Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application No. 61/178,682 filed on May 15, 2009; the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a mast assembly and a method of erecting such an assembly. 
     SUMMARY OF THE INVENTION 
     A mast assembly is used where a device needs to be elevated in order to perform effectively. Such apparatus may for example be a light structure, a sign, a telecommunications antenna or a wind power turbine. The elevation obtained from the mast will vary and for high value equipment or significant elevations, a customized assembly process can be justified. However, there are many applications where a relatively modest elevation is required and customized assembly of the mast and the equipment cannot be economically justified. 
     Moreover, in some situations it is necessary to provide for ongoing maintenance and repair of the equipment supported by the mast which makes dismounting of the mast desirable. 
     A typical application requiring a simple but robust method of erecting a mast is in the installation of relatively small wind powered generators. These generators may be installed in a location to supply power to meet the needs of an individual residence and therefore their erection does not justify the expense of custom installation. Nevertheless, the mast may typically range from 16 to 30 meters high and the mass of the turbine mounted on the upper end of the mast makes raising of the mast difficult. It is also desirable to be able to lower the mast in the event of inclement weather to avoid damage to the turbine, or other equipment mounted on the mast. 
     One proposal to facilitate the erection of the mast is to pivot the mast to a base and utilize hydraulic cylinders between the base and the mast to move the mast from a horizontal to a vertical position. The mast may then be bolted to the base to maintain it in a stable position. However, with this arrangement the large moment arm presented by the mast and turbine assembly and the distance through which the hydraulic pistons must act requires the use of a pair of multi stage telescopic hydraulic actuators. These actuators are relatively expensive and add significantly to the cost of the installation. 
     It is therefore an object of the present invention to provide a method and apparatus for erecting a mast in which the above disadvantages are obviated or mitigated. 
     In general terms, the present invention provides a mast assembly having a base and a mast pivotally connected to the base for movement between a horizontal and upright position. A linear actuator is connected between the base and the mast and is extensible to move the mast about the pivot. A strut is selectively engagable between the mast and the base to inhibit pivotal movement toward the horizontal position. The linear actuator can be selectively positioned in one of a plurality of abutments on one of the base and the mast so that when the strut is positioned to support the mast, the actuator can be moved between the plurality of abutments. In this way, a single stage hydraulic cylinder may be used with a stroke less than that needed to accomplish movement from horizontal to vertical position. The provision of the strut allows repositioning of the cylinder during erection so that the required range of movement can be achieved without resorting to multistage cylinders. 
     Preferably, the plurality of abutments are formed on the base in a earn track. The strut similarly moves along a cam track having a pair of notches so that after initial extension of the cylinder, the strut is engaged between the mast and the first of the notches along the motor to be retracted. Further extension moves the strut into the second notch allowing repositioning of the actuator for further pivotal movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will now be described by way of an example only with reference to the accompanying drawings in which: 
         FIG. 1  is a side elevation of a wind turbine. 
         FIG. 2  is a view on an enlarged scale of a portion of the turbine shown in  FIG. 1 . 
         FIG. 3  is a front section on the line of  FIG. 2 . 
         FIG. 4  is a view similar to  FIG. 2  showing the mast of  FIG. 1  in an intermediate position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring therefore to  FIG. 1 , a wind turbine generally indicated  10  includes a base  12 , a mast  14 , and a generator assembly  16 . The generator assembly  16  is mounted as a self contained assembly on a flange  18  at the upper end of mast  14  and has a blades  20  that rotate about a horizontal axis to generate power in a conventional manner. 
     The mast  14  is formed from a number of sections, namely, lower section  22 , middle section  24  and upper section  26 , that are bolted to one another at flanges  28 ,  30  respectively to form a unitary construction. Alternatively the tower can also be formed by different types of construction such as a slip fit design where there are no bolts or flanges. This alternate design is boltless and the sections secure themselves via compression between the sections to hold them together. The overall length of the mast may be 16 to 30 metres in typical applications to support a generator  16  having blades  20  of an overall length of 2 metres to 8 meters. It will be appreciated that the dimensions, including the overall height of the mast may vary to suit particular applications and the loads that may be imposed on the mast. 
     The lower section  22  of the mast  14  is provided with a flange  32  that abuts against a flange  34  provided on the upper side of the base  12 . The flanges  32 ,  34  are connected by a hinge  36  formed between ears  38 ,  40  extending from the flanges  32 ,  34  respectively. A pin  42  passes between the ears  38 ,  40  to define a pivot axis between the mast  14  and base  12  that is offset to one side of the mast  14 . The mast  14  is therefore able to pivot from a generally horizontal position, as shown in dashed outline in  FIG. 2 , to an upright, generally vertical position as shown in solid lines in  FIG. 2 . 
     A linear actuator  44  which is conveniently in the form of a double acting hydraulic motor, extends between the base  12  and the mast  14  to effect pivotal movement about the pin  42 . The actuator  44  has a piston rod  46  that is secured to a clevis  48  defined between a pair of plates  50 ,  52  welded to the lower section  22  of mast  14 . A bolt  54  passes between the plates  50 ,  52  and through boss  55  on the rod  46  to pivotally connect the rod to the mast. The rod  46  slides within a cylinder  56  that is located between a pair of walls  58 ,  60  that form part of the base  12 . 
