Abstract:
An apparatus and method for detecting deflection and twisting rotation of an upright structure is provided. At least one laser device is positioned proximate to a first location on the structure. At least one target is positioned proximate to a second location on the structure. The at least one laser device emits parallel laser beams that strike the at least one target at reference locations that indicate a reference position for the upright structure. The laser beams are emitted either periodically or continuously. Any differences between the laser beam receipt locations and the reference locations are calculated to determine any lateral deflection and twisting rotation of the structure relative to the reference position from the first to the second location. The laser beams may be enclosed within a tube.

Description:
[0001]    This application claims benefit from U.S. Provisional Application No. 60/427,623, filed Nov. 19, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates in general to towers and other upright structures, and in particular to an apparatus and method for detecting and measuring tower deflection.  
           [0004]    2. Description of the Related Art  
           [0005]    Towers and other similar free-standing upright structures are used in a variety of applications, for example, as radio and telecommunications antennas or to secure and support various types of payloads. These structures are often subject to forces caused by wind or other phenomena. These forces can cause swaying, bending, torsion or other movement of the tower, which can result in translational and rotational deflection, in particular to the upper portion of the tower relative to the tower&#39;s more stable and securely-fastened bottom portion.  
           [0006]    This deflection can detrimentally affect particular tower applications. For example, if a tower is supporting a payload which comprises a device requiring accurate aiming, such as a directed-energy weapon, small tower deflections may move the energy beam produced by the weapon off a target located a long distance from the tower, requiring correction in response to the tower deflection to maintain the proper aim of the weapon. If the tower deflection could be detected and measured initially, such an occurrence, as well as other similar occurrences, could likely be prevented.  
           [0007]    A need exists, therefore, for an apparatus and method for detecting and measuring real-time deflection of a tower. Further, for those tower applications which involve supporting a payload, a need exists for an apparatus and method which would allow for adjusting components in the payload in response to any measured deflection.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a method of detecting deflection and twisting rotation of an upright structure. At least one laser device is positioned proximate to a first location on the structure. At least one target is positioned proximate to a second location on the structure. The at least one laser device emits at least two parallel laser beams that strike the at least one target at reference locations that indicate a reference position for the upright structure. The laser beams can be emitted either periodically or continuously. The position of the points where the laser beams strike the at least one target are monitored for changes. Any differences between the points where the laser beams strike the at least one target and the reference locations are calculated to determine any lateral deflection and twisting rotation of the structure relative to the reference position from the first to the second location.  
           [0009]    A feature of the present invention is that the upright structure is a tower. Another feature is that the at least one laser device is disposed at or near a base of the structure and the at least one target is disposed at or near a top of the structure. Another feature is that at least one camera is focused at the at least one target to analyze any differences between the laser beam receipt locations and the reference locations with at least one image analyzing computer. Another feature is that the at least one target may have at least one pixel grid that is struck with the laser beams. Another feature is that at least one tube may be mounted between the first location and the second location, and the laser beams may pass through the at least one tube. Another feature is that the at least one laser device may be stationarily mounted relative to the first location and the at least one target may be stationarily mounted relative to the second location. Another feature is that the reference position of the tower is substantially zero deflection and zero twist rotation.  
           [0010]    Another aspect of the present invention provides a method of measuring deflection of an upright structure. A first module is positioned proximate to a first location on the structure, the first module having at least one laser. A second module is positioned proximate to a second location on the structure, the second module having a target. A laser beam is emitted from the laser which strikes a reference location on the target. Any movement of the laser beam on the target relative to the reference location is discerned, and the amount of deflection of the structure based upon any differences in movement is calculated.  
           [0011]    A feature of this aspect of the present invention is that a tube is mounted from the first to the second module. Another feature is that the laser beam emitted from the laser passes through the tube and strikes a reference location on the target. Another feature is that one of the modules is at or near a base of the upright structure and the other of the modules is at or near a top of the upright structure. Another feature is that the first module is disposed at or near the base of the upright structure and the second module is disposed at or near an upper end of the upright structure. Another feature is that any movement of the laser beam on the target is discerned by using a camera focused on the target, the camera being located adjacent the target and offset from the laser beam. Another feature is that the target comprises a pixel grid and any movement of the laser beam on the target is discerned by using a pixel element analyzing computer. Another feature is that the reference location corresponds to zero deflection of the upright structure.  
