Technical Field

The present invention relates to a machine for sawing micro trenches and placing ducts/cables in micro trenches. More specifically, the invention relates to a machine according to claim 1.

Background of the Invention

Micro Trenching is expected to become the dominating method for building Fiber- To-The- Home (FTTH) in areas with detached or semi-detached houses. In Sweden around 400 000 houses are expected to become connected to a fiber network during the next 5 - 10 years. The world market is enormous and may be estimated to around 100 - 500 times the Swedish market. This means that somewhere between 40 million to 200 million houses may become connected over the next 20 years. When placing ducts and/or cables in micro trenches a (road) sawing machine is used for sawing trenches in which the ducts/cables are placed.

Summary of the Invention

An object of the present invention is to provide a machine for sawing micro trenches and placing ducts/communication cables, which fully or in part solves the problems and drawbacks of prior art.

The above mentioned object is achieved with a machine arranged for sawing micro trenches and placing ducts/cables in micro trenches, said machine comprising:

- a saw blade arranged for sawing a micro trench in an area; said area comprising a first layer LI and a second layer L2, said first layer LI being a hard surface layer, such as asphalt or concrete and said second layer L2 being a bearing layer for said first layer LI and situated below said first layer LI, wherein said machine is arranged for sawing said micro trench through said first layer LI and into said second layer L2;

-a stabilizing device arranged for stabilizing the walls of said micro trench when placing ducts/cables into said micro trench, said stabilizing device having a front part and a back part, wherein said front part, during laying of said ducts/cables in said micro trench, being positioned immediately behind said saw blade and having a shape that is complementary to or near complementary to the shape of said saw blade, wherein said stabilizing device further comprising guiding means for guiding at least one duct/cable when placed into said micro trench;

said machine characterized by that said machine being arranged with two sawing devices placed behind and in parallel with said saw blade, one said sawing device on each side of said micro trench; wherein said sawing devices are sawing through said first layer LI in parallel with and on a certain distance from and on each side of said micro trench.

Embodiments of the machine according to the invention are defined in the appended dependent claims and disclosed in the following detailed description.

Other advantages and applications of the present invention will be apparent from the following detailed description of the invention.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain the present invention, in which:

• Figure 1 shows a flow chart of MTT;

• Figure 2 shows a flow chart of an embodiment of MTT;

• Figure 3a and 3b schematically shows a cross section of an area with a micro trench 1;

• Figure 4 schematically shows the cross section in figure 3, wherein the micro trench 1 is filled with filling material 6 such as sand and sealed with two sealing layers;

• Figure 5 shows a typical layout of a FTTH network;

• Figure 6 shows how to saw branches to individual homes from a main micro trench 7;

• Figure 7 shows branching to individual homes if guided boring is used instead of sawing;

• Figure 8 shows a sawing machine 8 with its saw blade/disc cutter 14 and a stabilizing device 13 for placing ducts/cables 2, 3 immediately behind the saw blade 14;

• Figure 9 shows a sawing machine 8 where the stabilizing device 13 is adapted for placing a plurality of ducts/cables 2, 3 at the same time while maintaining the order of the ducts/cables 2, 3 in the micro trench 1; and

• Figure 10 shows in detail where 15 to cut the top duct 2 so that it will be long enough to reach its final destination; Figure 11 shows important areas for controlling the movement of the stabilizing device 13. The areas are defined in a coordinate system with origin in the center of the saw blade 14 and are valid for all placements of the saw blade 14 and stabilizing device 13, whether on the left or right side of the sawing machine 8 or in front of or behind the sawing machine 8. Figure 11 also defines the coordinate system with origin in the center of the saw blade 14, used throughout this document.

Figure 12, 13 and 14 shows examples of movements of the stabilizing device 13 according to the invention, where figure 12 shows an example of a linear movement, figure 13 shows an example of a pendulum movement and figure 14 shows an example of a continuous movement containing the elements: rotation and movement of the center of rotation in x- and y-direction.

Figure 15 shows in detail the design of the attachment points for the link arms on the stabilizing device 13 so that the ducts 2 and cables 3 inserted in the guiding means 17 are not damaged when the stabilizing device 13 is rotated.

Figure 16 shows a micro trench 1 sawed by a sawing and laying machine 8 arranged with sawing devices sawing through the surface layer LI on both sides of the micro trench 1. The figure shows the result after the removal of the surface layer LI between the two saw traces made by the sawing devices. Detailed Description of the Invention

To solve the aforementioned and other problems, the present invention relates to a sawing machine 8 comprising a saw blade 14 arranged for sawing micro trenches 1 in an area. The machine 8 further comprises a stabilizing device 13 arranged for stabilizing the walls of the micro trench 1 when placing ducts/cables 2, 3 into the same. Moreover, the stabilizing device 13 is positioned immediately behind the saw blade 14 in the micro trench 1 and comprises guiding means 17 for guiding at least one duct/cable 2, 3 when placed into the micro trench 1.

The saw blade 14 and the corresponding stabilizing device 13 may be integrated with the sawing machine 8 and thereby forming a completely new machine type or designed as an attachment unit that can be attached to existing machines. The saw blade 14 and stabilizing device 13 may be placed on the right side of the machine 8 or on the left side. Other possible locations are in front of the machine 8 or behind. The following description relates to all possible locations of the saw blade 14 and stabilizing device 13 as the description only talks about the relative position of the stabilizing device 13 in relation to the saw blade 14.

The saw blade 14 and the stabilizing device 13 are height adjustable between a highest position ("transport position") and a lowest position ("operating position").

The movement of the saw blade 14 between the two extreme positions may be made using a vertical movement or a rotation movement. A rotation movement may be achieved by the saw blade 14 and its engine being attached using a hinge in one end and a lifting device in the other end. Thereby the saw blade 14 can be elevated and lowered with a rotation movement with the aid of the lifting device.

The movement of the stabilizing device 13 is more complicated. During the transition between the two extreme positions the stabilizing device 13 may not touch the saw blade 14 or the bottom of the micro trench 1 or the saw blade cover. In addition, as the elevation and lowering of the stabilizing device 13 may be performed while cables 3 and/or ducts 2 are inserted in the guiding means 17 in the stabilizing device 13, the design must provide enough clearance and ensure that minimum bending radius for ducts 2 and cables 3 are possible to keep within specified limits.

