WO2009077381A1

WO2009077381A1 - Carriage for travelling on a ferromagnetic workpiece

Info

Publication number: WO2009077381A1
Application number: PCT/EP2008/067103
Authority: WO
Inventors: Børge ØLLGAARD
Original assignee: Vestas Wind Systems A/S
Priority date: 2007-12-14
Filing date: 2008-12-09
Publication date: 2009-06-25

Abstract

A carriage (1) adapted for travelling on a ferromagnetic workpiece (2), said carriage (1) comprising a main body (3) being provided with a plurality of rollers (4) and at least one magnet (5). The carriage (1) further comprises a tool holder (6) for a tool (7). To provide a simple and cost effective carriage, the carriage (1) comprises a support (9) adapted for holding the carriage in a substantially fixed position while the workpiece (2) is moved. Furthermore, the magnet(s) (5) is/are arranged separately from the rollers (4).

Description

CARRIAGE FOR TRAVELLING ON A FERROMAGNETIC WORKPIECE

BACKGROUND OF THE INVENTION

The present invention relates to a carriage for travelling on a ferromagnetic workpiece, said carriage comprising a main body being provided with a plurality of rollers and at least one magnet, wherein the carriage further comprises a tool holder for a tool.

Modern wind turbines have grown considerably in size over the last decades, and at present have towers with a total height of up to 100 m, and even higher towers can be anticipated in the future. Wind turbine towers are typically made up of tubular metal sections, which are connected end to end with bolted joints. To enable the bolted joints, the tubular metal sections are provided with flanges, which are connected to the tubular metal sections by welded joints.

With increasing size the loads on the structure, for example the tower, increase considerably. One reason is that the energy received by the wind turbine increases with the square of the increase in blade length. Furthermore the wind speed will not be constant all over the rotor, and the blades will be subject to more variance of the wind with increased size of the blades, and with increased height of the tower. Local variance of the wind at different positions of the rotor area are due to wind shear, i.e. lower wind speed near the ground than higher up, turbulence, wind shade etc. All these factors increase fatigue loads and extreme loads on the wind turbine. It is hence of major importance that the tower is strong and without flaws.

Welded joints are efficient and cost effective, but must be thoroughly inspected to avoid or reduce the risk of flaws in the joint, which would put the entire construction at risk. Welded joints are difficult to inspect as defects may be embedded within the weld seam, and hence invisible to the human eye.

Carriages of the type mentioned in the introduction are known from various documents. For example WO 00/05027 Al discloses a trolley for a pipeline welding machine. This trolley is guided by a guide band, which is secured to the surface of the pipeline to be welded. The necessity of a guide band considerably increases the labour involved in the inspection and increases the complexity of the system.

Another example can be seen in EP 1 815 938 Al, which relates to a carriage for automatic processes, such as automatic welding. The carriage comprises a right set of wheels, and a left set of wheels, and the carriage comprises a processor controlling the sets of wheels independently of each other, whereby the speed and direction of the carriage can be controlled. This is a very advanced, but expensive system.

EP 0 346 473 Al describes an ultrasonic detector mounted on a carriage comprising wheels and driving means. This is also a complex and expensive system.

US 4,027,528 describes an apparatus for ultrasonic inspection of ferromagnetic materials. The apparatus comprises a telescopically extendable pole member having a carriage attached to the extendable end of the telescope. A mounting frame carries an ultrasonic transducer and a set of wheels consisting at least in part of permanent magnetic material. The magnetic material of the wheels ensures contact between a substantially vertical ferromagnetic surface and the wheels, thereby fixing a distance between the surface and the transducer.

An object of the invention is to provide a carriage of the above kind, which is simple and cost-effective.

DESCRIPTION OF THE INVENTION

To obtain this object the carriage mentioned in the introduction comprises a support adapted for holding the carriage in a substantially fixed position. Hereby a particularly simple, cost efficient and labour-saving carriage is provided. As the carriage is kept in a substantially fixed position, the workpiece may travel in relation to the carriage. By a fixed position should be understood a fixed three dimensional position, e.g. a predetermined position above ground.

