Patent Publication Number: US-9415985-B1

Title: Method for lifting with mast collision control apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to lifts with lifting masts that move in lifting and lowering directions and, more particularly, to lifting mast collision control systems for ensuring the safe movement of a lifting mast in lifting and lowering directions for safeguarding against damage to cargo to be lifted and lowered by the lifting mast. 
     BACKGROUND OF THE INVENTION 
     Lift devices are commonly used to lift workers and equipment during construction, painting, maintenance, assembly, installation, and manufacturing operations. Of particular significance are lifts incorporating lifting masts the move in lifting and lowering directions for lifting and lowering loads supported by the lifting mast, such as on a platform or other load-supporting structure or implement managed by the lifting mast. When a lift incorporating such a lifting mast is being operated near overhead obstructions, such as overhead fixtures, equipment, ducts, rafters, ceilings, or the like, operator error or miscalculation can result in the top of the lifting mast encountering an overhead obstruction, which can cause damage to the lift and/or to the load borne by the lifting mast. What is therefore needed is a lifting mast collision control system that controls the operation of the lifting mast for ensuring the safe operation of the lifting mast against collision of the lifting mast with an overhead obstruction. 
     SUMMARY OF THE INVENTION 
     According to the principle of the invention a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A head is positioned above and over the top of the lifting mast, and is mounted to the lifting mast for displacement between a neutral position away from the top of the lifting mast and a safe position toward the top of the lifting mast in response to the head contact encountering an object above the top of the lifting mast and the head. The drive assembly is enabled for moving of the lifting mast in the lifting and lowering directions in the neutral position of the head, the drive assembly is enabled for moving the lifting mast in the lowering direction in the safe position of the head, and the drive assembly is disabled for moving the lifting mast in the lifting direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the lifting mast. The head is mounted to the lifting mast for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the lifting mast. The head covers the top of the lifting mast so as to shield the top of the lifting mast from directly contact encountering an object above the top of the lifting mast and the head. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A head is positioned above and over the top of the lifting mast, and is mounted to the lifting mast for displacement between a neutral position away from the top of the lifting mast and a safe position toward the top of the lifting mast in response to the head contact encountering an object above the top of the lifting mast and the head. A switch is operatively coupled to the drive assembly. The switch interacts between the head and the lifting mast enabling the drive assembly for moving the lifting mast in the lifting and lowering directions in the neutral position of the head, disabling the drive assembly for moving the lifting mast in the lifting direction in the safe position of the head, and enabling the drive assembly for moving the lifting mast in the lowering direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the lifting mast. The head is mounted to the lifting mast for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the lifting mast. The head covers the top of the lifting mast so as to shield the top of the lifting mast from directly contact encountering an object above the top of the lifting mast and the head. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A base is removably coupled to the top of the lifting mast. A head is positioned above and over the base and the top of the lifting mast, and is mounted to the base for displacement between a neutral position away from the base and the top of the lifting mast and a safe position toward the base and the top of the lifting mast in response to the head contact encountering an object above the base and the top of the lifting mast. The drive assembly is enabled for moving of the lifting mast in the lifting and lowering directions in the neutral position of the head, the drive assembly is enabled for moving the lifting mast in the lowering direction in the safe position of the head, and the drive assembly is disabled for moving the lifting mast in the lifting direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the base. The head is mounted to the base for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the base. The head covers the base and the top of the lifting mast so as to shield the base and the top of the lifting mast from directly contact encountering an object above the base and the top of the lifting mast. