When working on very large structures, the positioning and operation of machine tools can become very complex. For example, in ship building, often very large metal plates need to be welded together using specialist welding tools and positioning and operation of these tools is highly complicated. Various types of machines are known that can be used to carry such tools, but there is a need to provide a machine that can work continuously in a straight line while carrying an operational tool. It is therefore an object of the invention to improve upon the known art.

According to the present invention, there is provided a continuous crawler comprising two platforms, each platform comprising two sliding carriages, each sliding carriage comprising engaging means for engaging a surface below the continuous crawler and each sliding carriage arranged to slide forwards and backwards relative to their respective platform, driving means for driving the sliding carriages backwards and forwards and control means for controlling the engaging means and driving means and arranged to drive one sliding carriage on each platform backwards relative to the respective platform while the engaging means on these sliding carriages are engaging the surface and simultaneously drive the other sliding carriage on each platform forwards relative to the respective platform while the engaging means on these sliding carriages are not engaging the surface.

Owing to the invention, it is possible to provide a continuous travelling machine with consistent adhesion action. A portable vacuum or electro- magnetic powered machine is provided that can be attached to a work piece instead of the work piece being brought to the machine. Preferably using vacuum suction or electro-magnets to enable gripping of a surface, continuous movement of machine to progress in desired direction is provided, for example for use along a join between two plates. The crawler can be attached to a surface or any number of adjacent surfaces and progress along them at a continuous and constant or variable speed. The machine needs to be able to travel on a horizontal plane or at any angle between these two planes. The continuous crawler is suitable for working on a horizontal surface and can also work on surfaces that are at an angle, even surfaces that are vertical and beyond. If a steep angle is present such as in the case of a vertical surface, then tow rope or chain secured above and below the crawler and to the crawler can be used to assist in the travel of the crawler and in the adhesion of the crawler to the surface. At the too, the rope or chain can be secured with a hook and the crawler uses the rope or chain to pull itself upwards in addition to the crawling via the engaging means on the underside of the crawler.

The machine preferably comprises a pair of platforms each carrying a pair of sliding carriages which in turn carry one or more suction cups with internal cleats or electromagnets which are located via shoulder screws or similar to the sliding carriages. Each sliding carriage is supported by linear "V" bearings and rails (or similar) which allow them slide relative to the platform. The platforms are kept at a constant distance from the work piece by supporting wheels, rollers or skids. The sliding carriages are driven backwards and forwards relative to the main base plate by screw drives (or similar) which pass through a drive nut or rack. These screw drives are preferably connected to electric motors, however hydraulic or pneumatic motors can be used.

The second platform of the same design is connected to the first platform by round shafts (or similar) and the screw drives are synchronously connected by notched drive belts, chains or shafts so that each pair of sliding carriages travel at the same speed and move the same distance. Alternately, the second platform may have its own electric motors so that by varying the speed of the sliding carriages between the two platforms, some amount of skid steer may be obtained.

Advantageously, a work head is carried on a separate carriage which slides in the x axis on linear bearings on two or more shafts that are in turn able to move relative to the machine in the y axis on linear bearings on round shafts. The x-axis is considered to be the direction of travel of the crawler and the y-axis is the direction perpendicular to this across the crawler. The third axis z can be floating or controlled by the work head spindle position. All three axes can be driven by ball screws or linear drives with CNC control for compensation and completion of weld controlled by a laser which monitors the join between two plates and adjusts welding head position to suit.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a continuous crawler,

Figure 2 is a section through a platform of the continuous crawler, Figure 3 is a view from below of the continuous crawler,

Figure 4 is a view from above of the continuous crawler,

Figure 5 is a top view and side view of the crawler in use, and

Figure 6 is a schematic view from above of the continuous crawler.

