The present invention relates to a micro trenching laying device and a method for micro trenching and laying of a duct or a duct tube in a micro trench.

Micro trenching is a known way of laying cables or ducts into the ground, in particular below a paved surface, such as along a street. Using micro trenching, rather than removing a wide strip of the paved surface; digging a wide trench, laying the cable or duct at the bottom of the trench; refilling the trench; and repaving the resulting surface, only a very narrow trench is instead sawn, using a saw blade, and the cable or duct is placed into the trench while it is being sawn. When the trench is complete, only a small volume of refilling material is required, and the top part can be sealed using a suitable sealant, such as a flexible mastic, to restore the surface to its original quality.

It is known, in the art of such micro trenching, to use a combined stabilization device and guide means being arranged behind the saw blade, and during use guiding the cable or duct down into the trench while also preventing the trench walls from collapsing before the cable or duct has come to rest at the bottom of the trench.

Such micro trenching has turned out to be very cost-efficient and fast, as compared to making a wider trench, for laying of cables and ducts, and in particular for laying of fibre cable ducts in residential areas. In the latter case, a main trench is sawn along a street, and shorter access trenches are branched off to each of the houses to connect to the fibre network.

Such a micro trenching device is previously known from Swedish patent with publication number SE 537 130.

However, it has turned out that it is not as easy to achieve high working efficiency when laying such access trenches, as compared to the main trench. The reason for this is that access trenches are sawn perpendicularly to the main direction of the street. Since the saw blade and the stabilization device are quite bulky, it is typically not possible to lay the cable or duct along the entire necessary access trench length, from the intersection with the main trench and up to each house to be connected. Instead, access trenches are often sawn using a separate, smaller saw, without a stabilizing device of the above described type. Thereafter, the cable or duct is placed in the sawn access trench manually afterwards. This proce- dure takes considerably more time per trench meter than for the main trench.

Furthermore, once arrived at the property to connect, it is often desired to draw the cable or duct underground up to a delivery point at the house; on a lawn; or similar. Then, the cable or duct needs to be drawn through a through hole beneath any pavement, property wall, fencing or the like, in order not to have to remove and then restore such structures. This also amounts to much manual labour.

The present invention solves the above described problems. Hence, the invention relates to a stabilizing device for a micro trenching laying device, which laying device comprises a circular saw blade arranged to saw a trench into the ground, which stabilizing device is arranged to prevent the trench behind the saw blade from collapsing as the saw blade of the laying device moves forward, which stabilizing device is characterised in that the stabilizing device is arranged to be pivotably connected to the laying device so that a centre of rotation of the stabilizing device lies maximally 5 cm from a centre of rotation of the saw blade; the stabilizing device is arranged with an engagement means arranged to non-slidably engage, at an engagement point, with a cable, duct or tube; and the said pivotable connection is arranged to allow the stabilizing device to pivot from a first position in which the engagement point is arranged behind the centre of rotation of the saw blade and to a second position in which the engagement point is arranged in front of the centre of rotation of the saw blade, between which first and second positions the engagement point travels below the saw blade.

The method also relates to a micro trenching method, in which method a circular saw blade of a micro trenching laying device is caused to saw a trench into the ground while a driving means drives the laying device in a forward direction, wherein a stabilizing device of the said laying device prevents the trench behind the saw blade from collapsing as the saw blade moves forward, which method is characterised in that the method comprises the steps a) attaching a duct or a duct tube to the stabilizing device so as to achieve a non- slidable engagement between said cable, duct or tube and said stabilizing device at an en- gagement point; b) driving the laying device in the forward direction, while the stabilizing device drags the cable, duct or tube along the sawn trench; c) bringing the laying device to a standstill at a stop point, and pivoting the stabilizing device so that the engagement point travels below the saw blade and to a position in front of the centre of rotation of the saw blade; and d) disengaging the cable, duct or tube from the stabilizing device.

