Title:
Method and Apparatus For Manufactring a Nail Plate Truss Without Setting
Kind Code:
A1


Abstract:
A method and an apparatus for the manufacture of a nail plate truss (2) without setting, said nail plate truss including first-side nail plates (3) of the truss, second-side nail plates (3) of the nail plate truss, and struts (4) joined together by nail plates. According to the inventive method, the structure of the truss is stored in an electric control system (20), and the nail plates (3) and struts (4) for a truss are brought into their positions required by the truss structure onto a horizontal assembly table (5), as controlled by an electric control system, using handling members (11) separate from the assembly table, the parts (3, 4) of the truss being positioned into their positions based directly on positioning of the handling member (11) transporting them.



Inventors:
Nuutinen, Arvo (Kokkola, FI)
Application Number:
11/918926
Publication Date:
12/25/2008
Filing Date:
04/18/2006
Primary Class:
Other Classes:
414/222.02
International Classes:
E04B1/00; B27F7/15; B65H1/00; E04C3/17; B27F
View Patent Images:



Primary Examiner:
ARBES, CARL J
Attorney, Agent or Firm:
FAY SHARPE LLP (Cleveland, OH, US)
Claims:
1. A method for manufacturing a nail plate truss (2) without setting, said nail plate truss including first-side nail plates (3) of the truss, second-side nail plates (4) of the truss and struts (4) joined together by means of the nail plates, characterised in that the structure of the truss (2) is stored in an electrical control system (20), as controlled by an electrical control system, the nail plates (3) and the struts (4) for the truss are transported to their positions on the horizontal assembly table, required by the truss structure, using handling members (11) separate from the assembly table, and that the parts (3, 4) of the truss are positioned directly based on positioning of the handling members (11) transporting them.

2. A method according to claim 1, characterised in that, as controlled by the electric control system (20): the first-side nail plates (3) of the truss (2) are fetched from their pick-up positions (19) and, above the assembly table (5), are brought into their positions at the node joints of the truss onto the assembly table and, are fastened to the assembly table with the nail portions directed upwardly, the struts (4) for the truss (2) are fetched from their pick-up positions (19) and, above the assembly table (5), are brought into their positions above the first-side nail plates (3) of the truss present on the assembly table and, are pressed against the nail plates by the handling members (11), the second-side nail plates (3) of the truss (2) are fetched from their pick-up positions (19) and above the assembly table (5), are brought into their positions at the node joints of the truss above the struts (4) present on the assembly table, the nail portions downwardly directed, and are pressed against the struts by the handling members (11), and fastening the first-side nail plates (3) of the nail plate truss (2) to the assembly table (5) is released, and the truss is removed from the assembly table.

3. A method according to claim 1, characterised in that, the node joints of the truss (3) removed from the assembly table are tightened to final strength by pressing the nail plates (3) into the struts (4) over the entire length of their nail portions.

4. A method according to claim 1, characterised in that, the assembly table (5) is magnetised in the area of the node joints for fastening the first-side nail plates (3) of the nail plate truss (2) to the assembly table.

5. A method according to claim 1, characterised in that, while bringing the strut (4a) into its position, the vertical surface thereof is horizontally contacted with the vertical surface of another strut (4b), and the strut is then vertically pressed against the nail plate (3).

6. A method according to claim 1 characterised in that, the strut (4) is pressed against the first-side nail plates (3) by one handling member (11) at each node joint.

7. An apparatus (1) for manufacturing the nail plate truss (2) without setting, said nail plate truss including first-side nail plates (3) of the truss, second-side nail plates (3) of the truss, and struts (4) joined together by the nail plates, characterised in that the apparatus includes en electrical control system (20) in which the structure of the nail plate truss (2) can be stored, a horizontal, fixed and continuous assembly table (5), fastening means controllable by the electrical control system, for fastening the first-side nail plates (3) to the assembly table (5), handling members (11) controllable by the electrical control system, separate from the assembly table (5) and supported thereabove, comprising gripping means (13) for gripping a nail plate and a strut and holding them, as well as pressing means (14, 15) for pressing the struts and nail plates against each other, and transfer means (10, 12) controllable by the electrical control system, for moving the handling members (11) above the assembly table and positioning thereof.