The magnet(s) of the main body is/are arranged separately from the rollers. This allows standard wheels and standard magnets to be used, i.e. the requirement for especially manufactured magnetic wheels is avoided. Thereby the manufacturing costs can be considerably reduced while maintaining a good contact between the surface of the ferromagnetic workpiece and the carriage.

The carriage may be designed to have fixed dimensions, which is a particularly simple and hence cost effective embodiment. According to an embodiment, however, the tool holder may be adjustable, whereby the tool can be positioned precisely where it is needed, and the same carriage can be used on surfaces of various dimensions, and the tool can easily be arranged at various positions along the surface of the workpiece.

The tool holder may be adjustable along a direction which is substantially parallel to a part of a surface of the workpiece which is arranged adjacent to the carriage. According to this embodiment, it is possible to position the tool at a position along the surface of the workpiece where operation of the tool is desired, e.g. in order to inspect the surface, without altering the distance between the tool and the surface of the workpiece.

The carriage may be convenient for a variety of different tools, such as welding devices, cameras or the like for surface inspection, etc. According to an embodiment, the tool may be or comprise an ultra sound detector or an ultrasonic detector, whereby ultrasonic inspection of surfaces can be provided. Very efficient ultrasonic detection of e.g. welding seams can thereby be performed. Alternatively, the tool may be or comprise an X-ray detector, whereby X-ray inspection of surfaces can be provided.

According to an embodiment, the main body may define a substantially planar surface, and the main body may comprise at least two rollers having an axis of rotation arranged substantially in parallel with said substantially planar surface. The substantially planar surface is not necessarily a physical surface, but could be a virtual surface, where one or more parts of the main body extend along one or more directions which is/are parallel to the substantially planar surface. The substantially planar surface may be arranged tangentially to an outer surface of the workpiece, or in parallel to a tangential plane of the workpiece. Hereby low friction engagement with the surface to be inspected is achieved, via the rollers.

Although not necessary, it may be beneficial to provide the carriage with a guide arranged to guide the relative movements between carriage and workpiece in at least one direction. Hereby the position in relation to an edge part of a work piece to be inspected can be maintained in a very simple way. For instance, in the case that the workpiece is a substantially cylindrical item, such as a tube or a tower section, the guide may be adapted to abut an end part or a flange of the workpiece during operation. Thereby the guide ensures that the carriage and the workpiece are not moved relative to each other along a longitudinal direction of the workpiece. However, the carriage and the workpiece may still be allowed to perform relative movements along a circumferential direction of the workpiece. Thereby an annular or circumferential welding seam of the workpiece may easily be inspected by means of the tool mounted on the tool holder of the carriage.

The guide may be a simple projecting edge or the like, and the surface thereof may be provided with a friction reducing coating. According to an embodiment, however, the guide may comprise at least one roller, preferably having an axis of rotation allowing it/them to roll on a surface of an end part or a flange of the workpiece as described above. Thereby low friction guiding is provided.

To further improve positioning of the carriage, the carriage may further comprise a guiding magnet arranged at the guide. The guiding magnet helps in ensuring that the guide is kept in contact with the workpiece, preferably a flange or an end part of the workpiece.

At least one of the magnet(s) of the main body may be mounted in such a manner that a gap is defined between the magnet and a surface of the workpiece. According to this embodiment, the magnet(s) is/are not in contact with the workpiece, and thereby no friction occurs between the magnet(s) and the workpiece when the carriage and the workpiece perform relative movements. However, a magnetic attraction force is still present between the magnet(s) and the workpiece, and the carriage is kept in position relative to the workpiece by means of this magnetic attraction force. Thus, according to this embodiment, the only contact between the carriage and the workpiece is between the rollers and a surface of the workpiece, and therefore the friction is minimised.

