston assembly 13 to the pressure sink (LP) of the hydraulic system 12, and putting the first hydraulic piston assembly 13 and the second hydraulic piston assembly 15 in direct fluid communication with each other.

Thus, in the disclosed embodiments the second controllable valve 35 and the fourth controllable valve 37 together control the direct fluid communication between the first hydrau- lic piston assembly 13 and the second hydraulic piston assembly 15, at the same time as the first servo valve 31 and the second servo valve 32 are disconnected.

Thus, both the first support roller 14 and the second support roller 16 are biased in- wards exerting the predetermined clamping pressure on the timber body 2, at the same time as the pair of support rollers is free-flowing and follows the curvature of the timber body 2. When the curvature of the timber body 2 pushes/displaces the first support roller 14 outwards, the hy- draulic fluid from the second chamber 21 of the first hydraulic piston assembly 13 is transferred to the second chamber 27 of the second hydraulic piston assembly 15, and the hydraulic fluid in the first chamber 26 of the second hydraulic piston assembly 15 is transferred to the first cham- ber 20 of the first hydraulic piston assembly By having the constant pressure unit 33 and the pressure sink (LP) connected to the first hydraulic piston assembly 13 and to the second hydraulic piston assembly 15 also during the un- guided mode of operation, a variation in true width of a specific timber body 2 is handled such that the predetermined clamping pressure on the timber body 2 is secured. Thus, should the true width of the timber body 2 decrease the constant pressure unit 33 will add hydraulic fluid to the second chambers 21, 27 of the first and second hydraulic piston assemblies 13, 15 and hy- draulic fluid will be emptied/removed from the first chambers 20, 26 of the first and second hy- draulic piston assemblies 13, 15. Should the true width of the timber body 2 increase the con- stant pressure unit 33 will remove/empty hydraulic fluid from the second chambers 21, 27 ofthe first and second hydraulic piston assemblies 13, 15 and hydraulic fluid will be added to the first chambers 20, 26 of the first and second hydraulic piston assemblies 13, lt shall be pointed out that by means of the hydraulic system 12, one may alternate be- tween the unguided mode of operation of the pair of support rollers (figure 5) and a guided mode of operation of the pair of support rollers (figure 4). ln the guided mode of operation, the first support roller 14 or the second support roller 16 is fixed by having the corresponding servo valve 31, 32 reconnected and by terminating the direct fluid communication between the first and second hydraulic piston assemblies 13, 15. The guided mode of operation may be applied after the abutting step and until the timber body 2 has reached the support rollers of the pro- cessing station 5, or until the timber pieces 3 have reached a downstream feeder unit.

The guided mode of operation may also be entered when a maximum transversal dis- placement in relation to the centre line 18 of the conveyer system, of any of the first and second support rollers 14, 16 is reached. Limitation of the maximum transversal displacement may also be accomplished by a mechanical stop associated with the hydraulic piston assemblies and/or the holders supporting the support rollers.

Feasible modifications of the lnvention The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, and the present invention is consequently defined by the wording of the appended claims and the equivalents thereof and the equipment can be modified in all conceivable ways within the scope of the appended claims. lt shall also be pointed out that all information about/concerning terms such as above, under, upper, lower, etc., shall be interpreted/read having the equipment oriented according to the figures, having the drawings oriented such that the references can be properly read. Thus, such terms only indicates mutual relations in the shown em bodiments, which relations may be changed if the inventive equipment is provided with another structure/design. lt shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combina- tion shall be considered/regarded obvious, when the combination is possible.