8. An apparatus (1) according to claim 7, characterised in that, the fastening means are magnetising means (9) for magnetising the assembly table (5).

9. An apparatus (1) according to claim 7, characterised in that, the gripping means comprise opposite gripping members (13) movable relative to each other, for gripping a nail plate (3) or a strut (4) by clamping it between the gripping members.

10. An apparatus (1) according to claim 7, characterised in that, the gripping means comprise negative pressure means (21) for gripping the strut (4) by means of negative pressure.

11. An apparatus (1) according to claim 7, characterised in that, the gripping means comprise magnetic members (21) for gripping the nail plates (3).

12. An apparatus (1) according to claim 7, characterised in that, the pressing means comprise a support surface (14) and a drive (15) for pressing the support surface towards the assembly table (5) in order to press the nail plate (3) and the strut (4) against each other.

13. An apparatus (1) according to claim 7, characterised in that, the transfer means comprise first linear guides (10) above the assembly table, parallel to the assembly table (5), carrying the handling members (11) for transferring the handling members therealong, second linear guides (12) supported above the assembly table, carrying the first linear guides (10), arranged perpendicularly thereto, parallel to the assembly table, for transferring the first linear guides along the second linear guides, and drive means (16) for realising the above-mentioned movements along the linear guides (10, 12).

14. An apparatus (1) according to claim 7, characterised in that, for each handling member (11), the transfer means comprise a lifting device (17) for transferring the handling member in a direction perpendicular to the assembly table (5).

15. An apparatus (1) according to claim 7, characterised in that, for each handling member (11), the transfer means comprise a rotational device (18) for rotating the handling member about its vertical axis.

Description:

TECHNICAL FIELD

The invention refers to a method defined in the preamble of claim 1 for the manufacture of a nail plate truss. According to the preamble of claim 7, the invention also relates to an apparatus for manufacturing the nail plate truss.

BACKGROUND OF THE INVENTION

The manufacture of roof trusses and other corresponding nail plate trusses usually used in construction includes different steps of work. Wooden struts for the truss, cut to size and machined to have desired form, are traditionally laid on the assembly table in an order required by the final structure, and in contact with each other. Subsequently, the parts are joined together by nail plates pressed into their upper surface, connecting the parts together. Next, the nail plate truss is turned upside down for connecting the nail plates to the node joints of the struts on the other side of the truss, too.

In its traditional form, the manufacturing method described requires a lot of handwork, and is relatively slow. The parts are laid on the assembly table typically manually. Positioning of the parts must be done dimensionally accurately which requires special carefulness. In order to speed up setting, and to improve accuracy, among others, different stops have been developed, moving in grooves arranged in the assembly table, defining the locations for parts of the truss, against which the parts are laid. In patent specification CA2464573, for example, a positioner is disclosed which, in addition to defining the positions for parts of the truss, also presses the parts against each other for strengthening the joint. In U.S. Pat. No. 6,702,269, members movable in grooves of the assembly table are disclosed for supporting parts of the truss at their proper positions. Moreover, U.S. Pat. No. 6,712,347 relates to an improved system of automatically movable stops, in which moving parts has been tried to protect against dust and material dislodged from wooden parts. Laying of parts of the truss parts is facilitated and accelerated by different stops and retainers forming a setting on the assembly table, defining the positions for parts of the truss. On the other hand, changing the truss type requires a time-consuming change of setting. Changing the setting can be speeded up to some extent by stops positioned by an automatic control. Mechanical parts and grooves of the assembly table, however, are susceptible to wear and, at least to some extent, to problems caused by fouling. Furthermore, the truss parts still are laid manually which is both time-consuming, and includes plenty of possibilities for errors even if assisted, for example, by projecting the parts' position on the assembly table using a laser light.

Parts laid into position are joined together by nail plates to be pressed against the node joints of the struts. For preliminary pressing, for example, a beam press can be used pressing the plates into the struts deep enough for the structure to hold together upon handling. Generally, the nail plates are pressed to final depth in this case by a massive roll press. For pressing the nail plates into the struts, also a so-called C-clamp fastened movable to support structures above the assembly table can be used.