In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the enclosed drawings, wherein:

Figure 1 is a simplified side view of a micro trenching laying device according to the present invention, in a first position when performing a method according to the invention;

Figure 2 is a simplified side view of the device shown in figure 1, in a second position in said method;

Figure 3 is a simplified side view of the device shown in figure 1, in a third position in said method;

Figure 4 is a simplified side view of the device shown in figure 1, in a fourth position in said method;

Figure 5 is a top view of a street along which the device shown in figure 1 is performing micro trenching; and

Figure 6 is a flow chart illustrating said method according to the present invention.

All figures share the same set of reference numerals.

Figure 1 shows a micro trenching laying device or machine 100, arranged to saw a micro trench 20 in the ground 10 using a rotary circular saw blade 102. Preferably, the ground 10 comprises a top surface, which is preferably paved, such as an asphalt or concrete surface, as well as a lower layer, which is preferably a granular material such as gravel. The top surface is preferably between 1-10 cm thick, and the total depth of the trench 20 is preferably 20-50 cm. Furthermore, the trench 20 is preferably at least 1 cm wide, preferably at least 2 cm wide, preferably at least 3 cm wide. Also, the trench 20 is preferably at the most 6 cm wide, preferably at the most 5 cm wide, most preferably at the most 4 cm wide. Typically, the ground 10 may be a paved residential street.

The saw blade 102 is preferably a diamond saw blade, in other words comprises diamond elements on the wear surface arranged for the cutting action. The saw blade 102 is prefer- ably operated in an up-cut fashion, rotating counter-clockwise as viewed in figures 1-4. The machine 100 moves in a forward direction D during cutting, by the force of at least one driven wheel 101. Hence, the machine 100 comprises a driving means arranged to drive the machine 100 in the forward direction D. It is preferred that the direction D, in the main plane of the street of which the ground 10 is a part, at least has a component which is perpendicular to a main direction of said street and/or a main trench 22 (see figure 5) of the above described type. In other words, the direction D is not parallel to the said main street direction. Preferably, the direction D has an angle of at least 45° to the main street direction, and is most preferably substantially perpendicular to the main street direction. The reference numeral 11 denotes a side limit of the street, which may be marked by a pedestrian curb or pavement; a refuge; the end of an asphalt surface covering; a property limit; or the like. Preferably, the side limit 11 marks the sideways limit for micro trench sawing using the machine 100. Reference numeral 200 denotes a cable, such as a cable comprising or being an optical fibre; a duct for such a cable or any other suitable cable; or a tube for such a duct, or for such a cable or any other suitable cable. Several cables, ducts and/or tubes may also be used, which are then laid beside and/or on top of each other in the trench 20, simultaneously. In the following, the term "duct" will be used to denote all these possibilities. It is understood that a hollow duct or tube can be laid in a first step, after which optical fibre or any other cable can be inserted, such as by blowing, into the laid duct or tube. Combinations of cables, ducts and/or tubes are also possible.

Preferably, the duct 200 is laid in the sawn trench 20, preferably along substantially the entire length of the trench 20, and is then, in a subsequent step, drawn below and past the limit 11 and further to a property to be connected. This may for instance take place using a separately arranged tunnel 21, as is shown in figure 5. The tunnel 21 preferably extends further, generally in the forward direction D, up to a delivery point which is preferably located on a property to connect. Using a stabilizing device 110 according to the invention and as described hereinbelow causes such further laying of the duct 200 to be more efficient, since the duct 200 will be present at or near the tunnel 21 once finished laying in the trench 20.