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A base is removably coupled to the top of the lifting mast. A head is positioned above and over the base and the top of the lifting mast, and is mounted to the base for displacement between a neutral position away from the base and the top of the lifting mast and a safe position toward the base and the top of the lifting mast in response to the head contact encountering an object above the base and the top of the lifting mast. A switch is operatively coupled to the drive assembly. The switch interacts between the head and the base enabling the drive assembly for moving the lifting mast in the lifting and lowering directions in the neutral position of the head, disabling the drive assembly for moving the lifting mast in the lifting direction in the safe position of the head, and enabling the drive assembly for moving the lifting mast in the lowering direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the base. The head is mounted to the base for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the base. The head covers the base and the top of the lifting mast so as to shield the base and the top of the lifting mast from directly contact encountering an object above the base and the top of the lifting mast. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A head is positioned above and over the top of the lifting mast, and is mounted to the lifting mast for displacement between a neutral position away from the top of the lifting mast and a safe position toward the top of the lifting mast in response to the head contact encountering an object above the top of the lifting mast and the head. A switch is operatively coupled to the drive assembly. An abutment is coupled between the head and the switch and is coupled to interact with the switch in response to movement of the head between the neutral and safe positions causing the switch to enable the drive assembly for moving the lifting mast in the lifting and lowering directions in the neutral position of the head, causing the switch to disable the drive assembly for moving the lifting mast in the lifting direction in the safe position of the head, and causing the switch to enable the drive assembly for moving the lifting mast in the lowering direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the lifting mast. The head is mounted to the lifting mast for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the lifting mast. The head covers the top of the lifting mast so as to shield the top of the lifting mast from directly contact encountering an object above the top of the lifting mast and the head. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A base is removably coupled to the top of the lifting mast. A head is positioned above and over the base and the top of the lifting mast, and is mounted to the base for displacement between a neutral position away from the base and the top of the lifting mast and a safe position toward the base and the top of the lifting mast in response to the head contact encountering an object above the base and the top of the lifting mast. A switch is operatively coupled to the drive assembly. An abutment is coupled between, one the one hand, the head and the base, and, on the other hand, the switch, and the abutment is coupled to interact with the switch in response to movement of the head between the neutral and safe positions causing the switch to enable the drive assembly for moving the lifting mast in the lifting and lowering directions in the neutral position of the head, causing the switch to disable the drive assembly for moving the lifting mast in the lifting direction in the safe position of the head, and causing the switch to enable the drive assembly for moving the lifting mast in the lowering direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the base. The head is mounted to the base for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the base. The head covers the base and the top of the lifting mast so as to shield the base and the top of the lifting mast from directly contact encountering an object above the base and the top of the lifting mast. 
     According to the principle of the invention, a lift device includes a lifting mast having a top, and a drive assembly for moving the lifting mast in lifting and lowering directions. A base is removably coupled to the top of the lifting mast. A head is positioned above and over the base and the top of the lifting mast, and is mounted to the base for displacement between a neutral position away from the base and the top of the lifting mast and a safe position toward the base and the top of the lifting mast in response to the head contact encountering an object above the base and the top of the lifting mast. A switch is carried by the base and is operatively coupled to the drive assembly. An abutment is coupled to the head, and is positioned to interact with the switch in response to movement of the head between the neutral and safe positions causing the switch to enable the drive assembly for moving the lifting mast in the lifting and lowering directions in the neutral position of the head, causing the switch to disable the drive assembly for moving the lifting mast in the lifting direction in the safe position of the head, and causing the switch to enable the drive assembly for moving the lifting mast in the lowering direction in the safe position of the head. A bias is applied to the head tending to bias the head from the safe position to the neutral position. The bias is supplied by at least one spring interacting between the head and the base. The head is mounted to the base for displacement between the neutral and safe positions with a linkage assembly interacting between, or otherwise coupled between, the head and the base. The head covers the base and the top of the lifting mast so as to shield the base and the top of the lifting mast from directly contact encountering an object above the base and the top of the lifting mast. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings: 