In order to facilitate manual turning of the truss upside down, solutions have also been developed. In patent specification EP1087071, for example, an assembly table is disclosed provided with a turning member for turning the truss upside down, allowing the nail plates to be mounted on the other side of the truss, too. By such a turning member, however, the complexity of the apparatus is increased, and utilises more movable parts susceptible to wear and damage.

In patent specification EP 0653977 B1 a device for manufacturing roof trusses is disclosed, in which the assembly table is formed of pressing heads movable in one plane, movable to positions required by the node joints of the truss structure, and parts of the truss can be positioned by using the pressing heads and auxiliary means fastened thereto. In this solution also, a setting for controlling the positioning of the truss parts first must be made slowing down the change of truss type to be manufactured. Additionally, even when using this device, the wooden parts must be brought manually into position.

As can be seen from above, even today the manufacture of trusses is rather time-consuming, requiring still fairly many manual steps of work which, in addition to causing costs, tends to increase errors and inaccuracies. The mechanisms moving the stops in the assembly table, needed for forming the setting, are susceptible to wear and problems caused by fouling. Turning a half-finished truss upside down adds to the difficulties of the method, and renders the joints of the truss susceptible to loosening and dislodging.

OBJECT OF THE INVENTION

The object of the invention is to provide alleviation for the drawbacks mentioned above.

The invention is especially intended to disclose a novel automatic method and apparatus for manufacturing a nail plate truss without a setting, by means of which method and apparatus trusses having different shape and size can be manufactured effectively and with high accuracy, and which apparatus, compared to prior art apparatuses, is simpler and requires less maintenance.

SUMMARY OF THE INVENTION

The method and apparatus in accordance with the invention for manufacturing a nail plate truss without setting are characterised by what is respectively presented in the independent claims 1 and 7.

A nail plate truss manufactured using the method and apparatus according to the invention includes first-side nail plates of the truss, second-side nail plates of the truss, and struts joined together by nail plates. A typical nail plate truss is a roof truss carrying the outer roof of a building but, however, nail plate trusses also are used as skeletons for light-structure buildings, as bridge mould and fence structures. A truss to be manufactured at once, naturally, can also be just a part of a larger truss.

According to the invention, the structure of the nail plate truss to be manufactured, i.e. parts of the truss and their positions relative to each other, are first stored in an electric control system. In the assembly stage, the nail plates and struts for the truss are brought into their positions required by the truss structure, on a horizontal assembly table, as controlled by an electric control system, using handling members separate from said table. By transporting both the trusses and the struts mechanically in this way using the handling members, manual steps of work are completely avoided. Depending on the part of the truss to be transported and the assembly stage, the part can be brought directly onto the assembly table or on top of other parts already present thereon. In this case, the assembly table is a concrete level, e.g. of metal, rigid enough for the truss to be assembled thereon. Separate from the assembly table means that the handling member is not connected directly to the level but is supported to structures outside thereof. Furthermore, it is a characterising feature of the invention that, when transporting truss parts to the assembly table, they are put in their positions directly based on positioning of said handling members transporting the parts. In other words, positioning is not performed according to the prior art indirectly by first positioning stops and limiters, or other corresponding members on the assembly table forming the setting, but final positioning of the part is directly depending on positioning of the handling member positioned precisely, and on the position of the truss part to be transported relative to the handling member.

In greater detail, as controlled by the electric control system, the inventive method can comprise steps for

    • by using the handling members, fetching the first-side nail plates of the truss from the respective pick-up positions, and above the assembly table, transporting them directly into their positions at the node joints of the truss on the assembly table, and fastening them to the assembly table with their nail sections showing upwardly,
    • picking up the struts for the truss from the respective pick-up positions by the handling members and, above the assembly table, bringing them directly to their positions above the first-side nail plates of the truss, present on the assembly table, and pressing them by the handling members against the nail plates, and
    • picking up the second-side nail plates of the truss from the respective pick-up positions by the handling members, and above the assembly table, transporting them directly into their positions at the node joints of the truss above the struts present on the table, having the nail sections showing downwardly, and pressing them by handling members against the struts, and
    • furthermore, as controlled by the electric control system, disengaging the fastening of the first-side nail plates of the nail plate truss to the assembly table, and removing the truss from the assembly table, for example, onto a conveyor outside the assembly table, to be transported for further treatment or storage.