Hence, according to the present invention the machine 100 comprises a stabilizing device 110 arranged to prevent the trench 20 behind the saw blade 102 from collapsing as the saw blade 102 moves forward D. The stabilizing device 110 is in some respects similar to a conventional stabilizing device 110 (such as a "plough" device) used behind saw blades in conventional micro trenching machines, notably in that it stabilizes the trench 20 so that the trench 20 walls do not collapse before the duct 200 has been received at or near the bottom of the trench 20. However, the stabilizing device 110 differs from such a conventional stabilizing device in at least one respect, namely that it does not engage in a slidable manner with the duct 200. In a conventional stabilizing device, the duct is guided down into the trench 20 while sawing, so that the duct 200 is fed to the stabilizing device and subsequently fed down into the trench 20 at the current location of the stabilizing device. Hence, the duct 200 lies still in the trench 20 in the conventional case but slides past the conventional stabilizing device as the machine 100 moves forward. Furthermore, the guide of such a conventional stabilizing device achieves a non-fatal bending of the duct 200, with a certain safe minimum bending radius as the duct slides down into the trench 20. In contrast thereto, the stabilizing device 110 according to the present invention is arranged with an engagement means, arranged to non-slidably engage, at an engagement point 112, with the duct 200. In other words, the duct cannot be slid along the said engagement point 112. As the machine 100 moves forward D, the stabilizing device 110 and hence the engagement point 112 as a result also move forward D, and the duct 200 is hence dragged along the trench 20 as the machine 100 moves forward D.

Furthermore, the stabilizing device 110 is pivotably connected to the machine 100 so that a centre of rotation 113 of the stabilizing device 110 lies maximally 5 cm from a centre of rotation of the saw blade 102. In other words, the stabilizing device 110 can pivot about said centre of rotation, whereby the stabilizing device 110 moves about the periphery of the saw blade 102. This is illustrated in figures 1-4.

In particular, the said pivotable connection between the stabilizing device 110 and the machine 100 is arranged so as to allow the stabilizing device 110 to pivot from a first position (illustrated in figures 2 and 3), in which the engagement point 112 is arranged behind the centre of rotation of the saw blade 102, and to a second position (illustrated in figure 4) in which the engagement point 112 is arranged in front of the centre of rotation of the saw blade 102, as seen in the forward direction D and as measured in a horizontal direction. When moving from said first to said second position and back, the engagement point 112 travels below the saw blade 102 in the trench 20. Preferably, said first and second positions are separated by between 30° and 180°, preferably between 40° and 120°, further preferably by at least 90°, in the rotary direction of said pivotable engagement. It is understood that the said first position is the one which should in general be used during sawing and movement forward D of the machine 100, and that the stabilizing function of the stabilizing device 110 is hence active when in said first position. Specifically, it is then arranged behind the saw blade 102 and into the trench 20, as illustrated in figures 2 and 3, preferably extending at least halfway down to the bottom of the sawn trench 20.

It is preferred that the stabilizing device 110 is lockable in the said first position, and, using a control means, unlockable so as to be pivoted to the said second position. The pivoting action of the stabilizing device 110 is preferably hydraulically driven, preferably using power provided by a main motor of the machine 100. Preferably, the stabilizing device 110 is of generally elongated shape, and bent, with a width of at the most 10 cm along at least half of its length, preferably along substantially or completely its entire length. In particular, it is preferred that the elongated shape of the stabilizing device 110 is such that the trench 20 stabilizing function of the stabilizing device 110 is active not only in said first position, but also in said second position.

Preferably, the engagement point 112 is arranged at an end of the stabilizing device 110, preferably at a distal end facing down into the trench in said first position.

Further preferably, the stabilizing device 110 has a shape which is complementary to the periphery of the saw blade 102, at least along a section of the length of the stabilizing device 110. Preferably, it is the generally bent shape of the stabilizing device 110 which achieves the said complementary shape.

The pivotable engagement between the stabilizing device 110 and the machine 100 can be arranged in different ways. A preferred such way is illustrated in the figures, in which the stabilizing device 110 is pivotably fastened, such as journaled, at 113, to the same axis as the saw blade 102. This is illustrated in the figures.

However, in an alternative embodiment, which is not shown in the figures, the stabilizing device 110 is pivotably fastened, such as journaled, separately from a saw blade axis. For instance, the stabilizing device 110 may be fastened to a separate axis arranged adjacent to the saw blade 102 axis; or a rod may connect the stabilizing device 110 to a guide track on the machine 100.