In its highest position the stabilizing device 13 is completely lifted above ground level 10 and with some ground clearance and in addition completely retracted and with some clearance behind (with respect to the sawing direction 9) the saw blade cover. In its lowest position the stabilizing device 13 is max 50 mm above bottom of the micro trench 1 and positioned immediately behind the saw blade 14 with a clearance of max 20 mm. This means that the movement of the stabilizing device 13 between the two extreme positions means a movement in x-direction of more than 0.8*r, where r is the saw blade 14 radius and more than 0.8*r in y- direction. When sawing, the saw blade 14 wears and thereby its diameter will decrease. This means that the distance between the saw blade 14 and the stabilizing device 13 will increase with time. At some point in time the distance may be large enough so that stones in the bearing layer may cause the stabilizing device 13 to get stuck in the micro trench 1. Therefore the link arms that perform the movement of the stabilizing device 13 as well as their anchor points in the sawing machine 8 must be very strong. This is important because if the stabilizing device 13 is stuck in the micro trench 1 for some reason, substantial forces may be applied to the stabilizing device 13 and to its lifting system and anchor points in the sawing machine 8. To compensate for the wear of the saw blade 14 it is necessary to have the position of the stabilizing device 13 adjustable with reference to the current saw blade 14 radius. The adjustment can be implemented using turnbuckles or similar devices or by separate engine devices.

The link arms for elevation and lowering of the stabilizing device 13 are powered by a dedicated engine (e.g. electrical or hydraulic). Further, a machine 8 with the saw blade 14 arranged on the side of the machine 8, may have on its left and right sides, in the sawing direction 9, quick mount attachments means and driving means for both the stabilizing device 13 and the saw blade 14, respectively. Thereby, any of the left or right sides of the sawing machine 8 can be used for sawing and placing ducts/cables 2, 3 which may be necessary due to hindering infrastructure, traffic situation in the areas, etc.

According to embodiments of the invention, the transition of the stabilizing device 13 between the two extreme positions can be made using a linear or sequential linear movement, a pendulum movement or a continuous or sequential movement containing the sub-elements: rotation and movement of the center of rotation in x- and/or y-direction. Finally the movement may be composed by a combination of two or three of the above said movements.

The movement of the stabilizing device 13 may be controlled mechanically by link arms with fixed anchor points and performed using a single electrical or hydraulic engine device or by a number of electrical or hydraulic engine devices under software control from a computer.

Said linear movement may be along a straight line with around 15 - 40° angle to the ground plane 10. Said sequential linear movement may be a near horizontal movement with 0 - 25° angle to the ground plane 10, when the stabilizing device 13 is close to its lowest position and a steeper slope or even a completely vertical movement when the stabilizing device 13 is away from the saw blade 14. Figure 12 shows an example of a movement along a straight line. Said pendulum movement has the advantage that it is simple to achieve and allows for a strong construction. The area A + B in figure 11 indicates possible locations for the center of rotation for a stiff pendulum movement. Area B is less attractive because it is an area needed for the saw blade 14 cover and for lifting the saw blade 14 to its transport position. The most attractive area is area A. Area A is located above or in front of the saw blade 14 and its cover when the saw blade 14 has been lifted to its transport position. Figure 13 shows an example of a stiff pendulum movement with center of rotation in area A.

A continuous movement of the stabilizing device 13 containing the sub elements: rotation and movement of the center of rotation in x- and/or y-direction may be achieved using two link arms. The most attractive position for the location of the anchor points of those link arms is area C (in figure 11) behind the saw blade 14 cover with respect to the sawing direction 9. The actual movement of the stabilizing device 13 between the two extremes is made through rotation of the stabilizing device 13 and movement of the center of rotation between positions A and B in figure 14. The center of rotation of the stabilizing device 13 is close to the center of the saw blade 14 (position A in figure 14) when the stabilizing device 13 and saw blade 14 are close to their operating positions and close to position B when the stabilizing device 13 is close to its transport position. The movement of the center of rotation may be continuous with the rotation or made sequential with the rotation e.g. a rotation only when the stabilizing device 13 is close to its operating position, thereafter a movement of the center of rotation and then again only rotation.

Finally the movement of the stabilizing device 13 between the two extremes may be composed of sub elements of movements from two or more of the previously described movements. Examples of such combination movements are:

Example 1 : From its highest (transport) position, the stabilizing device 13 is lowered using a linear straight down movement (figure 12), then it follows a pendulum movement (figure 13) until it is close to the saw blade 14 and finally it is rotated into operating position using a rotation movement (figure 14) with the center of rotation close to the center of the saw blade 14. The stabilizing device 13 is lifted using the reversed movement. Example 2: From its highest (transport) position, the stabilizing device 13 is lowered using a pendulum movement (figure 13) until it is close to the saw blade 14 and finally it is rotated into operating position using a rotation movement (figure 14) with the center of rotation close to the center of the saw blade 14. The stabilizing device 13 is lifted using the reversed movement.

The saw blade 14 is positioned in its highest position during transportation when the sawing machine 8 is moved to a new geographic position and a trench is not sawn during the transportation. The saw blade 14 is also in its highest position during saw blade 14 replacement. In this case the stabilizing device 13 with all ducts/cables 2, 3 remain in the trench 1 so that the trenching may continue after the saw blade 14 has been replaced. During saw blade 14 replacement, the saw blade cover which may be fitted over the saw blade 14 is opened over the whole side of the cover so that the whole saw blade 14 is accessible. The stabilizing device 13 is in its highest position during transportation and during the threading of all ducts/cables 2, 3 and during the start of the micro trenching. During start of the trenching and laying, the saw blade 14 is first lowered to its operating position and the sawing machine 8 is advanced around 1 - 2 m so that there is room in the trench 1 to lower the stabilizing device 13. There must also be room enough in the trench 1 for an anchor that holds the ducts/cables 2, 3 in place, so that they are not dragged after the sawing machine 8 when it starts to move forward.