         FIG. 1  is a front perspective view of a lift device including a lifting mast and a collision control apparatus that controls the operation of the lifting mast for ensuring the safe operation of the lifting mast against collision of the lifting mast with an overhead obstruction; 
         FIG. 2  is a rear perspective view of the embodiment of  FIG. 1 ; 
         FIG. 3  is a side elevation view of the embodiment of  FIG. 1 ; 
         FIG. 4  is an enlarged fragmented view of the lifting mast of the lift of  FIG. 1  shown incorporating the collision control apparatus illustrated as it would appear in a neutral configuration; 
         FIG. 5  is a view similar to that of  FIG. 4  illustrating the collision control apparatus as it would appear in a safe configuration; 
         FIG. 6  is a top perspective view of the collision control apparatus of  FIG. 1 ; 
         FIG. 7  is a side elevation view of the embodiment of  FIG. 5 ; 
         FIG. 8  is an end elevation view of the embodiment of  FIG. 6 ; 
         FIG. 9  is a bottom perspective view of the embodiment of  FIG. 6 ; 
         FIG. 10  is a top perspective view of the embodiment of  FIG. 6  with portions thereof being broken away for illustrative purposes; 
         FIG. 11  is a bottom perspective view of the embodiment of  FIG. 10 ; 
         FIG. 12  is a side elevation view of the embodiment of  FIG. 10 ; 
         FIGS. 13 and 14  bottom perspective views of the embodiment of  FIG. 6  with portions thereof being broken away for illustrative purposes; 
         FIG. 15  is an exploded perspective view of a base assembly of the embodiment of  FIG. 6 ; 
         FIG. 16  is an exploded perspective view of a linkage assembly of the embodiment of  FIG. 6 ; 
         FIG. 17  is a side elevation view of the lift device of  FIG. 1  illustrating the lifting mast as it would appear in a lifted or raised position and further illustrating an obstruction located above the collision control apparatus and the lifting mast; 
         FIG. 18  is fragmented front elevation view of the embodiment of  FIG. 17  illustrating the obstruction located above the collision control apparatus and the lifting mast; 
         FIG. 19  is a side elevation view of the lift device similar to that of  FIG. 17  illustrating the lifting mast as it would appear in a lifted or raised position and further illustrating an obstruction located above the collision control apparatus and the lifting mast and the obstruction is further shown as it would appear contact encountering and deflecting the collision control apparatus; 
         FIG. 20  is a fragmented front elevation view of the embodiment of  FIG. 19  illustrating the obstruction contact encountering and deflecting the collision control apparatus; and 
         FIGS. 21 and 22  bottom perspective views of the embodiment of the collision control apparatus of  FIG. 18  shown as it would appear deflected, with portions thereof being broken away for illustrative purposes. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, in which like reference characters indicate corresponding elements throughout the several views, attention is first directed to  FIG. 1  illustrating a lift device  50  consisting of a lifting mast  51  mounted to a wheeled chassis  52  for reciprocal movement in lowering and raising/lifting directions between a lowered position or configuration as shown in  FIG. 1 , and a lifting, lifted or raised position or configuration as shown in  FIGS. 17 and 19 . Referencing  FIG. 1 , lifting mast  51  is a raising and lowering mast of lift device  50 , and extends vertically upright to an upper end or top  53  at the extreme upper extremity of lift device  50 . Lift device  51  incorporates a drive assembly denoted generally at  55  in  FIGS. 1-3 . Drive assembly  55  is not shown in detail and is an entirely conventional and well-known motorized drive assembly carried by wheeled chassis  52  and is conventionally operable for moving lifting mast  51  in the lifting or raising direction indicated by arrowed line A and the opposite lowering direction indicated by arrowed line B. Drive assembly  55  is operated by an operator interface in the form of a control panel  56 , which is formed in the rear of wheeled chassis  52  of lift device  50 . Drive assembly  55  incorporates a lifting circuit operable for engaging drive assembly  55  for moving lifting mast  51  in the raising direction in response operator control at control panel  56 , and incorporates a lowering circuit operative for engaging drive assembly  55  for moving lifting mast  51  in the lowering direction in response to operator control at control panel  56 . These lifting and lowering circuits are different from one another and are conventional and are activated in response to the operation of lift device  50  from control panel  56 . A support fixture or platform  57  is attached to lifting mast  51 , and movement of lifting mast  51  in the lifting and lowering directions between the raised and lowered positions of lifting mast  51  causes a corresponding movement of support platform  57  in lifting and lowering directions between a lowered position