Figure 1 shows a schematic view of the continuous crawler 10. The continuous crawler 10 comprises two platforms 12, each platform 12 comprising two sliding carriages 14 and a frame 24 connected between and to each platform 12. The frame 24 comprises two pairs of beams 23, each beam 23 connected by a round bar 25. Each platform 12 is of elongate form and the two platforms 12 are substantially parallel on their longitudinal axes. Each sliding carriage 14 comprises engaging means 16 for engaging a surface below the continuous crawler 10 and each sliding carriage 14 is arranged to slide forwards and backwards relative to their respective platform 12. Each engaging means 16 comprises a pair of vacuum cups 30 that can be switched to engage or disengage the surface.

The crawler 10 also comprises driving means 20 for driving the sliding carriages 14 backwards and forwards and control means for controlling the engaging means 16 and driving means 20. The driving means 20 comprises motors 36 and screw drives 34. Belts 46 connect the screw drives 34 on the different platforms 12. Each sliding carriage 14 is connected to a screw drive 34 via a rectangular cross-section block 21. The control means is arranged to drive one sliding carriage 14 on each platform 12 backwards relative to the respective platform 12 while the engaging means 16 on these sliding carriages 14 are engaging the surface and simultaneously drive the other sliding carriage 14 on each platform 12 forwards relative to the respective platform 12 while the engaging means 16 on these sliding carriages 14 are not engaging the surface. Once the sliding carriages 14 have reached the limits of their movement this process is reversed.

Essentially, the crawler 10 moves forward by using the vacuum cups 30 to attach itself to the surface below. There are eight vacuum cups 30 on the crawler 10, two on each of the four sliding carriages 14. When the crawler 10 is moving forward, four of the vacuum cups 30 are engaged with the surface. Two of the four vacuum cups 30 so engaged are provided on one sliding carriage 14 and the other two of the four vacuum cups 30 so engaged are provided on a different sliding carriage 14, on the opposite side of the crawler 10. The relative movement between the sliding carriages 14 that are engaged to the surface 18 and the platforms 12 move the crawler 10 forward.

Figure 2 shows a section through a single platform 12. The platform 12 has two sliding carriages 14 which are each provided with engaging means 16 that engage the surface 18. The engaging means 16 includes a vacuum cup 30 that has support cleats. The left-hand vacuum cup 30 in Figure 2 is engaging the surface 18 and the right-hand vacuum cup 30 is not engaging the surface 18. This is the continuous working configuration of each of the platforms 12, with one sliding carriage 14 having its engaging means 16 engaging the surface 18 and the other sliding carriage having its engaging means 16 not engaging the surface 18, apart from a short period of overlap, when all of the engaging means 16 will be in operation at the same time. So at the point of switch over between the sliding carriages 14, both of the vacuum cups 30 in Figure 2 will be engaged to the surface 18. Only after this overlap point will the left-hand vacuum cup 30 disengage and the respective sliding carriage 14 begin its movement back to the front of the platform 12. Each platform 12 is provided with supporting means 32 in contact with and for supporting the platform 12 on the surface 18. In this example the supporting means 32 are support wheels 32 that are in compression during the operation of the crawler 12. The sliding carriages 14 are mounted on linear bearings 38 on V rails and shoulder screws 40 connect the vacuum cups 30 to the sliding carriages 14. Vacuum pipes 42 supply the vacuum to the vacuum cups 30. When the vacuum is on, the vacuum cup 30 pulls down and the cleats provide support and traction. The shoulder screws 40 pull down on the sliding carriage 14. The pull down is transmitted through the V bearings 38 which pull the platform 12 down towards the surface 18.

When the vacuum is turned off, the vacuum cup 30 rises to a relaxed position and the contact between the surface 18 and the cleats inside the cup 30 ceases. The cup 30 is able to slide across the surface 18 with just the outer lip of the vacuum cup 30 in contact with the surface 18. Each sliding carriage 14 moves relative to the platform 12. The sliding carriage 14 that is fixed relative to the surface 18 is effectively moving the whole crawler 10 forward through the relative movement between the sliding carriage 14 and the platform 12. At the same time the other sliding carriage 14 is moving forward to prepare to swap roles with currently fixed sliding carriage 14.