           [0012]    Another aspect of the present invention provides an apparatus for detecting lateral deflection and twisting rotation of an upright structure. The apparatus includes at least one first module adapted to be mounted adjacent a first location of the structure, at least one second module spaced a distance from the at least one first module and adapted to be mounted adjacent a second location of the structure, a laser emitter disposed at the at least one first module, the emitter capable of emitting at least one laser beam, a target disposed on the at least one second module, the target being capable of receiving the at least one laser beam produced by the emitter, and a detection device that detects any differences between the locations of a plurality of parallel laser beams that strike the target at any time and predetermined reference locations on the target to determine any deflection and rotation of the first location of the upright structure relative to the second location of the upright structure. A feature of this aspect of the present invention is that the emitter is capable of emitting a plurality of parallel laser beams. Another feature is that the upright structure is a tower, and the first and second locations are substantially fixed relative to each other. Another feature is that a tube extends between the at least one first and second modules for enclosing the laser beams. Another feature is that the detection device comprises a camera mounted adjacent to the target such that a line extending from a lens of the camera to the target is at an inclination relative to the laser beams. Another feature is that the target comprises a pixel grid.  
           [0013]    Another aspect of the present invention provides a tower which includes an elongated structure having a base and a top, at least one laser device disposed at a first location on the structure, at least one target disposed at a second location on the structure for receiving a laser beam from the at least one laser device, and a detection device that monitors the at least one target to determine any change in position of where the laser beam strikes the at least one target, thereby indicating deflection of the tower. A feature of this aspect of the present invention is that at least one tube extends from the at least one laser device to the at least one target. Another feature is that the detection device comprises a camera mounted adjacent to the at least one target such that a line extending from a lens of the camera to the at least one target is at an inclination relative to the laser beams. Another feature is that the at least one target includes a pixel grid.  
       
    
    
     Brief Description of the Drawings  
       [0014]    The various aspects of the invention will now be described by way of example only with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a profile view of a tower erected on a support surface and supporting a payload.  
         [0016]    [0016]FIG. 2 is a schematic profile view of a system constructed according to the invention for measuring deflection of the tower of FIG. 1, the system comprising a laser module and a target module.  
         [0017]    [0017]FIG. 3 is a plan view of the base of the tower of FIG. 1 with the laser module of FIG. 2 installed.  
         [0018]    [0018]FIG. 4 is a plan view of the upper portion of the tower of FIG. 1 with the target module of FIG. 4 installed.  
         [0019]    [0019]FIG. 5 is a bottom plan view of a target of the target module of FIG. 2 during operation.  
         [0020]    [0020]FIG. 6 is a schematic view of an electronic collection and data conversion system according to the invention.  
         [0021]    [0021]FIG. 7 is a schematic profile view of an alternative embodiment of the measurement system according to the invention, the embodiment using an optional target module.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIGS. 1 through 7 illustrate two embodiments of an apparatus for measuring translational and rotational deflection of an upper portion of a tower. Deflection is primarily caused by wind exerting a force on the tower, though other forces may also act on tower to cause deflection.  
         [0023]    [0023]FIG. 1 shows a tower  11  constructed on support surface  13 . Tower is preferably formed from a lattice framework  15  of metal members, as shown, though tower  11  may be of other types, such as a polygonal single-pole tower or a tapered cylindrical single-pole tower (not shown). A payload  17  is supported on the upper portion of tower  11 , which may be 300 ft or more above surface  13 . Payload  17  may be of various types, including communications equipment or other electronic equipment.  
         [0024]    To measure deflection and twisting rotation of tower  11 , a preferred embodiment utilizes a two-piece measurement system that is mounted to or near tower  11 . FIG. 2 shows system  19 , comprising one laser module  21  and one target module  23 . In an alternative embodiment, one or more laser modules  21  and/or one more target modules  23  at various locations may be utilized. Laser module  21  is securely mounted on support surface  13  with mounting plate  25  at or near the lower end of tower  11  (FIG. 1). FIG. 3 is a plan view of the lower end of tower  11  showing laser module  21  installed near the central axis  27  of tower  11 . Referring again to FIG. 2, at least one and preferably two lasers  29  are rigidly mounted within module  21  for directing laser beams (not shown) vertically upward near and parallel to line  31 . Laser module  21  is preferably mounted using a precision bracket, allowing the laser beams to be precisely vertical. Lasers  29  are preferably mounted approximately 1.5 in apart.  