of support platform  57  in the lowered position of lifting mast  51  as shown in  FIGS. 1-3  and a raised or lifted position of support platform  57  in the raised or lifted position of lifting mast  51  as shown in  FIGS. 17 and 19  for facilitating the lifting and lowering of a load, such as equipment or material, placed on support platform  57 . Wheeled chassis  52  is characterized in that it is formed with wheels  58  to permit wheeled movement of lift device  50  laterally across the ground, the floor, or other surface. Two or more of wheels  58  are steerable. The operation of lift device  50  is controlled by hand and from control panel  56 , which permits movement of lifting mast  51  in the lowering and raising directions and which permits lift device  50  to be moved laterally according to the needs of the worker. Lift device  50  is generally representative of a conventional and well-known lifting device, further details of which will readily occur to the skilled artisan and will not be discussed in further detail. 
     According to the principle of the invention, lift device  50  is formed with an attached collision control apparatus denoted generally at  70  in  FIGS. 1-5 , which controls the operation of lifting mast  51  for ensuring the safe operation of lifting mast  51  against collision of lifting mast  51  with an overhead obstruction that lifting mast  51  could encounter response to movement of lifting mast  51  in the lifting direction toward an overhead obstruction. Collision control apparatus  70  is attached to top  53  of lifting mast  51 , and adjusts between a neutral configuration as shown in  FIGS. 4, 17, and 18 , and a safe configuration as shown in  FIGS. 5, 19, and 20  in response to collision control apparatus  70  contact encountering, i.e. contacting, an overhead obstruction denoted at  40  in  FIGS. 19 and 20 , which is an overhead obstructing surface in the present example formed, for example, by an overhead beam, duct, or the like. According to the principle of the invention, collision control apparatus  70  is operatively coupled to drive assembly  55  referenced in  FIGS. 1-3  such that drive assembly  55  is enabled for moving of lifting mast  51  in the lifting direction indicated by arrowed line A in  FIG. 1  to the lifting, lifted, or raised position of lifting mast  51  shown in  FIGS. 17-20  and the lowering direction indicated by arrowed line B in  FIG. 1  to the lowered position of lifting mast  51  shown in  FIGS. 1-3  in the neutral configuration of collision control apparatus  70  as shown in  FIGS. 1-4, 17, and 18 , drive assembly  55  is enabled for moving lifting mast in the lowering direction indicated by arrowed line B in  FIG. 1  to the lowered position of lifting mast  51  shown in  FIGS. 1-3  in the safe configuration of collision control apparatus  70  as shown in  FIG. 5 , and drive assembly  55  is disabled for moving lifting mast  51  in the lifting direction indicated by arrowed line A in  FIG. 1  in the safe configuration of collision control apparatus  70  as shown in  FIGS. 5, 19, and 20 . In the neutral configuration of collision control apparatus  70  illustrated in  FIG. 4 , drive assembly  55  is enabled to be operated from control panel  56  for moving lifting mast  51  in the lowering and lifting directions for lifting and lowering equipment or material or other load applied to support platform  57  in the normal operation of lift device  50 . In the safe configuration of collision control apparatus  70  as shown in  FIG. 5  in response to collision control apparatus  70  contact encountering an overhead obstruction, collision control apparatus  70  disables drive assembly  55  from moving lifting mast  51  in the lifting direction stopping movement of lifting mast  51  in the lifting direction and further disables drive assembly from being operated from control panel  56  for moving lifting mast  51  in the lifting direction thereby preventing an unwanted collision from occurring at top  53  of lifting mast  51  that could cause damage to lifting mast  51  or to the load carried by support platform  57  and furthermore preventing an operator from inadvertently operating the drive assembly  55  in the lifting direction that again could cause damage to lifting mast  51  and to a load carried by support platform  57 , but in the safe configuration of collision control apparatus  70  drive assembly  55  is enabled for moving lifting mast  51  in the lowering direction and drive assembly  55  is further enabled to be operated from control panel for moving lifting mast  51  in the lowering direction thereby allowing an operator to move lifting mast  51  in the lowering direction and away from the overhead obstruction, in accordance with the principle of the invention. And so in the neutral configuration of collision control apparatus  70  drive assembly  55  is operable for moving lifting mast in the lifting and lowering directions in the normal operation of lift device  50 , and in the safe configuration of collision control apparatus  70  drive assembly  55  is disabled for moving lifting mast  51  in the lifting direction to prevent a potentially catastrophic or dangerous collision in the movement of lifting mast  51  in the lifting direction, and is enabled for moving lifting mast  55  in the lowering direction to permit lifting mast  51  to be withdrawn from an overhead object or obstruction. 