Performing the steps described above as controlled by the electric control system means that said steps are performed automatically by means especially provided for each step. For transferring and positioning of parts, for example, handling members can be used operated by precisely positioned electric high-speed linear motors provided with slides for linear motors moving in a magnetic trail, to which the handling members have been fastened. By automation, the manufacture is accelerated, and positioning the parts becomes more precise while simultaneously reducing the possibility of errors compared to manual assembly. Said pick-up positions may be storages or intermediate positions for parts outside the assembly table or in the area of the table, to which parts needed at each time are brought one by one. In their respective pick-up positions, both the struts and the nail plates are preferably in precisely defined locations in order to be gripped at given locations, when picking up by automatic handling means. At this, the location of the parts is under control during the entire transfer. If the pick-up position is a storage containing several different parts, the parts are preferably provided with identifications, e.g. bar codes or the like allowing the handling members to identify, for example, the strut needed in each case.

Each one of the parts of the truss can be transported into their positions one by one. Handlings members to be moved, for example, by linear motors, however, can be controlled independently relative to each other, allowing several parts to be transported simultaneously, thus speeding up the assembly. Instead of bringing all the first-side nail plates onto the assembly table before the struts, the truss, naturally, can also be assembled from sections, whereupon just part of the nail plates and struts for the truss is mounted. Node joints denote points of the truss where, typically at different angles, the struts are joined together. Pressing the parts against each other means that the nail portions of the nail plates penetrate into the struts, preferably so deeply that the truss, having also the nail plates on the other side pressed into the struts, will hold together and maintain its form upon transportation. For ensuring the accuracy upon assembly, the strut preferably is hold by one handling member at each node joint of the strut. Then, even the node joints of a possibly crooked strut may be precisely forced in place.

In an embodiment of the invention, the node joints of a nail plate truss removed from the assembly table are tightened to have their final strength, by pressing the nail plates into the struts over the entire length of their nail portions. This pressing finally completing the truss can be performed, for example, using a roll press common in the roof truss industry.

In a preferred embodiment of the invention, in the area of the node joints, the assembly table is magnetised, preferably as controlled by an electrical control system, for fastening the first-side nail plates of the nail plate truss thereto. In doing so, the assembly table itself may be a very simple, merely a planar surface, for example a continuous or even a net-like steel structure. Thereby, the magnetising means is preferably disposed beneath the assembly table.

In a further embodiment of the invention, when contacting a strut with another strut, its vertical surface is first laterally contacted with the vertical surface of another strut and, following this, vertically pressed against the nail plate. In this way, by laterally contacting the strut with another strut, it will be ensured that the truss, upon pressing against the nail plate, will not be borne by another strut, and the struts are joined together as tightly as possible in order to form a strong joint. Hence, also possible positioning and form faults of a strut previously assembled are detected, as due to the fault, the strut cannot be brought into its position, while abutting on the strut previously assembled. Also in this solution, final positioning of the strut is determined directly, as controlled by the control system, based on positioning of the handling member.

Preferably, the strut is pressed against a first-side nail plate present on the assembly table by means of one handling member at each node joint, i.e. at each first-side nail plate to be connected with the respective strut. Concentrating the pressure specifically on the nail plate is important because, when pressing a longish bending strut at another location, the nail plate will necessarily not be pressed deep enough into the strut. It also is possible to realise pressing by a single rigid pressing organ extending across the entire length of the strut.

In order to render pressing of struts and nail plates against each other more effective, the strut and/or the nail plate on the other side of the truss can also be vibrated when pressing the strut against the first-side nail plate, and/or the second-side nail plate into the strut. Hereby, a smaller force can be applied when pressing, or alternatively, the nail plates will be pressed deeper into the struts by using the same force. Particularly in the case of light-structure trusses, the nail plates may be pressed in this way up to the base, that is, corresponding to the entire length of their nail portions, with no separate repressing strengthening the nodes being needed.