The magnetic attraction force between a magnet and the workpiece, via the gap, may be at least 50%, such as at least 60%, such as at least 75%, such as at least 90%, of a magnetic attraction force between the same magnet and the same workpiece during contact between the magnet and the workpiece. Thus, the gap should be sufficiently small to ensure that the magnetic attraction force between the magnet and the workpiece is sufficient to keep the rollers of the carriage in firm abutment with an outer surface of the workpiece, and the gap should be sufficiently large to avoid friction between the magnet and the surface of the workpiece. The gap may define a distance between the magnet and a surface of the workpiece which is in the order of a few tenths of a millimetre.

According to an embodiment at least some of the rollers or the magnets may be replaceable. Hereby the rollers and magnets may be renewed when worn, so the cost of maintenance is kept low. Furthermore, the rollers and magnets may be adapted for the specific application of the carriage.

Similarly, the tool holder may be adapted for replacement of the tool, so a worn tool can easily be renewed or a tool can be replaced with another tool for a specific application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following an embodiment of the invention will be described in more detail with a view to the accompanying drawing, in which Fig. 1 is a perspective view of a carriage according to an embodiment of the invention, and

Fig. 2 is a perspective view of the carriage of Fig. 1 seen from a different angle.

DETAILED DESCRIPTION OF THE DRAWINGS

A carriage 1 according to an embodiment of the invention can be seen in Fig. 1 and 2, which are perspective views of the carriage 1 in a working position placed on a surface of a workpiece 2, which here is a tubular tower section. The tower section is arranged in horizontal direction on a bed 12 having means for turning the tower section around the longitudinal axis thereof.

The carriage 1 comprises a main body 3 and a tool holder 6, which is adjustable with respect to the main body 3 to enable adjustable positioning of a tool 7 in relation to the surface of the workpiece 2. The carriage 1 shown is for ultra sonic inspection of welding seams, and hence the tool 7 is a set of ultrasonic detectors for inspection of the welding seam 13, which connects the tower section body with a flange part 14 comprising holes 15 for bolts for interconnection of tower sections on top of each other. The tool holder 6 is slidable along the main body 3, and can be fixed at any desired location along the main body 3, so the ultrasonic detectors can easily be positioned in relation to the area to be inspected, e.g. a welding seam as discussed above. Furthermore, the tool 7 may be arranged in a hinged link to allow for movement towards and away from the surface of the workpiece 2.

The main body 3 of the carriage 1 defines a substantially planar surface 8, which is arranged substantially in parallel to a tangential plane of the surface of the workpiece 2. A surface of the main body 3 forms part of the substantially planar surface 8, thereby defining the Virtual' surface 8 illustrated in the Figures by a dotted line.

The carriage 1 comprises a support 9 to hold the carriage 1 in position, while the tower section is turned, so that a relative movement between the carriage 1 and the surface of the workpiece 2 is achieved. In the carriage 1 shown in Fig. 1 and 2, the support 9 is in the form of a stay, which supports the carriage 1 in a fixed position above the ground. This embodiment is a particularly simple form of support, which is very cost-effective and space-saving kind of support. Alternatively, the carriage 1 could be mounted on a larger frame for support on the ground, and the frame could in turn be provided with wheels for easy manoeuvring thereof. As yet another alternative, the support could be formed as part the bed 12 for the tower section, or adapted for attachment to this bed 12.

The carriage 1 is provided with wheels 4 for low friction engagement with the moving surface of the tower section. The carriage 1 is further provided with magnets 5 to keep the carriage in place on the surface of the tower section, and prevent the carriage from falling off the tower section. The magnets 5 are mounted on the carriage 1 in such a manner that a small gap is formed between each magnet 5 and the surface of the workpiece 2, and the only contact between the carriage 1 and the workpiece 2 is therefore provided by the wheels 4. Thereby friction between the magnets 5 and the workpiece 2 during relative movements of the carriage 1 and the workpiece 2 is avoided. However, the gap should be sufficiently small to allow the magnetic attraction forces between the magnets 5 and the workpiece 2 to keep the carriage 1 in position relative to the workpiece 2.