     Looking to  FIG. 4 , collision control apparatus  70  is attached to top  53  of lifting mast  51 . Collision control apparatus  70  includes a head  71  positioned above and over top  53  of lifting mast  51 , and is mounted to lifting mast  51  for displacement/movement in reciprocal directions indicated by double arrowed line C between a raised neutral position shown in  FIGS. 4, 17, and 18  away from top  53  of lifting mast  51  and a lowered safe position shown in  FIGS. 5, 19, and 20  toward top  53  of lifting mast  51  in response to head  71  contact encountering an object/obstruction above top  53  of lifting mast  51  and head  71 , such as obstruction  40  in  FIGS. 19 and 20 , in response to movement of lifting mast  51  in the lifting direction of lifting mast  51 . Drive assembly  55 , referenced in  FIGS. 1-3 , is enabled for moving of lifting mast  51  in the lifting and lowering directions of lifting mast  51  in the neutral position of head  71  shown in  FIG. 4 , drive assembly  55  is enabled for moving lifting mast  51  in the lowering direction of lifting mast  51  in the safe position of head  71  as shown in  FIG. 5 , and drive assembly  55  is disabled for moving lifting mast  51  in the lifting direction of lifting mast  51  in the safe position of head  71  shown in  FIG. 5 , and all of this characterizes an operative coupling between head  71  of collision control apparatus  70  and drive assembly  55 . 
     In the neutral position of head  71 , collision control apparatus  70  is in the neutral configuration. In the safe position of head  71 , collision control apparatus  70  is in the safe configuration. A bias is applied to head  71  tending to bias head  71  from the safe position of head  71  defining the safe configuration of collision control apparatus  70  to the neutral position of head  71  defining the neutral configuration of collision control apparatus  70 . This applied bias holds head  71  in its neutral position defining the neutral configuration of collision control apparatus  70  in the absence of an applied force to head  71  in the form of a collision between head  71  and an overhead obstruction. In response to a force applied to head  71  in the form of a contact collision of head  71  with an overhead obstruction in response to movement of lifting mast in the lifting direction, the bias applied to head  71  is available to be overcome causing head  71  to move from the neutral position of head  71  defining the neutral configuration of collision control apparatus  70  to the safe position of head  71  defining the safe configuration of collision control apparatus  70 . The bias applied to head  71  acts on head  71  and urges head  71  from the safe position thereof to the neutral position thereof to reset head  71  from the safe position thereof to the neutral position thereof in the absence of an applied force to head  71  in the form of a collision between head  71  and an overhead obstruction. 