To make the threading of ducts/cables 2, 3 easier the stabilizing device 13 may either be openable arranged or the stabilizing device 13 is fitted with an openable cassette so that ducts/cables 2, 3 can be easily laid down in their respective channels. An openable cassette that can be removed from and attached to the stabilizing device 13 will save time in some cases e.g. when the micro trenching is interrupted for some reason and restarted at a later time e.g. the next day from the same location. The removable cassette may be attached to the stabilizing device 13 by means of a hinge with a removable pivot. When the pivot has been removed, the cassette can easily be removed. The cassette can also be left in the micro trench 1 when the sawing machine 8 is moved to another location using the following method: remove the pivot and advance the sawing machine 8 a few centimeters so that the stabilizing device 13 without the cassette can be lifted. To reattach the cassette to the stabilizing device 13 the opposite maneuver is preformed.

Moreover, it has been realized by the inventors that the placement/installation of ducts/cables 2, 3 must be made before the sides of the trench collapses and before stones (or sand and dirt) and in particular stones larger than the width of the trench 1 are wedged into the sides of the trench and prevents the installation of the ducts/cables 2, 3 all the way down to the bottom of the trench 1. By achieving this time (and money) can be saved since the installation can be performed without unnecessary interruptions.

Therefore, the present machine 8 is arranged for sawing micro trenches 1 in an area. In this respect, the machine 8 comprises a saw blade 14, preferable circular in shape, for sawing/cutting the micro trenches 1. The produced micro trenches 1 are adapted for receiving ducts/cables 2, 3 which means that the micro trenches 1 has been given the proper dimensions.

The machine 8 also comprises a stabilizing device 13 arranged for stabilizing the walls of the micro trench 1 when placing ducts/cables 2, 3, and for this purpose the stabilizing device 13 is positioned immediately behind the saw blade 14 in the micro trench 1, so that the walls are stabilized until the ducts/cables 2, 3 have been placed/installed by means of guiding means 17 arranged on/in the stabilizing device 13.

For stabilizing the walls of the trench, the stabilizing device 13 comprises suitable stabilizing elements such as proper side elements which are arranged to "hold up" the walls until the ducts/cables 2, 3 have been installed in the micro trench 1. It is important that the stabilizing device 13 is positioned immediately behind the saw blade 14 so that the trench 1 sawn by the saw blade 14 is stabilized directly after it is produced so that it does not collapse, or that stones or debris fall to the bottom of the trench 1 before ducts/cables 2, 3 have been placed. Therefore is, according to an embodiment of the invention, the maximum distance between the saw blade 14 and the stabilizing device 13 larger than 0 mm but less than 20 mm. The dimension of the stabilizing device 13 is dependent on the size of the ducts/cables 2, 3, the number of ducts/cables 2, 3 to be placed at the same time, and the wanted depth for placement in the trench. However, the width of the stabilizing device 13 should be equal to or slightly less than the width of the sawing blade 14.

Furthermore, for achieving controlled and automatic placement of the ducts/cables 2, 3 the stabilizing device 13 also comprises guiding means 17 which guides the ducts/cables 2, 3 into the trench 1 in a controlled and ordered manner. The combination of stabilization and guiding has proved to reduce cost and time in an effective manner since the process of sawing and installing can be performed at the same time. The guiding means 17 are arranged on/in the stabilizing device 13 and hence the invention makes it possible to place the ducts/cables 2, 3 into the trench 1 while the trench 1 is stabilized by the stabilizing device 13. The ducts/cables 2, 3 can therefore be placed with high precision into the trench 1 (e.g. on the correct height in the trench 1) since the trench is "clean" as long as the trench is stabilized by the device 13.

The stabilizing device 13 may be made of any suitable hard material. The material should preferably be rigid, tough, hard and yet flexible so as to withstand stress during operation. The mounting of the stabilizing device 13 to the sawing machine 8 should have an amount of flexibility to prevent damage if the stabilizing device 13 is stuck in the trench 1. Steel or steel alloys are suitable since they can be given the right properties by alloying with different metals such as platinum and manganese. There is limited space in the trench 1 so the walls of the stabilizing device 13 have to be thin as possible so as to be able to accommodate all of the ducts/cables 2, 3 but still have the properties mentioned above. Steel alloys in the hardness of about 400-700 Brinell have proved suitable for these applications. It has also been realized that the stabilizing device 13 may be made of molded carbon fibre. Different parts of the stabilizing device 13 can be cast separately and assembled into a stabilizing device assembly 13.

According to an embodiment of the invention, the stabilizing device 13 has an inlet 11 and an outlet 12 for ducts/cables 2, 3, the inlet 11 and outlet 12 being connected to the guiding means 17. Preferably, the guiding means 17 are channels through which the ducts/cables 2, 3 are guided through the stabilizing device 13. When in operation, the inlet 11 is preferably above ground level 10 and vertically or close to vertically arranged while the outlet 12 is below ground in the micro trench 1 and horizontally or close to horizontally arranged in order to minimize wear and tear on the ducts/cables 2, 3. Therefore, the minimum horizontal distance at ground level 10 between the outlet 12 of the stabilizing device 13 and the saw blade 14 is slightly longer than the recommended minimum bending radius for the ducts/cables 2, 3 to be installed, which means that the minimum distance is dependent on the recommended minimum bending radius. This normally translates to somewhere between 100 to 500 mm measured at ground level 10, but other distances are possible. Further, the inlet 11, outlet 12 and guiding means 17 may together be removably attached on the stabilizing device 13 e.g. in the form of a removable cassette. By having a removable cassette for the guiding means 17, the installation time shortens in some cases as the time consuming task of inserting many ducts/cables 2, 3 into their respective channels may be avoided.

It has also been realized by the inventors that an operating depth for the stabilizing device 13 in the micro trench 1 shall be up to 50 mm less than an operating depth for the saw blade 14 according to an embodiment. This difference in operating depth between the saw blade 14 and the stabilizing device 13, decides how quickly the ground level 10 may change (i.e. go down). The saw blade 14 must have sawed the trench 1 deep enough so that the stabilizing device 13 never touches the bottom of the trench 1 in order to avoid the possibility of the stabilizing device 13 sticking to the bottom of the trench. This avoids unnecessary forces on the stabilizing device 13 and possible breakage. This may happen when the ground level 10 suddenly becomes much lower.