Claims

1. Method for controlling a pair of support rollers of a feeder unit (4) for a lumber processing |ine, wherein the lumber processing line comprises one or more processing station(s) (5) and a conveyer system, wherein the pair of support rollers are configured to engage opposite sides of a timber body (2) conveyed in the axial direction along the lumber processing line, and wherein the mutual distance between the pair of support rollers is adjustable in the transverse direction by means of a hydraulic system (12) in order to match the width of the timber body (2), a first hydraulic piston assembly (13) of said hydraulic system (12) being configured to control the loca- tion of a first support roller (14) of said pair of support rollers and a second hydraulic piston as- sembly (15) of said hydraulic system (12) being configured to control the location of a second support roller (16) of said pair of support rollers, the method comprising the steps of: - abutting the pair of support rollers against the timber body (2), wherein the pair of support rollers exert a predetermined clamping pressure against the timber body (2), and - exercising unguided mode of operation of the pair of support rollers, wherein the first hydrau- lic piston assembly (13) and the second hydraulic piston assembly (15) are in direct fluid com- munication with each other, in order to make the location of the first support roller (14) and the second support roller (16) in relation to a centre |ine (18) of the conveyer system follow any curvature of the timber body (2) at the same time as the pair of support rollers exert the predetermined clamping pressure against the timber body (2), wherein the method further comprises the step of: - restricting the hydraulic liquid flow between the first hydraulic piston assembly (13) and the second hydraulic piston assembly (15), in order to provide a viscous dampening of any oscillat- ing movements of the timber body (2).

2. The method according to claim 1, wherein the first hydraulic piston assembly (13) comprises a cylinder (19) having a first chamber (20) configured to displace the first support roller (14) away from the centre line (18) of the conveyer system when pressurized and a second chamber (21) configured to displace the first support roller (14) towards the centre line (18) of the conveyer system when pressurized, and wherein the second hydraulic piston assembly (15) comprises a cylinder (25) having a first chamber (26) configured to displace the second support roller (16) away from the centre line of the conveyer system when pressurized and a second chamber (27) configured to displace the second support roller (16) towards the centre line of the conveyersystem when pressurized, wherein the step of exercising unguided mode of operation of the pair of support rollers comprises the steps of: -connecting the second chamber (21) of the first hydraulic piston assembly (13) to the second chamber (27) of the second hydraulic piston assembly (15), and connecting a constant pres- sure unit (33) thereto, and - connecting the first chamber (20) of the first hydraulic piston assembly (13) to the first cham- ber (26) of the second hydraulic piston assembly (15), and connecting a pressure sink of the hydraulic system (12) thereto, whereby a predetermined abutting pressure is provided to the second chamber (21) of the first hydraulic piston assembly (13) and to the second chamber (27) of the second hydraulic piston assembly (15) via the constant pressure unit (33) in order to exert the predetermined clamping pressure against the timber body (2).

3. The method according to claim 2, wherein the hydraulic liquid flow between the second chamber (21) of the first hydraulic piston assembly (13) and the second chamber (27) of the sec- ond hydraulic piston assembly (15), is restricted.

4. The method according to claim 2 or 3, wherein the hydraulic liquid flow from the constant pressure unit (33) to the second chamber (21) of the first hydraulic piston assembly (13) and to the second chamber (27) of the second hydraulic piston assembly (15) is unrestricted.

5. The method according to any preceding claim, wherein the method comprises the initial steps of: - pre-positioning of the pair of support rollers in relation to the centre line of the conveyer sys- tem before the leading edge of the timber body (2) reaches the pair of support rollers in the axial direction, by means of the hydraulic system (12), wherein the mutual distance between the pair of support rollers in the pre-position is greater than the width of the timber body (2), and - abutting the pair of support rollers against the timber body (2) after the leading edge of the timber body (2) has passed the pair of support rollers in the axial direction, by displacing at least the second support roller (16) towards the centre line of the conveyer system until the pair of support rollers exerts the predetermined clamping pressure on the timber body (2).

6. The method according to claim 5, wherein the hydraulic system (12) comprises a first servo valve (31) and a second servo valve (32), wherein the pre-positioning of the pair of support roll- ers is performed by means of the first servo valve (31) cooperating with the first hydraulic pistonassembly (13) and the second serve valve (32) cooperating with the second hydraulic piston as- sembly (15).