Figure 3 shows a view from underneath the crawler 10. The platforms

12 can be seen that are either side of the frame 24, which is comprised of the four beams 23 and the two bars 25. The eight vacuum cups 30 can be seen, which are mounted in pairs on respective sliding carriages 14. The sliding carriages 14 slide relative to the platform 12 to which they connect. The sliding carriages 14 work in pairs, with one sliding carriage 14 on each platform 12 paired with a sliding carriage 14 on the other platform 12. This ensures that when the four of vacuum cups 30 are engaged to the surface 18, two of the four are on each side of the crawler 10.

The frame 24 is connected between and to each platform 12. The continuous crawler 10 also comprises a work head 26, which is connected to the main base plate 24. A work head carriage 28 carries the work head 26, which is mounted on the work head carriage 28 and the work head carriage 28 is arranged to slide forwards and backwards relative to the frame 24. The work head carriage 28 can also move in the perpendicular direction. The work head 26 carries whatever tool is being used by the crawler 10, such as a welding tool that is welding together two plates that form the surface 18 on which the crawler is working.

The modus operandi of the work head 26 is that the machine 10 is placed on the material 18 to be joined (or machined) and the work head 26 is positioned outside the workpiece 18. The machine 10 travels to the other end of the material 18 where it stops. The work head 26 can continue travelling on the shafts 44 and pass out of the material 18 to complete the weld. In this way, the welding process can be completed in a straight line of essentially infinite distance, since the crawler 10 will continue moving forward in a straight line over the material 18 that is being welded by the tool on the work head 26.

Connected to the work head 26 is a laser 27, which is used to keep the work head 26 in the correct position as the crawler 10 moves forward. Small errors in the position of the work head 26 relative to the job underneath (such as a line of welding) can be corrected by moving the work head 26 in the y- axis. The x-axis is considered to be the direction of travel of the crawler 10. Motors 52 are driven based on feedback from the laser 27 and will move the work head 26 on the y-axis (left and right in the orientation of Figure 3). Motor 54 can be used to move the work head 26 in the x-axis.

Figure 4 shows the crawler 10 in the same configuration as in Figure 3 but viewed from above. The platforms 12 are shown either side of the frame 24, which comprises the four beams 23 and the two bars 25 and supports the work head carriage 28 on the shafts 44. Two motors 36 can be seen, which control the motion of the sliding carriages 14 through screw drives 34, which can also be seen in the perspective view of Figure 1. Each motor 36 drives two sliding carriages 14, one on each of the two platforms 12. Belts 46 connect across the crawler 10 to connect together the pairs of sliding carriages 14, via the screw drives 34. The turning of the motors 36 moves the sliding carriages 14 forwards and backwards relative to the platforms 12. The modus operandi of the travelling machine 10 uses synchronous drives. The machine 10 is placed on the workpiece 18 and is controlled by a PLC, CNC or similar. All sliding carriages 14 are set to the front position of the direction in which the machine 10 is to travel. A vacuum is applied to one pair of vacuum cups 30 on each platform 12 and then the screw drive 34 on the same sliding carriages 14 begins to turn and this draws the machine 10 forwards. Just before the moving sliding carriages 14 reach their end point, the screw drive 34 on the currently stationary sliding carriages 14 begins to turn and then vacuum is applied to vacuum cups 30 on this sliding carriage 14. At this point all vacuum cups 30 are attached and driving the machine 10.

The vacuum is now removed from vacuum cups 30 on the first sliding carriages 14 and then the drive screw 34 for these sliding carriages 14 is reversed at a higher speed enabling the sliding carriages 14 to be returned to the front position in time to repeat the process when the other pair of sliding carriages 14 are near the end point. The process repeats until the machine 10 has moved the required distance. Independent drives can be used and therefore if all drive screws 34 are fitted with separate motors 36 a certain amount of skid steer is possible by accelerating one platform 10 in relation to the other.