Moreover, according to yet another embodiment of the invention, the stabilizing device 13 and the saw blade 14 are arranged to be elevated and lowered independently of each other. This is advantageous when for example the saw blade 14 has to be changed due to wear or when another type of saw blade 14 is needed (e.g. one type for asphalt and another type for concrete). Further, the stabilizing device 13 may have to be replaced which may easily be performed if the two parts can be lowered and elevated independently of each other. Also, during shorter interruptions in the sawing operation the saw blade 14 is elevated, but the stabilizing device 13 must remain in the ground, since the need for stabilization of the trench still exists.

Figure 9 shows an embodiment of a machine 8 according to the invention. The stabilizing device 13 has a front part 18 and a back part 19, wherein the front part 18 is located immediately behind the saw blade 14. It can also be seen that the stabilizing device 13 has a section at the front part 18 that has a shape that is complementary to the shape of the saw blade 14, which in this particular case is circular. Thus, in this case the section at the front part 18 has a concave circular shape with the same radius, or close to the same radius, as the saw blade 14 and is placed as close as possible and less than 20 mm away from the saw blade 14. The reason for this is that the underground part of the stabilizing device 13 must be arranged so close to the saw blade 14 such that it is virtually impossible for dirt, stones and other debris to fall to the bottom of the trench or wedge between the sides of the trench. The guiding means 17 in this embodiment are channels inside the stabilizing device 13. The channels are illustrated with dotted lines in the figures.

The stabilizing device 13 may also be axe shaped in cross section at the front part 18 in the forward direction 9.

It has been realized by the inventors that if a micro trench 1 with other geometry (e.g. other width and/or depth) is wanted, the saw blade 14 and the stabilizing device 13 must be replaced. As previously stated the stabilizing device 13 must be complimentary in shape to the saw blade 14. Therefore if the saw blade 14 is changed to a saw blade 14 with different radius the stabilizing device 13 must be replaced with one with a concave shape with near the same radius.

When the saw blade 14 and stabilizing device 13 are replaced with ones with different measures, the lifting arms and/or their anchor points for lifting the stabilizing device 13 may have to be changed. This can be achieved by having adjustment screws or turnbuckles on the lifting arms and/or having other anchor points for the lifting arms prepared on the sawing machine 8.

Finally when changing the saw blade 14 diameter, it may be necessary to change the saw blade cover. The internal shape of the saw blade cover is optimized to the shape of the saw blade 14 in order to give maximum transport of the sawed up debris out through an opening in the front of the saw blade cover. This internal shape may have to be changed, when the saw blade 14 is replaced with one with different diameter, in order to get optimal transport of debris. Preferably, as mentioned above, the stabilizing device 13 has a maximum width in cross section that is equal to or slightly less than a width for the saw blade 14. The stabilizing device 13 must be wide enough to have room for the ducts/cables 2, 3 to be installed, but small enough so that it can be drawn forward in the sawed trench.

Another important aspect of the invention is that with the use of guiding means 17 an order of a plurality of ducts/cables 2, 3 is preserved when placed in the micro trench 1. This is very important when more than one duct/cable 2, 3 is placed at the same time. In one installation scenario, the duct/cable 2, 3 for a certain property is cut at a certain distance 15 beyond the property. It is important that this duct/cable 2, 3 is one of the ducts/cables 2, 3 on top of the pile of ducts/cables 2, 3 in the trench 1, so that it can be easily found. The duct/cable 2, 3 must be cut before the stabilizing device 13. Therefore it is important to know which one of all ducts/cables 2, 3 that enter the stabilizing device 13 will come out on top in the trench 1. Moreover, as the color of the duct/cable 2, 3 for a certain property is in many cases decided before the sawing begins, the order of the ducts/cables 2, 3 must be arranged so that the duct/cable 2, 3 having the correct color is cut to the correct length 15 for a certain property and comes out on top in the trench when that particular property is passed.

A method which allows simultaneous placement of a plurality of ducts/cables 2, 3 at the same time has a very high commercial value since the process of placement can be performed much faster than what has previously been know in the art. Therefore, according to this embodiment of the invention, the stabilizing device 13 has a plurality of guiding means 17 each guiding one or a few ducts/cables 2, 3 into the trench 1. For example, the stabilizing device 13 may comprise a plurality of channels so arranged that a known order is preserved, which means that an order of the ducts/cables 2, 3 out of the stabilizing device 13 is known form the order of ducts/cables 2, 3 into the stabilizing device 13, hence the order into and out of the stabilizing device 13 is related and known. This can e.g. be achieved by a one-to-one mapping between the inlet 11 and the outlet 12 of the stabilizing device 13, which means that they do not cross each other. The order of the ducts/cables 2, 3 should be arranged in such a way that one of the ducts/cables 2, 3 on top of the pile of ducts/cables 2, 3 in the trench 1 is always the one to be routed to the next location. Therefore, the ducts/cables 2, 3 entering the inlet 11 in the most rear position (in the sawing direction 9) will be among the uppermost ducts/cables 2, 3 out from the outlet 12, and vice versa, the most forward ducts/cables 2, 3 entering the inlet 11 will be among the lowermost ducts/cables 2, 3 out from the outlet 12. Branching micro trenches may be sawn before the main micro trench 7 is sawn as shown in figure 6 and 7 or the branching micro trenches may be sawn after the main trench 7 is sawn. The particular order in which the trenches are sawn may be decided to achieve the best flow during the installation. Each branching micro trench is intended for a final location for one of the ducts/cables 2, 3 from the main micro trench 7. When the main trench 7 is sawn and the ducts/cables 2, 3 are installed, the duct/cable 2, 3 about to become the top duct/cable 2, 3 is cut before entering the stabilizing device 13 at a certain distance 15 beyond the location of the respective branching trench, so that that duct/cable 2, 3 can be lifted from the main micro trench 7 and routed to its final location through the branch, see figure 10. If the cut is made correctly 15 the length of the duct/cable 2, 3 will be sufficient so that the duct/cable 2, 3 is long enough to reach the final location without splicing. In this way the ducts/cables 2, 3 are one by one routed to each passed location through the branches. Depending on the width of the trench 7 and the size of the ducts/cables 2, 3 there may be one or more ducts/cables 2, 3 side by side as the uppermost ducts/cables 2, 3 in the main trench 7. It is important that the duct/cable 2. 3 next to be routed to its final location is always one of the ones on top. To achieve this, when sawing the main trench 7 and placing a number of ducts/cables 2, 3, the duct/cable 2, 3 about to become one of the uppermost ducts/cables 2, 3, the one designated to the next predetermined location, is cut before it enters the stabilizing device 13 at a certain distance 15 after passing the corresponding branching trench, so that that duct/cable 2, 3 can be lifted and routed through the branching micro trench to its final location. The duct/cable 2, 3 should be cut at a certain minimum distance 15 after passing the corresponding branching trench, so that, when lifted from the main trench 7 and routed towards its final location, the length is sufficient to reach the final location without splicing.