Some of the wheels 4 are mounted on the carriage 1 in such a manner that they are allowed to roll on the surface of the workpiece 2 which is inspected by means of the tool 7. Other wheels 4 are mounted on the carriage 1 in such a manner that they are allowed to roll on a surface of the flange 14. These wheels 4 function as a guide for the carriage 1 since they ensure that a specified relative position of the carriage 1 and the workpiece 2 is maintained along a substantially axial direction of the tower section. Thereby the tool 7 will remain at a position corresponding to the welding seam 13 as the tower section is rotated.

The carriage 1 is passive, meaning that the carriage 1 is not equipped with any driving means. By 'ferromagnetic' should be understood any material, which will be attracted by a magnet. In the present context tower sections are normally made of a steel alloy, which is ferromagnetic, i.e. the magnets 5 of the carriage 1 will be attracted to the tower section. However the carriage 1 can be used for a workpiece of any other material, which is magnetisable.

The magnets 5 of the carriage 1 may be permanent magnets or electromagnets.

As will be clear to the skilled person the above description presents only some of the possible embodiments and a variety of different alternatives and supplemental details are indeed possible. Although described in relation to wind turbine towers, it will be evident for the skilled person that the carriage could be used for any workpiece, including workpieces having concave or convex surface contours.

Although the above examples are related to ultrasonic testing, it will be evident to the skilled person that other kinds of testing or work on a workpiece can be performed using the carriage.

Claims

1. A carriage (1) adapted for travelling relative to a ferromagnetic workpiece (2), said carriage (1) comprising a main body (3) being provided with a plurality of rollers (4) and at least one magnet (5), the carriage (1) further comprising a tool holder (6) for a tool (7) and a support (9) for holding the carriage (1) in a substantially fixed position while the workpiece (2) is moved, wherein the magnet(s) (5) is are mounted separately from the rollers (4).

2. A carriage (1) according to claim 1, wherein the tool holder (6) is adjustable.

3. A carriage (1) according to claim 2, wherein the tool holder (6) is adjustable along a direction which is substantially parallel to a part of a surface of the workpiece (2) which is arranged adjacent to the carriage (1).

4. A carriage (1) according to any of the preceding claims, wherein the tool (7) is or comprises an ultrasonic detector.

5. A carriage (1) according to any of claims 1-3, wherein the tool (7) is or comprises an X-ray detector.

6. A carriage (1) according to any of the preceding claims, wherein the main body (3) defines a substantially planar surface (8), and wherein the main body (3) comprises at least two rollers (4) having an axis of rotation arranged substantially in parallel with said substantially planar surface (8).

7. A carriage (1) according to any of the preceding claims, wherein the carriage (1) is further provided with a guide arranged to guide the relative movements between carriage (1) and workpiece (2) in at least one direction.

8. A carriage (1) according to claim 7, wherein the guide comprises at least one roller (4).

9. A carriage (1) according to claim 7 or 8, wherein the carriage (1) further comprises a guiding magnet (5) arranged at the guide.

10. A carriage (1) according to any of the preceding claims, wherein at least one of the magnet(s) (5) of the main body (3) is mounted in such a manner that a gap is defined between the magnet (5) and a surface of the workpiece (2).

11. A carriage (1) according to claim 10, wherein the magnetic attraction force between a magnet (5) and the workpiece (2), via the gap, is at least 50% of a magnetic attraction force between the same magnet (5) and the same workpiece (2) during contact between the magnet (5) and the workpiece (2).

12. A carriage (1) according to any of the preceding claims, wherein at least some of the rollers (4) and/or the magnet(s) (5) are replaceable.

13. A carriage (1) according to any of the preceding claims, wherein the tool holder (6) is adapted for replacement of the tool (7).