The present invention also relates to plant for the manufacture of lattice elements for lattice trusses.

It is known in the manufacture of lattice trusses from wooden elements to place a number of support stools on a work surface in those positions in the roof trusses at which the truss elements shall be adjoined and fastened together. The truss elements are prefabricated from wooden beams, by cutting the beams in a program-controlled cutting machine which imparts a correct length and correct end-shapes to the elements, in accordance with a pre- set program.

In this regard, it is known to place the prefabricated elements on the support stools and to adjoin the elements at pre-selected positions, which can be marked by projecting light images onto the element adjoining regions, for instance. These projected images provide accurate mutual positioning of the ends of the elements, and also accurate orientation of the prefabricated elements. It is also well known to mount on the stools guide fittings in which nailing plates can be first placed in correct positions and orientated relative to the element joins that are later established above the nailing plates. Naturally, the element joins can be positioned correctly with the aid of other means.

One problem encountered with such manufacturing techniques is that positioning of upper nailing plates above the joins between the lain-out truss elements is time-consuming, even though it is possible to mark correctly and to orientate correctly said upper nailing plates with the aid of image projectors, since the size and configuration of the images projected are normally dependent on the direction of projection and on the distance of said projection. Although program-controlled automated placement of the upper nailing plates is a possibility, it is not economically defensible in relation to the small numbers usually involved in the manufacture of roof trusses.

Accordingly, one object of the present invention is to provide a method and a plant for marking the positions and the orientation of the upper nailing plates on the adjoined but still unconnected elements of the roof truss in a simple and positive manner.

This object is achieved with a method according to the accompanying independent method Claim, and also with plant according to the accompanying independent apparatus Claim.

Basically, the invention relates to the manufacture of lattice trusses from straight wooden beams, wherein the beams are cut into lattice elements which are mutually adjoined in the configuration of a roof truss on a lay-up surface, wherein nailing plates for fastening together the adjoined elements are correctly positions and orientated relative to the upper side and the underside of the still unfastened roof truss and then driven into the adjoined lattice elements, wherein a significant feature of the invention lies in providing the truss elements with position markings that indicate where the nailing plates shall be mounted on the upper side of the roof truss, prior to joining the elements together. The position markings are adapted to provide clear information concerning the position and orientation of respective nailing plates on the upper side of the truss. Because the nailing plates shall bridge two or more elements, it is suitable to mark the contours of a nailing plate on the elements to be fastened together via said plates. The straight elements of a lattice truss are typically manufactured by passing wooden beams through a cross-cutting machine, which cross cuts the beams in accordance with a pre-set program, so that the elements will be given the correct lengths and the correct end-configurations for adjoining said elements. In one preferred embodiment of the invention, the markings for the overlying nailing plates can be drawn on the elements in conjunction with passing the wooden beams through the cross-cutting machine. In this case, the nailing plate markings can be drawn as the beams pass through the machine, wherewith the drawing devices can utilise the reference system of the machine to draw respective markings in correct positions on the elements.

Alternatively, an already manufactured element may, of course, be passed along a transport path that includes means for detecting a correctly cut end of the element as a reference for drawing a nailing plate marking on the otehrwise finished element.

According to one preferred embodiment of the invention, the cross-cutting machine can be equipped with simple means for writing the nailing plate markings on the elements in

conjunction with giving said elements an appropriate length and end-configuration in accordance with a pre-set program.

Embodiments of the invention will be apparent from the accompanying dependent Claims.

The invention will now be described by way of example and with reference to the accompanying drawing.

Fig. 1 is a horizontal view of a schematically illustrated arrangement for joining a wooden lattice beam.

Fig. 2 is a horizontal view illustrating schematically all arrangement for producing roof truss elements that can be joined together to form a roof truss or some like structure.

Fig. 1 shows a number of stools 11 which are set out on a generally horizontal support surface at those positions in which roof truss elements 10,20,21,31-34 shall be adjoined and mutually fastened to form a roof truss.