If the stabilizing device 13 is designed with individual channels for the ducts/cables 2, 3 or with individual channels, each with room for a few ducts/cables 2, 3, it is easy to know which duct/cable 2, 3 will be on top in the trench 7 and thereby which duct/cable 2, 3 should be cut before the stabilizing device 13. Example of such stabilizing device 13 is shown in Figure 9. The stabilizing device 13 in this embodiment has a duct/cable 2, 3 inlet 11 and a duct/cable 2, 3 outlet 12 connected to each other by means of a plurality of channels as guiding means 17 (illustrated with dotted lines) for the ducts/cables 2, 3. The underground outlet 12 of the stabilizing device 13 may in an embodiment comprise a "matrix" (or vector) part so arranged that the channels are arranged in a matrix with n rows and m columns, thereby in a controlled way horizontally and/or vertically separating the ducts/cables 2, 3 when placing them in the micro trench 1.

So in summary: cutting; one after the other of the uppermost ducts/cables 2, 3, the one designated to a certain location, at a certain minimum distance 15 after its corresponding branch and thereafter lifting this duct/cable 2, 3 from the main trench 7 and routing it to its final location through the branch.

The machine 8 may further comprise at least one drum arranged for holding ducts/cables 2, 3 before placing them into the micro trench 1 via the stabilizing device 13. In this way easy access to the ducts/cables 2, 3 is achieved. Further, the machine 8 according to the invention may also comprise other suitable means, such as: one or more engine means for powering the saw blade 14, the stabilizing device 13 and/or driving means (e.g. drive train or wheels), communication means for wireless communication with e.g. a remote server unit, processing means, memory means, sensors, GPS means, vehicle means, display means for displaying information such as graphics, data base means, reading means for reading mechanical coding means on the saw blade 14, immobilizer, etc.

Regarding the powering of the saw blade 14 and/or the stabilizing device 13 this can e.g. be performed by means of direct mechanical driving, hydraulic driving or electric driving. Mechanical driving gives the highest power transmission ratio while electrical driving gives the lowest, so the former is preferred if high power is needed which often is the case.

Some road authorities require that the restoration and sealing of the micro trench 1 is made by re-asphalting a width of up to 500 mm. Therefore up to 250 mm of the surface layer LI on each side of the micro trench 1 must be removed. This normally implies an additional costly and labor intensive task. According to an embodiment of the present invention the machine 8, sawing and placing ducts/cables 2, 3 in the micro trench 1 is arranged with sawing devices on each side of the micro trench 1. These sawing devices saws/cuts through the surface layer LI in parallel with and on a certain distance from the micro trench 1. This is done at the same time as the machine 8 is sawing a micro trench 1 and placing ducts/cables 2, 3 in the micro trench 1. The sawing devices are arranged on the machine 8 using adjustable devices so that the distance to the micro trench 1 may be adjusted between 0-250 mm. The sawing depth of the sawing devices may also be adjusted using suitable devices between 0-150 mm. Later on, the surface layer LI between the two saw traces will be easy to remove. Figure 16 shows a cross section of a micro trench 1 that has been sawn by a sawing and laying machine 8 having sawing devices on each side of the micro trench 1 and where the asphalt layer LI between the saw traces, made by the two sawing devices, has been removed.

During transportation of the machine 8 the sawing devices are lifted completely above ground level 10. The sawing devices may be arranged with wheels in order to sense the top of the surface layer LI and to be able to saw to a predetermined depth below the surface.

Each one of the two sawing devices is powered by its own engine device. The sawing devices may be elevated and lowered independently of saw blade 14 and stabilizing device 13. The sawing devices have protective covers over their saw blades, which may be diamond saw blades. The sawing devices are arranged on the machine 8 on each side of the micro trench 1, in parallel with and behind the saw blade 14, sawing the micro trench 1.

The inventors have also realized that there may be a need for a sword shaped saw blade 14 having a saw chain or a saw wire driven around this sword saw blade 14 by an engine device. Such sword saw blade 14 with its saw chain or saw wire may be used for sawing through the surface layer LI and into the bearing layer below. Such sword shaped saw blade 14 then replaces the circular saw blade 14. The sawing surfaces on such saw chain or saw wire may have on suitable places segments/pearls containing diamonds and thereby having the same sawing properties as a circular diamond saw blade 14. The stabilizing device 13 with guiding means 17 for ducts/cables 2, 3 is positioned immediately behind and as close as possible to the sword saw blade 14 in the same way as with a circular saw blade 14. The front part 18 of the stabilizing device 13 shall in both cases have a shape that is complementary to the shape of the respective saw blade 14. Instead of wheels on the machine 8, the machine 8 may be arranged with caterpillar tracks. Such caterpillar tracks may be considered as "a private road" for the bearing wheels supporting the caterpillar tracks. Caterpillar tracks have much larger contact surface to the ground, which means that the weight of the machine 8 will be spread out over a larger area compared with wheels and thereby the ground pressure will be much lower per unit area.