The machine 10 must have enough adhesion to the surface(s) 18 to keep a tool or manipulator in contact or in a relatively constant position with the surface(s) 18 and resist pressure from that tool or manipulator in relation to the surface 18, so that continuous and constant or variable speed or position of the machine in not affected. The machine 10 may have a sighting device to enable the machine 10 to be aimed at a predetermined destination. The machine may also have a secondary detector to adjust and/or correct the position of the work head 26 and the tool relative to the surface(s) whilst the machine is travelling. As mentioned above, with respect to Figure 3, this can be in the form of a laser attached to the work head 26.

Figure 5 illustrates the crawler 10 in operation welding two sheets 18a and 18b together. A laser target 48 is placed at the end of join between the two workpieces 18a and 18b and a laser beam 50 is used to sight the target 48 and ensure that the crawler 10 can be aimed along the line of travel that is intended. A laser sighting device on the crawler 10 provides alignment of the machine 10 between the two workpieces 18a and 18b. The laser sighting device is mounted to the front of the machine 10 and is accurately aligned with the centre line of direction of travel of the machine 10. Before the machine 10 starts moving, the machine 10 is positioned so that the laser beam 50 is directed at the target 48 at the end of the workpiece 18 so as to align the route of the machine 10 along the join of the workpieces 18.

The machine 10 incorporates a work head 26 upon which a tool such as an FSW tool, a milling cutter, a drill, a flame cutter, a laser cutter, an engraving cutter, a shot blaster or similar tool may be mounted. The machine 10 can be used vertically (for example on ships), horizontally, possibly inverted, possibly underwater. The type of FSW tools that are likely to be used would be of the Bobbin design. The sequence of turning on and off the vacuum of the suction cups or electromagnets combined with the timing of the motors is the key to the progressive constant movement.

Figure 6 shows the crawler 10 schematically. The frame 24 is in the centre of the two platforms 12. Underneath each platform 12 are two sliding carriages 14 that each carry two vacuum cups 30. In the preferred embodiment, two motors 36 are provided on one of the platforms 12 that each drive the motion of two of the sliding carriages 14. Each motor 36 drives one sliding carriage 14 on each platform 12. Control means 22 is provided that controls the motors 36 and the vacuum cups 30 in order to operate the crawler 10. Power is supplied to the crawler 10 by a cable from an external power supply plus an airline to supply air to ejector vacuum pumps.

Detection units in the form of micro-switches are provided on the platform 12 that carries the motors 36. These detection units monitor the position of the sliding carriages 14 under that platform 12. This information is supplied to the control means 22 which uses the information from the detection units to determine when to switch over from one pair of sliding carriages 14 to the other pair of sliding carriages ^4. The detection units detect when the sliding carriages 14 are reaching the end of their maximum allowable movement, which is determined by a slot in the platform through which the vacuum pipe 42 is connected to the vacuum cups 30 of the sliding carriage 14.

The principle of the operation of the crawler 10 is that one pair of sliding carriages 14 are engaged with the surface 18 below the crawler 10 while the other pair of sliding carriages 14 are disengaged and returned from the back position to the front position at a speed faster than the engaged pair are moving relative to the platform 12. Once the currently moving pair of sliding carriages have reached or are near to their maximum movement, the control means will swap over the roles of the two pairs of sliding carriages 14. This ensures that there is continuous forward movement of the crawler 10 and that it is engaged to the working surface 18 at all times.

The control means 22 is arranged to engage the engaging means 16 that are currently disengaged prior to disengaging the engaging means 16 that are currently engaged. This ensures that there is an overlap in the suction provided by the engaging means 16 so that the crawler 10 is always gripping the surface 18 below. For a short period of overlap, all of vacuum cups 30 of the engaging means 16 will be engaged with the surface 18. Only once this period of overlap has ended will the control means 22 remove the suction from one pair of engaging means 16 and move forward the sliding carriages 14 that are carrying these vacuum cups 30 that have just disengaged the surface 18.