Abstract:
A safety latch telescoping mast system for a portable light tower having a towable trailer having a frame and an engine driven electrical generator and a light assembly for attachment to the uppermost end of a telescoping mast member, which includes a pivotable spring loaded safety latch assembly positioned to remain in a first, cocked, position wherein an idler roller is in rotational engagement with a hoisting cable and the latch is outside the opening in the stationary mast member when the first hoisting cable is under tension, which trips to a second, position wherein the latch passes through the opening in the stationary mast member and engages into a slot in the first telescoping mast member when the tension on the first hoisting cable is relieved.

Description:
FIELD OF INVENTION 
     This invention generally relates to portable light towers used at construction sites having a telescoping light tower mast and a safety latch system to prevent collapse of an elevated light tower mast. 
     BACKGROUND OF INVENTION 
     Much outdoor construction activity occurs at night, particularly when it relates to highway improvements, since traffic counts are greatly reduced at night and inconvenience to the general public is minimized. A common way of illuminating a worksite is with a trailerable portable light tower. These light towers generally are assembled on small towable trailers which include an engine driven generator set operably connected to a light bar assembly which is mounted at the top of a mast which can be raised and lowered as needed. Oftentimes, the mast can be raised to an elevation of 20 to 30 feet above the trailer. 
     The mast must be capable of being raised and lowered. A portable trailer having a light tower mast that extends 30 feet into the air cannot be easily towed around without lowering the mast. The masts are generally not made of unitary construction since that would entail lowering the mast by pivoting it down where it would extend 30 feet back out behind the trailer. Instead, they are normally made of four or five telescoping pieces which can be lowered into a convenient stationary mast base so that the top of the trailer when the mast is fully lowered is no more than about 8 feet above ground. Such a trailer is then easily portable and can be moved about conveniently, and can even be stored or repaired indoors. 
     There are a number of ways of raising and lowering a mast, which include hydraulic systems, which are expensive and require additional equipment, namely a hydraulic pump and hydraulic plumbing and the supply of hydraulic fluid so as to extend the mast up and later retract it. The most common method of extending and retracting the mast is a wire cable and winch assembly. 
     A problem, which occurs more frequently than is desired, is that the cables used to extend and retract the mast will occasionally snap or part. When this occurs, all of the telescoping pieces come crashing down, one into the other, and if the operator happens to be standing underneath the mast at the time it comes crashing down, the operator can be seriously injured or even killed as the mast itself will typically weight 200 to 300 pounds. When they crash down, that light bar can land with a force in excess of 700 pounds which can be fatal to an unfortunate operator who happens to be standing underneath the mast at the time it comes crashing down. 
     Various attempts at providing some kind of safety catch for elevated light tower masts have been attempted in the past. In the case where a hydraulic system is used to raise and lower the mast, any failure of the hydraulic system, for example a burst hose, will simply result in the mast slowly dropping, and there is adequate time for anybody under the light tower mast to clear the area before the mast and its associated light tower is fully down. In the case of cable-powered elevation systems, one common practice has been to use some sort of a safety clevis pin to lock one or more pieces of the mast in place. However, this has not been a satisfactory arrangement because clevis pins are commonly misplaced and/or lost, or because the operator fails to install the clevis pin properly, or because the mast is raised to some intermediate position where the holes through which the clevis pin is to be inserted do not properly line up. 
     What is needed is an automatic latching system which by default is always operable to catch the mast and hold it in position in the event that the hoisting cables fail. 
     SUMMARY OF THE INVENTION 
     The purpose of the Summary is to enable the public, and especially the scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection, the nature and essence of the technical disclosure of the application. The Summary is neither intended to define the inventive concept(s) of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the inventive concept(s) in any way. 
     Still, other features and advantages of the presently disclosed and claimed inventive concept(s) will become readily apparent to those skilled in this art from the following detailed description describing preferred embodiments of the inventive concept(s), simply by way of illustration of the best mode contemplated by carrying out the inventive concept(s). As will be realized, the inventive concept(s) is capable of modification in various obvious respects all without departing from the inventive concept(s). Accordingly, the drawings and description of the preferred embodiments are to be regarded as illustrative in nature, and not as restrictive in nature. 