According to the invention, the apparatus for manufacturing the nail plate truss without setting includes an electric control system in which the structure of the truss, and the positions of its parts can be stored. The control system may include, for example, both a computer and software installed therein, and data transfer connections between the computer and the apparatuses controlled by it. The control system allows the nail plate trusses to be manufactured automatically, without manual working steps, thus contributing to the effectiveness of the manufacture, and decreasing the production costs. The accuracy also is improved as human errors, for example, in measuring the positions, are eliminated. Such a control system also can be integrated as a part of the remaining production control system of the factory, allowing the apparatus to be operated centrally as a part of the controlled production line.

The apparatus also includes a horizontal, fixed and continuous assembly table for assembling the nail plate truss as supported thereon. Fixed and continuous means that the assembly table is substantially continuous, and does not contain any partial levels movable relative to each other. The assembly table can merely be, for example, a continuous or net-like level of steel without any prior art stops movable along the surface plane. Furthermore, the apparatus preferably includes fasteners controlled by the electrical control system, for fastening the first-side nail plates to the assembly table. By means of the fasteners, the first-side nail plates and, thus the entire truss structure, can be maintained in given positions during the assembly. By maintaining the parts in position, the accuracy is ensured during assembly of parts of the truss, accomplished on the basis of data stored in the electric control system.

In addition, the apparatus comprises handling members separate from the assembly table and supported thereabove, controllable by the electric control system, including gripping means for gripping the nail plate and the strut, as well as pressure members for pressing the struts and the nail plates against each other. Preferably, there are at least as many handling members as one strut has maximally node joints. Furthermore, the apparatus comprises electrical transfer means controlled by the electrical control system, allowing the transfer means to be moved above the assembly table, and positioning the same. Thus, as controlled by the electrical control system, the movable handling members can be used for fetching the truss parts from their pick-up positions, and bringing them precisely into their positions on the assembly table required by the truss structure, or on nail plates or struts already present thereon. Using the same handling members, the nail plates and struts can be pressed against each other, and finally, the truss thus assembled can be removed further away from the assembly table.

In a preferred embodiment of the invention, the fasteners are magnetising means for magnetising the assembly table in the area of the node joints. By magnetising the assembly table, the nail plates of metal can be firmly maintained in position on the assembly table during the manufacture of the truss. The magnetising means may include electromagnets which, when appropriately electrically controlled, allow the magnetising to be quickly switched on and off. Also permanent magnets arranged, for example, to be swivelling may be used which, upon swivelling relative to the assembly table, allow the assembly table to be magnetised and demagnetised.

In one embodiment of the invention, the gripping means include opposed gripping members movable relative to each other, for gripping the nail plate or the strut by pressing it between the gripping members. The gripping members may be for example vertical surfaces, or grab-like members hinged to be swivelled against each other. The gripping members may be arranged suitable for bringing in an evasion position one by one. By bringing one of the gripping members in the evasion position, a strut may be contacted with another strut while, however, supporting it near to the contact point of the struts by another gripping member.

The gripping means can comprise negative pressure means for gripping the strut by means of negative pressure. This is advantageous, for example, when tightening the grip in the case described above, in which one of the gripping members has been brought into the evasion position. When fetching a strut from the store, from one of the strut stacks, a situation also may occur where there is no place for one or either gripping members to grip the rod. For lifting the strut from the stack, it may be gripped by means of negative pressure.

The gripping means may further comprise magnetic members for gripping the nail plates. The magnetic means may be useful, for example, when fetching a nail plate from its pick-up position between other nail plates, when there is no place for the gripping means to be used. Gripping nail plates of steel also can be accomplished merely by magnetic means without the use of other gripping means.

The pressing means preferably comprise a support surface, and a drive for pressing the support surface towards the assembly table so as to press the nail plate and the strut against each other. For the support surface, it is useful to have at least the size of the nail plates, for allowing the nail plates to be pressed against the struts uniformly over their entire area. The support surface may be, for example, a continuous or grid-like steel surface. The drive may be, for instance, a hydraulic cylinder or another corresponding device, allowing an adequate pressure, preferably at least 15 to 20 tons, to be applied against the strut or the second-side nail plate.

The handling means also may comprise vibrating means for vibrating the support surface, so as to increase the effectiveness while pressing the nail plate and the strut against each other.