According to a preferred embodiment illustrated in figure 1, the stabilizing device 110 can also be pivoted to a third position, in which said engagement point 112 is located above ground 10 behind the saw blade 102. This simplifies the fastening of the duct 200 at the engagement point 112. Moreover, the said second position of the stabilizing device 110 may provide the engagement point 112 above ground 10, but in front of the saw blade 102, as illustrated in figure 4. In this case, the stabilization device 110 is hence pivotable across a total angular interval of more than 180°, which total interval is longer than between said first and second positions. It is, however, preferred that the stabilizing device 110 is not pivotable a full 360°.

According to a preferred embodiment, the machine 100 furthermore comprises a distribution device 120 for granular material, such as sand. The distribution device 120 is then arranged to provide such granular material into the trench 20 behind the saw blade 102 as the machine 100 moves forward D. In the exemplifying embodiment shown in figures 1-4, the distribution device 120 is in the form of a container with a lower opening. During operation, the distribution device 120 is loaded with sand or other granular material and distributes the loaded material via the lower opening as the machine 100 progresses along the direction D, preferably so that the granular material covers and hence protects the duct 200 in the trench 20.

Preferably, the distribution device 120 is pivotably connected to the machine 100 in a manner which may be of one of the exemplifying types as described above in relation to the pivotable connection of the stabilizing device 110, such as using a journaled engagement. Preferably the pivotable connection of the distribution device 120 is arranged so that the distribution device 120 can pivot independently of the stabilizing device 110, about an axis 123 which may be the same axis as the stabilization device 110 pivot axis 113. The pivot- ability, and in particular the said independent pivotability, provides good flexibility when operating close to a main trench 22 and/or a street limit 11.

Further preferably, the distribution device 120 is arranged behind the stabilizing device 110 as seen in the forward direction D, at least so that distributed granular material in the trench 20 ends up on top of a laid duct 200.

In the figures, a rod 122 for attaching the distribution device 122 to the pivot axis 123 is also illustrated. It is preferred that the height of the saw blade 102 is vertically adjustable in relation to the ground 10.

Figure 6 illustrates a micro trenching method according to the present invention, for sawing a micro trench and laying a cable, duct and/or tube of the above described type in the sawn trench. The method is also illustrated, step by step, in figures 1-4.

More particularly, in such a method, the circular saw blade 102 of the micro trenching laying device or machine 100 is caused to saw the trench 20 into the ground 10 while the said driving means drives the machine 100 in the forward direction D. Furthermore, in a method according to the present invention, the stabilizing device 110 is used to prevent the trench 20 behind the saw blade 102 from collapsing as the saw blade 102 moves forward D.

In a first step of the method, the duct 200 is attached to the stabilizing device 110 so as to achieve a non-slidable engagement of the above described type, between the duct 200 and the stabilizing device 110 at the engagement point 112. This step is preferably performed in the position of the stabilizing device 110 illustrated in figure 1, with the engagement point 112 located above ground 10 and behind the saw blade 102. Furthermore, this method step is illustrated in figure 1 in the sense that it takes place at the beginning of the sawing of the access trench 20, preferably beginning at a main trench 22 (see figure 5) and sawing towards the street limit 11. More precisely, in figure 1 a stretch of access trench 20 has been sawn which is only long enough for the stabilizing device 110 to just fit into the access trench 20 behind the saw blade 102.

Thereafter, the stabilizing device 110 is preferably lowered, that is pivoted in the clockwise direction as shown in figure 1, to the above described first position. Then, the machine 100 is set in motion and the saw blade 102 is activated to continue sawing the access trench 20 in the forward direction D.

Hence, the duct 200 is preferably attached to the stabilizing device 110 at the engagement point 112 which is then arranged above ground 10, after which the stabilizing device 110 is pivoted so that the engagement point 112 is dislocated to a position below ground 10, behind the centre of rotation of the saw blade 102, for continued operation.