     A trailerable light tower is formed of a trailer having a motor generator within housing and trailer tongue and stabilizing jacks. A mast assembly is provided and affixed to trailer tongue. The mast assembly is formed of one stationary member which is firmly attached to the trailer and at least a first telescoping member, and may include multiple additional telescoping members. Atop the uppermost telescoping member is operably attached a light bar assembly. 
     An electric hoisting cable winch is provided which may be affixed to the stationary member or some other convenient anchor point. A first hoisting cable is attached to the hoisting cable winch at one end then wound over the top of a first hoisting pulley attached to the stationary member and down in between the space between the side walls of the stationary member and the first telescoping member and attached to the first telescoping member generally near the base of the first telescoping member. 
     In a like manner, in the event there is a second telescoping member a second hoisting cable is also attached to the stationary member and wound over the top of a second hoisting pulley on the stationary mast member or the first telescoping member, and down to the bottom and attached generally to the base area of the second telescoping member. 
     In a like manner, in the event there is a third telescoping member, a third hoisting cable is fixedly attached to the top of the first telescoping member and wound over the top of a third hoisting pulley attached to the second telescoping member and attached to the base of the third telescoping member. This same hoisting cable arrangement can be repeated with additional telescoping members, if the mast is so provided with them. The top of the first telescoping member can be thought of as a stationary anchor point relative to second telescoping member which is the driving force for the hoisting cable of the third telescoping member as the first telescoping mast member is driven upwards by the first hoisting cable and winch. 
     A safety latch assembly is also provided and located where it is in rotational and frictional engagement with the first hoisting cable. 
     In the event there are multiple telescoping members then the first hoisting cable will inherently carry a strain for the entire weight of the mast assembly, and the strain can easily exceed 1,000 pounds per square inch, especially if the mast is being elevated in a windy location or when the portable light trailer is not on perfectly level ground. As a result, the first hoisting cable is by far the most likely of the cables to fail. If the first hoisting cable fails, then the first telescoping member will come crashing down into the stationary member and subsequently, all of the remaining telescoping members will also come crashing down with significant and potentially lethal force. 
     Accordingly, a spring loaded safety latch assembly is provided. The safety latch assembly is formed of a mounting bracket with a spring post and a spring which interconnect to a pressure plate which is affixed between a first latch bracket and a second latch bracket. Also attached to the pressure plate is a latch which is formed with an integral latch hook. The latch assembly formed of the first latch plate and the second latch plate and the pressure plate is pivotally mounted to the mounting bracket by means of a pin which forms a pivot point. An idler pulley, also rotationally mounted between the two latch plates is provided with a helical screw thread which enables the first hoisting cable to travel laterally on the idler pulley to minimize side loads on the first hoisting cable as the cable is wound onto and off of the winch. 
     The safety latch assembly is mounted in a position wherein as long as there is tension on the first hoisting cable, the idler pulley and latch plates force the spring into a fully compressed position. In the event that the first hoisting cable snaps and breaks, the tension force of the first hoisting cable, which is holding the idler pulley in position, is released and the spring forces the idler pulley down onto an appropriate surface, and concurrently pivoting the latch in through a slot through the side wall of the stationary member and into one of a plurality of slots that have been pre-formed in the first telescoping member thereby catching the first telescoping member before it falls to the bottom of the stationary mast member. 
     The spring provides enough compressive force such that it will expand out once idler pulley is released by reason of a broken first hoisting cable to engage the latch valley of the latch in one of the slots in the first telescoping member within one-tenth of one second and the mast assembly will only drop a couple of inches before all of the telescoping members come to rest in the event that first hoisting cable were to fail. This is assured by the cabling arrangement which slaves the second through the fourth telescoping members to the stationary member and the position of the first telescoping member. 