         [0025]    Lasers  29  are preferably 30 mW, 632 nm (red) lasers, available from Cemar Electro, Inc. of Champlain, N.Y., though lasers  29  may be any power or produce any light frequency that satisfies the operational requirements of system  19 , as described herein. In the preferred embodiment, the size of each laser beam is approximately 3 mm as it exits laser  29 , widening to approximately 6 mm at 300 ft. At least one cable  33  extends into module  21  to carry electrical power and control data to and from lasers  29 . Preferably, at least one tube  35  is sealingly connected to the upper end of laser module  21  and is preferably coaxial with line  31 , tube  35  preventing airborne contaminants or other objects from interrupting or degrading the beams created by lasers  29 . The beams from lasers  29  travel upward through tube  35  and into target module  23 . Alternatively, lasers  29  may travel upward without using the tube  35 .  
         [0026]    Target module  23  is mounted at an upper portion of tower  11  (FIG. 1), as shown in FIG. 4, preferably directly above laser module  21  (FIG. 3). Target module  23  has a box-shaped enclosure  36  that is sealingly connected to the upper end of at least one tube  35  at joint  37 , which is offset from the center of module  23 . A target surface  39  is formed on the inner surface of upper wall  41  of target module  23 , surface  39  having a color providing high contrast relative to the color of the beams from lasers  29 .  
         [0027]    Referring to FIG. 5, the laser beams strike target  39 , forming visible dots  43 ,  45 . Dots  43 ,  45  have a fixed position, due to lasers  29  being mounted on support surface  13  (FIG. 2), whereas target  39  moves with target module  23  as tower  11  is deflected. By measuring the relative change of the position of dots  43 ,  45  on target  39 , as shown by phantom dots  47  at an actual receipt location, the amount of deflection, in translation or rotation, of tower  11  may be calculated. For example, a change of both in the x or y direction the same amount indicates lateral deflection in the y-direction, but no rotation. A change in x or y direction of one relative to the other indicates twisting rotation of the tower. While two dots  43 ,  45  are shown, the number of dots  43 ,  45  will be equal to the number of lasers  29  (FIG. 2) in use.  
         [0028]    Referring again to FIG. 2, a camera  49 , such as a type available from DVT Corporation of Norcross, Ga., is mounted to a lower portion of module  23  for use as part of a detection device for measuring the change in position of dots  43 ,  45 . Camera  49  is mounted in a position offset from the center of module  23  and at an angle relative to line  31 , camera preferably being approximately 1.5 ft from target  39 . This orients the sightline of camera  49 , indicated by line  45 , for allowing camera  49  to image an area  51 , shown as a broken line in FIG. 5, of target  39  surrounding dots  43 ,  45 . Camera  49  has a lens  53 , which is  8 mm in the preferred embodiment, for focusing light entering camera  49  onto an imaging device  55 , which may be, for example, a charge-coupled device (CCD). Cables  57  carry electrical and data signals to and from camera  49 .  
         [0029]    Imaging device  55  in camera  49  has an array of light-detecting elements (not shown), or pixels, that produce a digital signal when light falls on the pixels. The light from each dot  43 ,  45  reflected from target  39  is detected as an image by a discrete set of these elements, and a software program, which may be run on a computer within camera  49 , is used to analyze the image, determine the centroid of each dot  43 ,  45 , and output the location of the dots in x and y coordinates. Since camera  49  is located off the axis of the laser beams, circular dots  43 ,  45  will appear to be ellipses, though this will not affect the calculations, as the software will determine the centroids to be in the same locations as with circular dots  43 ,  45 . Camera  49  periodically monitors and takes readings of the positions of dots  43 ,  45 , the frequency preferably being within the range of 10-20,000 Hz. The monitoring preferably occurs at a high rate of frequency and preferably in real time. The frequency of monitoring can depend upon, among other factors, the amount of data being monitored and the speed of the computer performing the monitoring.  