In a next step of said method, the machine 100 is hence driven in the forward direction D, while the stabilizing device 110 drags the duct 200 in and along the sawn access trench 20.

During the forward D motion of the machine 100, it is preferred that the engagement point 112 is arranged at the most 10 cm, more preferably at the most 6 cm, from the bottom of the sawn trench 20.

In order to protect the duct 200 during laying progress, it is furthermore preferred that the above described distribution device 120 is used to continuously distribute said granular material from above into the trench behind the stabilization device 110 into the trench 20 so as to cover the duct 200.

Moreover, in order to keep the duct 200 at the bottom of the trench 20, it is preferred that a guide means 130 is used to guide the duct 200 into the trench 20 at a fixed point behind the stabilizing device 110, such as at or near the beginning of the access trench 20. In figures 1-4, the guide means 130 comprises a wheel 131 guiding the duct 200 around a point ar- ranged at or near the bottom of the trench 20, while preserving a minimum curvature radius not risking to cause breaking damages to the duct 200, and while the duct 200 is being dragged, by the pulling action from the engagement point 112, past the wheel 131. Therefore, the wheel 131 preferably has a duct-contacting radius of at least 5 cm. Preferably, the guide means 130 may comprise means for preserving an order of a set of ducts 200 simultaneously placed in the trench 20. This is advantageous, for instance, when providing optical fibre to several properties along a street, since the order of the ducts from top to bottom in the trench 20 then reflects the order of connection along the street. It is, in this case, preferred that the trench 20 is narrow enough so as to allow only maximally 3, preferably only 2, ducts 200 beside each other in the trench 20. This simultaneous sawing, laying and covering action will then be performed continuously until the position of the machine 100 shown in figure 3 has been reached, in which the saw blade 102 has reached the limit 11 but a small distance which is necessary for handling of the duct after the engagement point has been moved to the front side of the saw blade 102 as described above.

At this point, the method comprises a step in which the machine 100 is brought to a standstill at the stop point shown in figure 3. In connection thereto, such as immediately after the stopping of the machine 100, the stabilizing device 110 is pivoted about the above described centre of rotation lying maximally 5 cm from a centre of rotation of the saw blade 102, so that the engagement point 112 travels below the saw blade 102 and to the position in front of the centre of rotation of the saw blade 102 illustrated in figure 4. Before the stabilizing device 110 is pivoted, the saw blade 102 is preferably raised as described above.

Then, after the stabilizing device 110 has reached the position illustrated in figure 4, the duct 200 is disengaged from the engagement point 112 and as a result from the stabilizing device 110.

At this point, the method may end, and an additional method may be commenced for handling the duct 200, and for providing it to the property. For instance, the duct 200 may be further dragged into and along the tunnel 21 and up to the property in question. Alternatively, the duct 200 may be buried in the ground in a different manner, as may be convenient, so as to reach the property.

Finally, the guide means 130 may be removed, and the trench 20 may be filled with granular material and then sealed with a suitable surface sealant. In case a cable duct or tube is used as the duct 200, a cable, such as an optical fibre, can then be blown, or otherwise inserted, into the duct 200 so as to finalize the installation. Above, preferred embodiments have been described. However, it is apparent to the skilled person that many modifications can be made to the disclosed embodiments without departing from the basic idea of the invention.

For instance, the guide means 130 may constitute an integrated part of the machine.

There may be many different types of peripheral equipment on the machine 100, such as a set of cable reels; a driver's seat or compartment; hydraulic and combustion engine power equipment; and so on.

The saw blade 102 may be of any suitable type, with or without cutting diamonds depending on the prerequisites. There may also be several saw blades, such as parallel saw blades for sawing a wider trench 20.

The stabilizing device 110 may have different constitutions than the one illustrated in the figures, as long as the above described principles are employed.

Furthermore, everything which has been said in relation to the machine 100 above is equally applicable to the described method, and vice versa.

Hence, the invention is not limited to the described embodiments, but can be varied within the scope of the enclosed claims.