The inventors have also realized that there might be a need for allowing the saw blade 14 and the stabilizing device 13, while keeping their mutual relative positions, to move forward or backward in the sawing direction 9 even though the machine 8 stands still. This may be important e.g. when the machine 8 is close to an obstacle, such as a wall, fence, hole in the ground, grass surface, side walk or other obstacle preventing the machine 8 to move. The above mentioned function allows the saw blade 14 and stabilizing device 13 to keep sawing and laying ducts/cables 2, 3 up to 2000 mm although the machine 8 stands still. This function makes it possible to saw all the way up to or from an obstacle. Elevation and lowering and the above described horizontal movements of the saw blade 14 and the stabilizing device 13, with a stationary machine 8 may be controlled by one or a number specially adapted engines, driving devices and movable axes.

Example 1 : Sawing up to an obstacle. The machine 8 is sawing and placing ducts/cables 2, 3 in the micro trench 1 up to an obstacle in front of the machine 8 with the saw blade 14 and stabilizing device 13 in their normal positions. The machine 8 stops at the obstacle and stands completely still while the saw blade 14 and stabilizing device 13 is allowed to continue to saw and place ducts/cables 2, 3 all the way up to the obstacle. Thereafter the saw blade 14 and the stabilizing device 13 are lifted to their transport positions.

Example 2: Start from an obstacle behind the machine 8. With the saw blade 14 and the stabilizing device 13 lifted above ground level 10, the machine 8 is backed as close to the obstacle as possible. With the machine 8 standing completely still, the saw blade 14 and the stabilizing device 13 are then moved as close to the obstacle as possible. Thereafter the saw blade 14 is lowered to sawing depth and is allowed to saw forward a suitable distance while, at least in the beginning the machine 8 is not moving. Then the stabilizing device 13 with its ducts/cables 2, 3 is lowered into the micro trench 1 and the machine 8 can start moving forward in the normal manner.

Micro Trenching Technique (MTT)

A thorough understanding of the MTT method is needed. Figure 1 shows a flow chart of a MTT method for placing at least one duct/cable 2, 3 below a road surface layer LI in an area comprising the steps of:

- sawing a micro trench 1 in the area through the first layer LI into the second layer L2;

- placing at least one duct/cable 2, 3 in the micro trench 1 so that the at least one duct/cable 2, 3 is placed below the first layer LI; and

- filling the micro trench 1 so as to restore the area.

Figure 3a and 3b schematically shows a cross section of an area in which ducts 2 are placed in a micro trench 1. The area in figure 3a and 3b is a three dimensional region of a typical roadway area, wherein the area comprises a first layer LI being a surface layer such as asphalt or concrete, and a second layer L2 being a bearing layer for the first layer LI and usually consisting of gravel, sand and earth. The second layer L2 is naturally located below the first layer LI as shown in figure 3a and 3b.

The sawing step involves: sawing the micro trench 1 through the first layer LI into the second layer L2, which means that the micro trench 1 is sawn as shown in figure 3a and 3b. The micro trench 1 is sawn so deep that at least one duct/cable 2, 3 is placed in the micro trench 1 below the first layer LI (i.e. all installed ducts/cables 2, 3 are placed below the first layer LI). Using the present method all ducts 2 and cables 3 for fibre optic networks can be placed deep enough so that they are safe if the surface layer LI is removed and/or replaced, e.g. when repairing the road.

Thereafter, the at least one duct 2 and/or a communication cable 3 is placed in the micro trench 1. The duct 2 is a duct arranged to hold "air-blown fibre" (so called EPFU) or fibre cables. The duct/s 2 and/or the communication cable/s 3 are placed in the micro trench 1 so that they are entirely positioned below the first layer LI .

Finally, the micro trench 1 is filled with a suitable filling material 6 so that the roadbed is restored. The filling material 6 may be sand or any other material with suitable properties. A filling material 6 that is liquid at the time of the filling 6 and which later cures and becomes highly resistant against compression forces is a preferred filing material. The micro trench 1 is filled with the filling material 6 to a suitable level, and if needed the filling material 6 is thereafter packed with a compactor that fits the width w of the micro trench 1.

Finally, the micro trench 1 is sealed using a sealing material, such as bitumen, in order to get a water tight sealing. If a water tight sealing is not needed, patching may also be made with cold asphalt which is a simple and cheap method of restoration. A suitable amount of cold asphalt is simply poured and scraped into the micro trench 1, and thereafter compacted to a smooth and hard surface. Any excess asphalt can then be collected and removed.

The sealing step may according to a preferred embodiment involve the steps of:

- sealing the micro trench 1 flush to a bottom 5 of the first layer LI with a first sealing SI; and

- sealing the micro trench 1 flush to a surface 4 of the first layer LI with a second sealing S2.

Figure 4 shows the above described embodiment. The surface 4 and the bottom 5 of the first layer LI are indicated in figure 4. In order to obtain a sealed repair with high adhesion it is recommended to pour hot bitumen or bitumen mix when sealing the micro trench 1. However, other material such as concrete or polymer modified asphalt will work.

The first sealing SI is put down to seal the micro trench 1 substantially flush with the bottom 5 of the first layer LI so that the micro trench 1 can be cleaned with a high-pressure washer to remove any residue of sand from the asphalt/concrete edges. After washing, the micro trench 1 may be dried and pre-heated using a propane burner and finally, the micro trench 1 is filled flush with the top surface 4 of the first layer LI using a suitable sealant such as a hot crack sealant based on bitumen. According to yet another embodiment, the micro trench 1 is cut with a disc cutter/sawing machine 8 having a diamond coated saw blade 14. Such a diamond coated saw blade 14 can easily saw through even the hardest materials, such as stone or concrete, and has proved very useful in the present application since the sides of the micro trench 1 becomes exceptionally straight, clean and easy to restore. Prior art methods to cut micro trenches, such as using a saw blade with tungsten carbide teeth, creates small cracks in the edges of the micro trench that will make complete sealing afterwards much harder and more expensive compared the present method.