7. Feeder unit (4) suitable for a lumber processing line that comprises one or more processing station(s) (5) and a conveyer system, the feeder unit (4) comprising a pair of support rollers con- figured to engage opposite sides of a timber body (2) conveyed in the axial direction along the lumber processing line, wherein the feeder unit (4) comprises a hydraulic system (12) having a first hydraulic piston assembly (13) connected to a first support roller (14) of the pair of support rollers and configured to control the location of the first support roller (14) and a second hy- draulic piston assembly (15) connected to a second support roller (16) of the pair of support roll- ers and configured to control the location of the second support roller (16), and wherein the mutual distance between the pair of support rollers is adjustable in the transverse direction by means of the hydraulic system (12) in order to match the width of the timber body (2), the feeder unit () being characterized in that the hydraulic system (12) comprises: - means for exerting a predetermined clamping pressure against the timber body (2) by the pair of support rollers, and - controllable direct fluid communication connection between the first hydraulic piston assem- bly (13) and the second hydraulic piston assembly (15), in order to make the location of the first support roller (14) and the second support roller (16) in relation to a centre line (18) of the conveyer system follow any curvature of the timber body (2) at the same time as the pair of support rollers exert the predetermined clamping pressure against the timber body (2), wherein the hydraulic system (12) further comprises: - means for restricting the hydraulic liquid flow between the first hydraulic piston assembly (13) and the second hydraulic piston assembly (15), in order to provide a viscous dampening of any oscillating movements of the timber body (2).

8. The feeder unit (4) according to claim 7, wherein the first hydraulic piston assembly (13) com- prises a cylinder (19) having a first chamber (20) configured to displace the first support roller (14) away from the centre line (18) of the conveyer system when pressurized and a second chamber (21) configured to displace the first support roller (14) towards the centre line of the conveyer system when pressurized, and wherein the second hydraulic piston assembly (15) comprises a cylinder (25) having a first chamber (26) configured to displace the second support roller (16) away from the centre line (18) of the conveyer system when pressurized and a second chamber (27) configured to displace the second support roller (16) towards the centre line of the conveyer system when pressurized, wherein the hydraulic system (12) comprises:- controllable direct fluid communication connection between the second chamber (21) of the first hydraulic piston assembly (13) and the second chamber (27) of the second hydraulic pis- ton assembly (15), wherein a constant pressure unit (33) is connected to said connection, and - controllable direct fluid communication connection between the first chamber (20) of the first hydraulic piston assembly (13) and the first chamber (26) of the second hydraulic piston as- sembly (15), wherein a pressure sink of the hydraulic system (12) is connected to said connec- tion, whereby a predetermined abutting pressure is provided to the second chamber (21) of the first hydraulic piston assembly (13) and to the second chamber (27) of the second hydraulic piston assembly (15) via the constant pressure unit (33) in order to exert the predetermined clamping pressure against the timber body (2).

9. The feeder unit (4) according to claim 8, wherein the controlla ble direct fluid communication connection between the second chamber (21) of the first hydraulic piston assembly (13) and the second chamber (27) of the second hydraulic piston assembly (15) comprises a restriction valve assembly (38a, 38b).

10. The feeder unit (4) according to claim 9, wherein the constant pressure unit (33) is con- nected to the second chamber (21) of the first hydraulic piston assembly (13) intermediate the restriction valve assembly (38) and the second chamber (21) of the first hydraulic piston assem- bly (13), and to the second chamber (27) of the second hydraulic piston assembly (15) interme- diate the restriction valve assembly (38) and the second chamber (27) of the second hydraulic piston assembly (15).

11. The feeder unit (4) according to any of claims 7-10, wherein the hydraulic system (12) fur- ther comprises: - means for pre-positioning of the pair of support rollers in relation to a centre line of the con- veyer system, wherein the mutual distance between the pair of support rollers in the pre-posi- tion is greater than the width of the timber body (2).

12. The feeder unit (4) according to claim 11, wherein the means for pre-positioning of the pair of support rollers comprises a first servo valve (31) and a second servo valve (32), wherein the pre-positioning of the pair of support rollers is performed by means of the first servo valve (31) configured to cooperate with the first hydraulic piston assembly (13) and the second serve valve (32) configured to cooperate with the second hydraulic piston assembly (15).