     It can be said that the positioning of the safety latch for engagement of the idler pulley with the first hoisting cable holds the safety latch assembly in the cocked position. It has been found in practice that oftentimes the operator when he lowers the mast to its transport position will relieve the tension on the first hoisting cable, in which case the released cable tension allows the latch to engage in a slot in the first telescoping member. However, as soon as the operator engages the winch to elevate the mast, the cable tension is restored and the safety latch assembly will be repositioned into its cocked position and clear of the slots in the first telescoping member. 
     In this manner, safety latching mechanism is provided for the mast which is automatic in operation, and requires no operator intervention, and does not require any pins or manual latches to be engaged. It will work at all heights, and it does not require that the mast be elevated to certain selected heights where holes for a safety pin or clevis pin are aligned to allow insertion of the safety or clevis pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified side view of a portable light tower having an automatic safety latch assembly for the mast tower. 
         FIG. 2  is a perspective representational view of the first telescoping member. 
         FIG. 3  is a cut-away representation of the stationary mast member and first and second telescoping members in a retracted position. 
         FIG. 4  is a cut-away representation of the stationary mast member and first and second telescoping members in a partially elevated position. 
         FIG. 5  is an exploded view of the safety latch assembly. 
         FIG. 6  is a perspective view of the safety latch assembly. 
         FIG. 7  is a sectional view of the safety latch mechanism taken along the plane A-A of  FIG. 6 . 
         FIG. 8  is a representational sectional side view of the safety latch assembly in the cocked position. 
         FIG. 9  is a representational sectional side view of the safety latch assembly in the tripped position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the presently disclosed inventive concept(s) is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the inventive concept(s) to the specific form disclosed, but, on the contrary, the presently disclosed and claimed inventive concept(s) is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the inventive concept(s) as defined in the claims. 
       FIG. 1  shows a simplified side view of the portable light tower with the safety latch mechanism installed. Towable light tower  10  is formed of trailer  12  having an engine driven generator set (not shown) within housing  14  and trailer tongue  16  or otherwise affixed to the trailer, and stabilizing jacks  18 . Mast assembly  20  is provided and affixed to trailer tongue  16 . The mast assembly  20  is formed of stationary member  22  which is firmly attached to trailer tongue  16  and first telescoping assembly  24 , second telescoping assembly  26 , third telescoping assembly  28 , and fourth telescoping assembly  30 . Atop the fourth telescoping assembly  30  is attached a light bar assembly  32 . Not shown is the appropriate electrical wiring and associated cabling which play no part in the present invention. 
     An electric hoisting cable winch  34  is provided and affixed to the stationary member  22  which is attached to a first hoisting cable  36 . 
     Now referring to  FIGS. 1, 3 and 4 , the hoisting cabling system is shown and described. There is a first hoisting cable  36 , which is attached to hoisting cable winch  34  at one end then wound over the top of first hoisting pulley  80  and down in between the space between the side walls of stationary member  22  and first telescoping member  24  and attached to first telescoping member  24  generally near the base of first telescoping member  24 . 
     In a like manner, as is shown in  FIG. 3 , second hoisting cable  38  is also attached stationary member  22  and wound over the top of second hoisting pulley  82  and down to the bottom and attached generally to the base area of second telescoping member  26 . 
     In a like manner, as shown in  FIG. 1 , the third hoisting cable  40  is fixedly attached to the top of first telescoping member  24  and wound over the top of third hoisting pulley  84  and attached to the base of third telescoping member  28  and fourth hoisting cable  42  is attached to second telescoping member  26  and wound over the top of fourth hoisting pulley  86  and attached to the base of fourth telescoping member  30 . For clarity,  FIGS. 3 and 4  only show the stationary mast member  22  and first and second telescoping members  24  and  26 . But it should be apparent to those skilled in the art that exactly the same configuration is used for the third and fourth telescoping members  28  and  30  using different hoisting cable anchor points. Hoisting cable winch  34  is provided rigidly affixed to stationary member  22 . In the preferred embodiment, stationary member  22  and all of the telescoping members,  24  through  30 , are approximately five feet in length so that when the mast is fully extended, the light bar is positioned approximately 25 feet above the tongue of the portable trailer. 