The micro trench 1 is preferably cut/sawed with a modified so-called road-saw 8 (sawing machine 8) having a diamond coated saw blade 14. To further optimize the performance of the road saw in the present application, the inventors have realized that one or more of the following improvements are useful and should be considered as embodiments:

• Change in rotational direction of the saw blade 14 to so-called "up-cut" for improved transport of cuttings;

• Modified cover for the saw blade 14 and a front outlet to optimize the transport of cuttings and reduce spreading of dust and leave the micro trench 1 clean and ready for laying ducts/cables 2, 3;

• Stabilizing device 13 as shown in figure 8 and 9 with one or more guiding means 17 for ducts/cables 2, 3 immediately after the saw blade 14 so that micro trenching and placing of ducts/cables 2, 3 can be carried out in one continuous process. In case the stabilizing device 13 has guiding means 17 for a plurality of ducts/cables 2, 3, these guiding means 17 should be arranged so the outlets 12 from the stabilizing device 13 are placed on top of each other in such a way that the order of the ducts/cables 2, 3 from the inlet 11 into the stabilizing device 13 and out into the micro trench 1 is preserved;

• Trailer drawn by the road saw with holders for drums for ducts/cables 2, 3 and warning tape with tracking wire;

• Servo controlled by a sensor to automatically keep the saw blade 14 vertical on uneven surfaces. (E.g. when the drive train (wheels or caterpillar tracks) on one side are on the side walk and the drive train on the other side are on the road.) • Sensor sensing the temperature of the saw blade 14 and automatically adds more cooling water if the temperature of the saw blade 14 increases or alternatively lower the rotation speed. Cooling water is applied near the center of and on both sides of the saw blade 14

· Gear box so that the peripheral speed of the saw blade 14 can be kept constant when changing the diameter of the saw blade 14.

Figure 8 shows an embodiment using a sawing machine 8 comprising a saw blade 14 arranged for up-cut. Up-cut is defined as the rotating direction of the saw blade 14 in relation to the sawing direction 9 as shown by figure 8. All known sawing machines have the opposite rotating direction. By changing the rotating direction of the sawing machine 8 to up-cut helps to remove the cut material from the micro trench 1, thereby providing a "clean" micro trench 1. Further, the sawing machine 8 comprises a stabilizing device 13 arranged immediately behind the saw blade 14, wherein the stabilizing device 13 has at least one guiding means 17, such as channels, for guiding the duct/cable 2, 3 when placed in the micro trench 1 immediately behind the saw blade 14. If a plurality of ducts/cables 2, 3 is placed at the same time, the stabilizing device 13 is arranged to be able to place the ducts/cables 2, 3 in preserved order. This may be achieved by having individual channels for the ducts/cables 2, 3 in the stabilizing device 13 so that the order of the ducts/cables 2, 3 will be maintained through the stabilizing device 13. Thereby, it is possible before the ducts/cables 2, 3 enter into the stabilizing device 13 to identify which duct/cable 2, 3 will come out on top in the micro trench 1 and thereby making it possible to know which duct/cable 2, 3 to cut for each final location, see figure 10.

According to an embodiment, the depth d of the micro trench 1 should be larger than the depth of the first layer dl together with the height d2 of at least one duct 2 or at least one communication cable 3, i.e. d > dl + d2 which means that the depth d of the micro trench 1 is larger than the height of the first layer dl plus the combined height of one or more ducts 2 and/or communication cables 3. As can be deduced from figure 3a, 3b and 4, the above mentioned relation holds. However, costs increase with increased depth d of the micro trench 1. Therefore, the micro trench 1 should not be deeper than necessary. Normal depth d of the micro trench 1 can be around 400 mm, and unlike the width w of the micro trench 1, the depth d can often be adjusted continuously. The sawing depth can therefore be reduced gradually as the number of ducts 2 laid in the micro trench 1 is reduced.

Further, the micro trench 1 should not be wider than necessary, since a wider micro trench 1 is more expensive than a narrow micro trench 1. On the other hand a narrower micro trench 1 can make it more difficult to install the ducts/cables 2, 3, so there is an optimal width of the micro trench 1, since e.g. if the micro trench 1 is too narrow, all ducts/cables 2, 3 will be piled on top of each other so that the depth of the top duct/cable 2, 3 will be too shallow.

From the above discussion, the inventors have through tests realised that suitable dimensions for a micro trench 1 should have a depth d between 200 - 500 mm (and preferably 300 - 500 mm) and a width w between 10 - 30 mm (and preferably 15 - 25 mm) according to an embodiment for installation efficiency and low cost. Further, with these dimensions minimum disruption of traffic is possible when placing ducts/cables 2, 3 since traffic can pass over an open micro trench 1. Furthermore, with reference to the flow chart in figure 2, according to another embodiment, the method for placing at least one duct/cable 2, 3 comprises the steps of:

- scanning an area by means of a ground penetrating radar; and

- identifying obstacles in the area using data generated by the ground penetrating radar,

- sawing a micro trench 1 in the area through the first layer LI into the second layer L2;

- placing at least one duct/cable 2, 3 in the micro trench 1 so that the at least one duct/cable 2, 3 is placed below the first layer (LI); and

- filling the micro trench 1 so as to restore the road surface.

It should be noted that the steps of scanning and identifying are performed before the other steps in the method according to this embodiment.

According to this embodiment, the area is scanned by means of a ground penetrating radar device, such as a GEO-radar or any other suitable equipment. Thereafter, possible underground obstacles in the area, such as sewer pipes, electrical cables, construction structures, etc. are identified using information generated by the ground penetrating radar device. The scanning and identifying steps means that when performing the subsequent sawing step it may be avoided to accidentally cut/damage obstacles in the area which may result in delay and extra cost in the micro trenching process. After sawing a micro trench 1 in the scanned area, at least one duct 2 and/or a communication cable 3 is placed in the micro trench 1. Finally, the micro trench 1 is filled with a suitable filling material 6 so that the road surface is restored.

The method may also involve the step of: installing or blowing fibre or fibre cable in one or more ducts 2 if ducts were placed in the micro trench 1.