In a preferred embodiment of the invention, the transfer means first include linear guides arranged above the assembly table, substantially parallel thereto, carrying the handling members for transferring the handling members along the first linear guides. Furthermore, the transfer means comprise second linear guides supported above the assembly table, for example, to the frame of the apparatus, carrying the first linear guides, and arranged perpendicularly thereto, likewise disposed substantially parallel to the assembly table for transferring the first linear guides therealong. Hence, by means of linear movements in two directions, the handling member can be brought to every given position above the assembly table. The linear guides extend preferably over the entire handling line and so far therebeyond that fetching parts from pick-up positions outside the assembly table, and transfer of the truss away from the assembly table is enabled. Preferably, the handling member also is arranged to be horizontally movable, transversely in relation to the first linear guide carrying it. This allows moving and assembling of the struts also parallel to the first linear guide, by holding the strut with the handling members of the first linear guides. For accomplishing the movements along the linear guides, the transfer means also comprise drive means, for example linear electric motors or other drive means capable of achieving sufficient speed and positioning precision.

For each handling member, the transfer means preferably include a lifting device for transferring the handling member perpendicularly in relation to the assembly table, i.e. vertically, for lifting truss parts from their pick-up positions, for transferring them into given positions above the assembly table, and for lowering them onto the assembly table or near it. For each handling member, the transferring means likewise comprise preferably an rotational device for rotating the handling member about its vertical axis allowing the parts to be positioned at the necessary angles.

Utilising the inventive method and apparatus for the manufacture of nail plate trusses, different advantages are achieved, as is described above, compared to previously used methods. Firstly, the assembly of nail plate trusses in which conventionally a lot of human work was involved, can be completely automated resulting in an acceleration of the manufacture. Additionally, time is spared remarkably by the essential feature of the invention that a separate change of setting between the different truss types is not needed, since positioning of the parts is directly based on position information stored in the electric control system, and on positioning of the handling members as controlled by the control system. By automation, the precision also will be improved and the possibility of errors minimised. The automation system can be incorporated as a part of the remaining control system so as to be operated by the production control system of the entire production plant. According to the invention, the nail plate truss is manufactured without turning upside down known from prior art, for fastening the second-side nail plates. This eliminates the risk for truss to be distorted during turning. Neither are complicated and failure-prone to turning means needed known from prior art apparatuses. Unlike the stops according to prior art, movable in the assembly table, the apparatus is not sensitive to problems caused by wooden material loosening from the trusses, and other impurities, as the assembly table may be very simple, for example, merely a level of steel.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described in detail with reference to the accompanying drawings, in which

FIG. 1 shows schematically a method according to the invention,

FIG. 2a, 2b and 2c show an embodiment of the invention, and

FIG. 3 shows a perspective view on the structure of an inventive apparatus,

DETAILED DESCRIPTION OF THE INVENTION

In the method according to FIG. 1, the truss structure, as well as the position information of parts thereof are stored in an electric control system allowing, in the control of which the truss parts are fetched from their pick-up positions by handling members movable above the assembly table, for example, by electric linear motors, transporting them into their positions on the assembly table or thereabove, required by the truss structure, and assembling them using the same handling members by pressing the struts and nail plates against each other by the handling members. The first-side nail plates are fastened to the assembly table by magnetising it in the area of the node joints. Following the assembly of the parts, the truss is removed from the assembly table, and tightened to final strength by pressing the nail plates into the struts over the entire length of their nail portions, for example, utilising a roll press traversing over the truss. In the method shown in FIG. 2a, 2b and 2c, mounting of strut 4a with its lateral face contacting another parallel strut 4b, is illustrated. Using a handling member 11, the strut 4a is first brought horizontally to a distance from the second strut 4b and, as indicated by the arrow in FIG. 2a, lowered to be partially flush therewith, after which it is laterally contacted with the other strut 4b. In FIG. 2, the strut 4a has thus been contacted with the other strut 4b. From the same figure, it also can be seen how one of the gripping members 13 of the handling member has been brought in evasion position. At the same time, the grip has preferably been tightened by negative pressure created by negative pressure means arranged in the handling member. In FIG. 2c, the last stage is shown with the strut 4a being pressed, for example, by means of a hydraulic drive 15 through a support surface 14 against a nail plate 3 on the assembly table. Hence, by first laterally contacting the struts it is ensured that a strut 4a having possibly a slightly inaccurate form will not be carried at any point by the other strut 4b. At the same time, the struts are settled tightly against each other. In the figures, also an auxiliary gripping device 21 is showed which can be, for example, a negative pressure arrangement for gripping truss parts by means of negative pressure, or a magnetic device for gripping the nail plates by means of magnetism.