     Each of the walls  58 ,  60  has a cam track indicated at  62  formed in it that controls relative movement between the cylinder  56  and base  12 . A connector in the form of a bolt  64  is connected to the cylinder and extends to either side into the cam track  62 . The cam track  62  has a lower closed end  65  and pair of notches  66 ,  68  respectively formed in the lower edge of the track. The end  65  and notches  66 ,  68  form apertures to receive the bolt  64  at different pivotal positions of the mast on the base. The notch  66  is located at the mid point of the cam track  62  and is dimensioned to be able to receive the bolt  64  and maintain it in a stable position. The notch  68  is located at the upper end of the cam track  62  and similarly is dimensioned to receive the bolt  64  in a stable location. The end  65  and notches  66 ,  68  provide three abutments for transferring load from the actuator  44  to the base  12 . 
     A strut  70  is connected to the mast  14  through a clevis  72  located immediately above the clevis  48 . The strut  70  is connected to the clevis  72  by a pin  74  and the lower end of the strut  70  has a pair of cylindrical knobs  76  that project to opposite sides of the strut  70 . The strut  70  is formed from a tube and has sufficient buckling strength to be able to support the load imposed by the mast  14  when in a horizontal or inclined position. 
     The outer vertical edge of the walls  58 ,  60  is formed with a pair of notches  78 ,  80  that are dimensioned to received the knobs  76  and hold them in a stable position. The walls  58 ,  60  are reinforced by reinforcing strips  82  so as to resist buckling when loads are imposed by the strut on the walls. 
     In order to erect the mast  14 , it is initially connected by the pin  42  to the base  12  and extends in a horizontal direction as shown in  FIG. 2 . In that position, the generator assembly  16  may be attached to the mast and the necessary commissioning and servicing performed prior to the mast  14  being erected. 
     When the mast is ready to be erected, the actuator  44  is connected to the clevis  48  by the bolt  54  and the lower end of the cylinder  56  connected to the cam track  62  by the bolt  64 . Initially, the actuator  44  is fully retracted and the bolt  64  abuts against the closed end  65  of the track  62 . The strut  70  is also connected to the clevis  72  through the pin  74  and rests against the base  12 . The actuator  44  is connected to a hydraulic power pack to supply hydraulic fluid to the cylinder  56  and extend the rod  46  from the cylinder. Preferably, the power pack is located in the base  12  and includes a reservoir and an electrically driven pump to supply the pressurised fluid. The cylinder  56  and rod  46  are dimensioned to have sufficient diameter so that the vertical loads imposed by the mast can be overcome. 
     As shown in  FIG. 4 , as the actuator  44  extends, the mast  14  pivots about the pin  42  and moves from a horizontal towards an upright position. During this movement, the bolt  54  abuts the end  65  of the cam track  62  and the lower end of the strut  70  moves along the outer edge of the plates  50 ,  52  toward the notch  66 . 
     As the actuator  44  reaches the limit of its stroke, the knobs  76  drop into the notch  78 . The hydraulic supply to the actuator  44  can then be reversed to retract the rod into the cylinder. The strut  70  supports the mast in a stable inclined position and retraction of the rod  46  causes the bolt  54  to move along the cam track  62  towards the notch  66 . As the actuator  44  reaches the minimum length, the bolt  64  drops into the notch  66  to provide a further stable connection between the base  12  and the mast  14 . Thereafter, the actuator  44  may again be extended to continue pivotal movement of the mast  14  relative to the base  12  and to pull the strut  70  along the outer surface toward the notch  80 . Extension of the actuator  44  continues until the knobs  76  are aligned with the notches  80  at which time the actuator  44  can again be retracted to move the bolt  64  into the notch  68 . Continued extension of the actuator  44  completes the pivotal movement of the mast whilst carrying the strut  70  out of the notch  80 . In this manner, the actuator  44  can be stepped along the cam track  62  to supply successive lifting forces. The strut  70  is operable to maintain the mast in a stable position whilst the actuator  44  is being repositioned. 
     Once in an upright position, the flanges  32 ,  34  are bolted to one another to provide a rigid connection and the actuator  44  may be removed or it can stay attached to the tower for local storage. 
     It will of course be appreciated that if it becomes necessary to lower the mast for servicing or changing of components, the reverse operation may be completed to provide a controlled lowering through the alternate use of the strut and the actuator. 
     It will also be appreciated that the cam track  62  can be located on the mast with a fixed pivot connection to the base and that the number of notches along the cam track may be increased or decreased to suit a particular application. The actuator  44  may be a mechanical actuator, such as a re-circulating ball, screw jack, if preferred. 
     It is also possible to provide the abutments between the actuator and the base as individual holes, rather than notches connected by the cam track  62 . With this arrangement, which enhances the stability of the walls  58 ,  60 , the bolt  64  is formed as a removable pin that is inserted through the holes and a bearing on the actuator to connect the actuator and base. When the mast is supported by the strut, the pin is withdrawn and the actuator reposition so as to be aligned with the adjacent hole. Similarly, the connection between the strut and base can be formed as individual holes with a removable pin if preferred. 
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. Although the mast assembly has been described in the context of supporting a wind turbine, it will be appreciated that other equipment may be supported in the mast, such as lights, antennas, and signs. The entire disclosures of all references recited above are incorporated herein by reference.

Technology Category: f