It will be seen from the illustrated example that a number of different, straight truss elements 10, 20,21,31-34 are prefabricated in chosen lengths and with chosen end- configurations, so that they can be adjoined effectively in one plane in a truss configuration. The elements are fastened together by means of nailing plates 2 that bridge the joins between the elements. These nailing plates shall be chosen in accordance with the strength requirements of respective joins and may have mutually different sizes. The nailing plates shall also be applied in correct, predetermined positions and orientations both on the underside and on the upper side of the truss lain out in a horizontal plane. Jigs that facilitate manual placement of the lower nailing plates in correct positions can be mounted on the stools 11 prior to laying out lattice elements on the stools 11 and adjoining said elements. The joins of said elements can be established in predetermined positions and in predetermined orientations, for instance with the aid of guides carried by the stools 11 or with the aid of light images projected from overhead projectors, wherewith the projected images indicate the correct positioning and orientation of the ends of the elements in respect of butt joints.

Such projector systems may, of course, also be used to project the correct positions and orientations of the nailing plates to be laid but on the joins on the upper side of the truss, although such laying-out and projection operations are relatively time-consuming.

The elements 10,20,21,31-34 are typically pre-maliufactured in a cross-cutting machine which, in principle, includes a travel path which provides an abutment and a guide 60 for one long edge of a wooden beam 18 to be cut into lattice elements. The machine 46 includes a cross-cutting saw 50, which can be given a chosen orientation in relation to the longitudinal axis of the beam 18. The machine also includes measuring equipment 47,48 for cutting the beam into pre-programmed lengths, wherein the cuts are also made at angles which are pre-programmed to produce correctly configured elements.

Thus, the cross-cutting machine 46 works on the basis of a pre-set program and therewith utilises measuring references that are chosen in a conventional manner.

According to one embodiment of the invention, the cross-cutting machine 46 can be equipped with a drawing device 49, which is controlled by a pre-programmed computer 47 such as to draw on respective elements to be produced in said machine at least parts of the contour 1 of an upper nailing plate 2 in a predetermined position for said plate.

When the elements are adjoined correctly on respective stools 11, said elements will thus carry markings 1 drawn in the join region of the upper nailing plates 2, therewith facilitating correct positioning of the nailing plates. When the upper nailing plates have been laid out in their correct positions, the truss can be finally manufactured by pressing the upper and lower nailing plates into the elements at their adjoining positions.

The drawing device can utilise the same reference system and sensor system 48 originally built into the cross-cutting machine and connected to the computer 47.

It will, however, be evident that equipment for drawing the positions of the nailing plates on said elements may be disposed along a wooden beam travel path 60 at a distance from the cross-cutting blade 50, for instance downstream thereof, although it is suitable for practical purposes to allow the drawing devices to draw their markings on a beam 18 or on an element 10,20,21,31-34 as the beam/the element is sensed in the machien by sensors

48 and, its position determined in the reference system of said machine, so as to enable the drawing equipment to be connected directly to the control computer of said machine.

The cross-cutting machine may also include a travelling path that is provided with an edge guide 60 and drive rollers 70 for wooden beams 80 that shall be displaced relative to the saw blade 50 along the guide 60. The saw blade 50 is suitably arranged to end-cut a beam for producing a butt joint in the truss.

Alternatively, the cross-cutting machine may, of course, be adapted to sense the longitudinal direction of the beam either directly or indirectly and to cross-cut the beams so that they obtain a predetermined shape and so that the element is given a predetermined length.

Because the markings on the element in the case of a correct join together indicate the contours of a pre-selected nailing plate, an operator can readily decide whether or not he is placing over a join a nailing plate of the correct size. Moreover, the operator can readily determine whether or not the joins are correct, since a correct join will mean that the markings form the contours of a nailing plate of a well-known shape, which is typically rectangular.

Both of these latter checks may, of course, be carried out with the aid of optical sensing equipment.

The drawing devices are suitably adapted to draw the markings so that they will form a contour whose size corresponds to the contour of the nailing plate to be applied. The size of the nailing plates will typically correspond to the strength requirements of respective joins, and/or the configuration of the joins.