         [0030]    In operation, when camera  49  and target  39  move relative to dots  43 ,  45 , which remain stationary as module  23  moves with tower  11 , the light from dots  43 ,  45  falls on pixels at a location on imaging device  55  that is shifted from the previous location. The light is then detected on a different set of pixels, and the software outputs the new location of the centroid of each dot  43 ,  45 , allowing the amount of deflection of tower  11  to be calculated from the change in the positions of dots  43 ,  45  on target  39 .  
         [0031]    [0031]FIG. 6 is a schematic showing one embodiment of an electronic collection and data conversion system using the output of camera  49  to make adjustments based on measured deflection of tower  11 . In this embodiment, camera  49  outputs the x and y coordinate data for dots  43 ,  45  in ASCII characters through cable  57  to an Ethernet-to-serial interface converter  59 . Converter  59  then outputs the data through cable  61  to an SDM-SI04 interface  63 , which can be programmed as needed to create formatted output strings from the received characters. These strings are output through cable  65  to data logger  67 , which records the data and calculates the translation and rotation of tower  11  between data readings. The deflection data is then output through cable  69  to a computer  71  that controls components of payload  17  (FIG. 1) of tower  11 . Thus, the present invention is used to detect real-time deflection of tower  11  to allow for adjusting components in payload  17  in response to the measured deflection. For example, if payload  17  comprises a device requiring accurate aiming, such as a directed-energy weapon (not shown), small deflections of tower  11  may move the energy beam off a target located a long distance from tower  11 . The present invention allows for correction in response to a measured deflection of tower  11  to maintain the proper aim of the weapon. Alternatively, camera  49  may include one or more of the data formatting components described above, and camera  49  may output the deflection data directly to computer  71  through cable  57 .  
         [0032]    An alternative embodiment of the invention is shown in FIG. 7 as measurement system  73 , with target module  23  being replaced by optional target module  75 . Target module  75  is mounted at an upper portion of tower  11 , preferably directly above laser module  21 . Target module  75  has a box- or tube-shaped enclosure  76  that is sealingly connected to the upper end of tube  35  at joint  77 , which is preferably coaxial with the vertical centerline of module  75  and line  31 . At least one pixel grid  79 , similar to imaging device  55  (FIG. 2), is located within module  75  for use as part of a detection device for determining the positions of dots  43 ,  45  (FIG. 5), which are formed on face  81  of grid  79  by beams from lasers  29 . Grid  79  is mounted in module  75  such that face  81  is approximately normal to and centered on line  31 . Face  81  comprises a plurality of discrete pixel elements (not shown) that produce a digital signal when light from lasers  29  strike the elements, allowing the positions of dots  43 ,  45  on face  81  to be detected directly. Cables  83  carry electrical power and data signals to and from grid  79 . Grid  79  will typically be connected to computer  71  through a plurality of data analysis and formatting components, as shown for camera  49  in FIG. 6. While shown as having one grid  79  for detecting all of dots  43 ,  45 , module  75  may have two or more grids  79 , each for detecting one or more dots  43 ,  45 .  
         [0033]    In operation, when pixel grid  79  moves relative to dots  43 ,  45 , which remain stationary as module  75  moves with tower  11 , the light from dots  43 ,  45  falls on pixels at an actual receipt location on grip  79  that is shifted from the previous location. The light is then detected on a different set of pixels, and pixel grid  79  outputs the new set of pixels detecting each dot  43 ,  45 . This allows translational and rotational deflection of tower  11  to be calculated from the change in the positions of dots  43 ,  45  on face  81 .  
         [0034]    The present invention has several advantages. The invention provides a simple and low-cost apparatus and method for detecting and measuring deflection of a tower or similar object, and the precision of the system is limited only by the rate of data capture and the resolution of the camera or pixel grid of the target module. The system may be easily attached to or removed from an existing structure or may be incorporated in new construction.  
         [0035]    While the invention has been described herein with respect to a preferred embodiment, it should be understood by those that are skilled in the art that it is not so limited. The invention is susceptible of various modifications and changes without departing from the scope of the claims. For example, if twisting rotation is not a measurement that is needed, a single laser beam would be sufficient. Also, the lasers could be mounted at the upper end of the tower and the target at the base.