     Safety latch assembly  50  is also provided and rotational and frictional engagement with first hoisting cable  36 . In the preferred embodiment, hoisting cable winch  34  is electrically operable from a switch location where the operator must stand clear of the mast when it is being elevated or lowered. Third and fourth telescoping members  28  and  30  are also pulled out as a result of the first telescoping member  24  being extracted out of the stationary member  22 . It can be said that the cabling arrangement is slaved to the first hoisting cable  36  because each of the subsequent hoisting cables are attached to an earlier telescoping member which is being forced up and out of its nested position to the elevated position. 
     Each of the four separate hoisting cables,  36  through  42 , is lifting a progressively lighter load. The first hoisting cable  36  carries a strain for the entire weight of the mast assembly, and the strain can easily exceed 1,000 pounds per square inch, especially if the mast is being elevated in a windy location or when the linked portable light trailer is not on perfectly level ground. As a result, the first hoisting cable  36  is by far the most likely of the cables to fail. In fact, in practice it has been found that first hoisting cable  36  can easily fail in as little as 150 to 200 cycles of elevating the mast up and lowering it down. If the first hoisting cable  36  fails, then the first telescoping member comes crashing down into the stationary member and subsequently, all of the remaining telescoping members come crashing down with significant and potentially lethal force. 
     Accordingly, safety latch assembly  50  is provided. Referring now to  FIGS. 5, 6 and 7 , there is shown and described the safety latch assembly  50 . Mounting bracket  52  is provided with spring post  54  and spring  56  which interconnect to pressure plate  62  which is affixed between first latch bracket  58  and second latch bracket  60 . Also attached to pressure plate  62  is latch  64  which is formed with integral latch hook  66 . The latch assembly formed of first latch plate  58  and second latch plate  60  and pressure plate  62  is pivotally mounted to mounting bracket  52  by means of pin  78  which forms a pivot point. Idler pulley  70 , which is attached to safety latch assembly  50  by means of shaft, is provided with a helical screw thread  71  which enables the first hoisting cable  36  to travel laterally on idler pulley  70  to minimize side loads on the first hoisting cable  36  as the cable is wound onto and off of winch  34 . 
     The safety latch assembly  50  is mounted in a position wherein as long as there is tension on first hoisting cable  36 , the idler pulley  70  forces spring  56  into a fully compressed position. This is shown in  FIG. 8 . In the event that first hoisting cable  36  snaps and breaks, the tension force which is holding idler pulley  70  in position is released and spring  56  forces the idler pulley  70  down onto an appropriate surface, and concurrently, latch  64  is pivoted in through a slot through the side wall of stationary member  22  and into one of the plurality of slots  44  that have been formed in the first telescoping member  24 , as shown in  FIGS. 2 and 9 . 
     Spring  56  provides enough compressive force such that it will expand out once idler pulley  70  is released by reason of a broken first hoisting cable  36  to engage latch valley  66  of latch  64  in one of the slots  44  within one-tenth of one second and the mast assembly  20  will only drop a couple of inches before all of the telescoping members come to rest in the event that first hoisting cable  36  were to fail. This is assured by the cabling arrangement which slaves the second through the fourth telescoping members to the stationary member and the position of the first telescoping member. 
     The arrangement of safety latch  50  and its engagement with first hoisting cable  36  holds the safety latch assembly in the cocked position. It has been found in practice that oftentimes the operator when he lowers the mast to its transport position will relieve the tension on first hoisting cable  36 , in which case, latch  64  will engage in a slot  44  in the first telescoping member  24 . However, as soon as the operator engages the winch to elevate the mast  20 , the tension is restored and the safety latch assembly  50  will be repositioned into its cocked position and clear of slots  44  and first telescoping member  24 . 
     In this manner, safety latching mechanism is provided for the mast which is automatic in operation, it requires no operator intervention, and does not require any pins or manual latches to be engaged. It will work at all heights, and it does not require that the mast be elevated to certain selected heights where holes for a safety pin or clevis pin are aligned to allow insertion of the safety or clevis pin. 
     While certain preferred embodiments are shown in the figures and described in this disclosure, it is to be distinctly understood that the presently disclosed inventive concept(s) is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the disclosure as defined by the following claims.