It should also be noted that the method described above also may comprise the step of: making one or more branching points connected to the micro trench 1. Preferably, the branching points may be made by means of a diamond coated core drill or a hand-held sawing machine with a diamond coated sawing chain or disc. As for this described embodiment the method may also comprise the further step of: boring one or more channels from the branching points to one or more houses using controlled or guided boring. It is important that channels are bored below the first layer LI in the second bearing layer L2. Ducts/cables 2, 3 are thereafter installed in these channels when the drill is pulled back.

Different aspects concerning the layout of micro trenches, branching points and channels, and strategies of cutting, branching, etc, in relation to and incorporated in the present method will be discussed in the following description.

Layout

Figure 5 shows a typical logical structure of a Fibre To The Home (FTTH) network in a residential area, where "D" is a distribution node and "F" is a splicing point where larger fibre cables are spliced to smaller ones (or in case of a PON network where optical splitters are placed). The network between a distribution node D and a splicing point F is called distribution network and the network between the splicing point F and the individual homes is called access network. Both the ducts/cables 2, 3 for the distribution network and for the access network can be installed using the present method.

A residential area being constructed with FTTH is normally divided into a number of smaller residential subareas. Somewhere in the residential area or outside of the residential area there must be a site where optical panels and electronics needed to form a so-called distribution node D are housed. The distribution node D can be housed in an existing building or in a small dedicated built building or in a large ground cabinet. Each distribution node D may contain electronics and optical panels for anywhere between a few hundred households up to several thousand households. The size of the area to be built from a single distribution node D can be adjusted within wide limits and depends primarily on practical considerations, such as space in the distribution node D, difficulties with management of a large number of smaller distribution nodes D, etc. This concept can also be adapted for any number of fibres per household.

There are two main types of FTTH networks: point-to-point-networks and point-to-multipoint networks. In a so-called point-to-point-network, the distribution node D contains the other ends of all fibres that originate from the households in the residential area. If e.g. a residential area with 500 households is being equipped with 2 fibres per house, there will be 1000 incoming fibres to the distribution node D. The distribution node D should preferably have a central location in the area being built as shown in figure 5.

The fibre structure of a point-to-multipoint-network or a so-called Passive Optical Network (PON) is more or less the same. The difference being that the number of incoming fibres to the distribution node D in this case equals the number of households divided by a factor (e.g. 8, 16, 32, etc. depending on the chosen type of the so called splitter). The examples in the continuing discussion are made assuming that a point-to-point-network is being built. However, described methods also apply to a PON if only the distribution cables are scaled accordingly.

Viewed from the distribution node D, distribution cables extend out to splicing points F in manholes or cabinets. Distribution cables are normally designed for the number of households in the area plus 10 % spare so that in the future, newly built buildings easily can be added to the network. In a point-to-point-network, if e.g. a splicing point covers an area with 22 houses and the requirement is two fibres per house, then 48 fibres from the distribution cable are needed. Fibres from the distribution cables are spliced in the splicing points F to fibres from the access cables. These access cables then extend to each one of the houses being connected.

How many houses a splicing point F serves mainly depends on economic issues. If the covered area is too large, this will increase the average length of access cables to the houses, which increases costs. On the other hand, if the covered area is too small the cost for each house will rise in relation to its share of splicing point F and distribution cable. Hence, there is an optimum size to the residential area where the cost is the lowest. The number of houses that would minimise the cost depends mainly on the topography of the residential area and how large the plots of land are on which the houses are standing, but a rule of thumb is that an optimum size is normally somewhere between 16 and 48 houses from each splicing point F.

If micro trenching is carried out using a disc cutter according to an embodiment, the splicing point F should be placed centrally in each residential subarea, with e.g. around 22 houses. The splicing point F can be physically realised in a street cabinet or in a manhole by the roadside. Then, typically 10-12 ducts 2 extend from the ground cabinet or manhole each way along the road. Each of these ducts 2 then extends into each of the houses. Finally, access cables are blown into each of these ducts 2.

Strategy when sawing

Usually, residential areas have houses on both sides of a road, and this situation can be tackled in one of two different ways: either micro trench in the roadside on both sides of the road and connect the houses to the closest micro trench, or micro trench on only one side of the road or in the middle of the road and connect houses on both sides to this single micro trench. However, to minimize the number of micro trenches across the road, branching micro trenches are made to a boundary between two properties (houses) on the opposite side of the road according to an embodiment. Then a duct/channeling tube 2 is placed in the branching micro trench to each one of the two properties. In this way, a micro trench across the road need only be made for every second property on the opposite side of the road. Micro trenching across the road for every second property is a cheap and cost effective method.

Branching off a main trench

Branching off from a main micro trench 7 (a main micro trench 7 is defined as a micro trench 1 along a road) can be carried out in a number of ways. The branches may be sawn either before as shown in figure 6 or after the main trench 7 is sawn. Both methods are best done at about a 45° angle from the main micro trench 7 in order to obtain a large radius curve for the ducts/tubing 2. The branches may cross the location of the main micro trench 7 or go "flush" with the main trench 7. When the main micro trench 7 is sawed and the ducts/channelling tubes 2 are laid it is easy to one by one route one of the uppermost tubes through each of the sawed branches up to each residence, as shown in figure 10 and to the right in figure 6.

An alternative method of branching is to first bore a hole at each branching point with a suitably sized core drill. The main micro trench 7 can then be sawed along all these holes in the same manner as described above as shown in figure 7. This method is suited both to making the house connections with a branching micro trench sawn in the way described above as well as making house connections with controlled/guided boring. An alternative method of branching is to first make a hole at each branching point. The holes may be made using a suitably sized core drill (for a round hole) or using a hand tool with a diamond saw blade or chain (for a rectangular hole). The main micro trench 7 can then be sawn along all these holes in the same manner as described above and as shown in figure 7. This method is suited both to making the house connections with a branching micro trench sawn in the way described above as well as making house connections with controlled boring. Controlled boring is sometimes preferred for making the house connections, because it avoids (e.g. goes under) obstacles like fences, hedges, trees, etc. However, another piece of expensive machinery (core drill) is needed at the installation site. Finally, it should be understood that the present invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.