The apparatus 1 in FIG. 3 includes a substantially horizontal assembly table 5 shown partly in sectional view for the assembly of nail plate trusses 2 thereon and supported thereon. The assembly table 5 consists of two layers the upper one being a continuous upper plane 6 of steel. Therebelow an approximately 40 to 50 mm thick lower steel level 7 is disposed having holes 8 with given spacing, in which electromagnets 9 are disposed. By switching the electromagnet 9 on, the upper steel level 6 is magnetised at the hole and in its vicinity. The electromagnets 9 are preferably arranged to be switched on separately. Hence, during the manufacture of each truss 2, it is sufficient to use electromagnets 9 disposed near the node joints only. Spaced from the assembly level 5, above the same, there are first linear guides 10 supporting the handling members 11 allowing the nail plate truss 2, the nail plates 3 and the struts 4 to be transported and assembled. The handling members 11 are arranged to be movable parallel to the assembly level 5 along first linear guides 10, and transversely thereto as well, for raising and lowering them vertically and turning them about their vertical axis. The latter property is needed for assembling the struts and nail plates on the assembly at angles required by the truss structure. Said transverse movement enables transferring and assembly of the struts parallel to the first linear guides by using handling members of two adjacent first linear guides transferred in the direction of the first linear guides so as to be aligned. The first linear guides 10 again have been arranged to be movable along second linear 12 guides parallel to the assembly table, supporting them, arranged perpendicularly thereto, which have been fastened to the frame of the apparatus 1 (not shown in the figure). By means of two linear movements perpendicular to each other, any horizontal positioning of the handling members may be accomplished. The linear guides 10, 12 extend beyond the assembly table 5 for picking up struts 4 and nail plates 3 by handling members 11 from their pick-up positions 19 outside the assembly table, only one of which is indicated in the figure and, for removing the nail plate truss 2 from the assembly table 5. The movement of the handling members along the first linear guides, and the movement of the first linear guides along the second linear guides is accomplished by electric linear motors, the moving portion 16 of one of them being shown in the figure. For the vertical and turning movement of the handling means, the handling member has a lifting and rotating mechanism 17, 18. The handling members 11 comprise gripping means 13 for gripping struts 4 and nail plates 3 by clamping them between the gripping means. The handling members 11 also comprise a support surface 14 for pressing the struts 4 and the nail plates 3 against each other.

As an essential part, the apparatus 1 also includes an electric control system 20 in which the structure of the truss 2 to be manufactured, i.e. the parts 3 and 4 thereof, and their positions can be stored. The data transfer connection between the control system and the other parts is not shown in the figure. By the control system, preferably the movement of the handling members 11 and the first linear guides 10, operation of the gripping means 13 and the support surface 14, as well as the electromagnets 9 for the assembly table 5, are controlled. The electric control system can be connected with the production control system of the entire plant allowing the apparatus 1 to be used as a part of the centrally controlled production line.

In FIG. 3, a step in manufacturing a simple imaginary nail plate truss 2 also is shown. The truss 2 consists of three struts 4 and nail plates 3 joining them together. In the stage showed in the figure, the struts 4 forming the edges of the truss 2 have already been connected with each other by a nail plate extending over their node joint, in the figure invisible under the struts. Two other nail plates 3 are on the assembly table 5 partially under the two edge struts allowing a third strut to be connected between the edge struts by these nail plates. At the nail plates 3, the third strut has been gripped by two handling members 11 for bringing the strut horizontally into position, in contact with the two other struts and, by means of the support surface of the handling member 11, pressing them against the nail plates 14.

The invention is not limited to the embodiments previously disclosed, but several modifications are possible within the scope of the inventive idea defined by the claims.