     Head  71  is mounted to lifting mast  51  for displacement between its neutral and safe positions with a linkage assembly  72  interacting between, or otherwise coupled between, head  71  and lifting mast  51 . Linkage assembly  72  is coupled between head  71  and top  53  of lifting mast  51 . Head  71  covers top  53  of lifting mast  51  so as to shield top  53  of lifting mast  51  from directly contacting or contact encountering an object or obstruction above top  53  of lifting mast  41  and head  71  causing head  71  to take the brunt of impact with such an object or obstruction above top  53  of lifting mast  51  and head  71 . 
     Head  71  is operatively coupled to drive assembly  55 , referenced in  FIGS. 1-3 , of lift device  50  with a switch  73 , which, in turn, is operatively coupled to drive assembly  55 . Switch  73 , referenced in  FIGS. 4 and 5 , is operatively coupled to drive assembly  55 , referenced in  FIGS. 1-3 , with conventional electrical wiring denoted generally at  74  in  FIGS. 4 and 5 . Switch  73  is coupled to interact between head  71  and top  53  of lifting mast  51  so as to be moved between deactivated and activated positions enabling drive assembly  55  for moving lifting mast  51  in the lifting and lowering directions of lifting mast  51  in the neutral position of head  71  shown in  FIG. 4  corresponding to the deactivated position of switch  73 , disabling drive assembly for moving lifting mast in the lifting direction of lifting mast  51  in the safe position of head  71  shown in  FIG. 5  corresponding to the activated position of switch  73 , and enabling drive assembly  55  for moving lifting mast  51  in the lowering direction of lifting mast  51  in the safe position of head  71  corresponding to the activated position of switch  73 . Because switch  73  limits the operation of drive assembly  55  when switch  73  is activated, namely, disables drive assembly  55  from moving lifting mast  51  in the lifting direction while allowing drive assembly  55  to operate for moving lifting mast  51  in the lowering direction, switch  73  is considered a limit switch. 
     Collision control apparatus  70  incorporates a base  75  shown in  FIG. 4 , which is removably coupled to top  53  of lifting mast  51 . Base  75  is used to removably couple collision control apparatus  70  to top  53  of lifting mast  51 . Linkage assembly  72  is coupled between base  75  and head  71  and couples base  75  to head  71  and thus couples head  71  with respect to top  53  of lifting mast  51 . Switch  73  is attached to and is carried by base  75 . Base  75  is positioned between top  53  of lifting mast  51  and head  71 , and head  71  is positioned above and over not only top  53  of lifting mast  51  but also base  75  of collision control apparatus  70  and linkage assembly  72 . Head  71  is mounted to base  75  with linkage assembly  72  that interacts between head  71  and base  75  for facilitating the displacement or movement of head  71  between the raised neutral position of head  71  away from base  75  and top  53  of lifting mast  51  defining the neutral configuration of collision control apparatus  70  and the lowered safe position of head  71  toward base  75  and top  53  of lifting mast  51  defining the safe configuration of collision control apparatus  70  in response to head  71  contact encountering an object or obstruction above base  75 , top  53  of lift device  50 , and head  71 . With switch  73  attached to base  75 , switch  73  interacts between head  71  and base  75  enabling drive assembly  55  for moving lifting mast  51  in the lifting and lowering directions of lifting mast  51  in the neutral position of head  71  shown in  FIG. 4 , disabling drive assembly for moving lifting mast in the lifting direction of lifting mast  51  in the safe position of head  71  shown in  FIG. 5 , and enabling drive assembly  55  for moving lifting mast  51  in the lowering direction of lifting mast  51  in the safe position of head  71 . 
       FIGS. 6-14  illustrate various views of collision control apparatus  70 . Referencing  FIGS. 6-14  in relevant part in conjunction with the ensuing discussion, collision control apparatus  70  consists of four main parts, namely, head  71 , base  75 , linkage assembly  72  interposed between head  71  and base  75  coupling head  71  to base  75 , and switch  73  attached to base  75 , all of which have been initially introduced above. Base  75  is configured to be removably coupled to top  53  of lifting mast  51  referenced in  FIGS. 1-5 , which joins collision control apparatus  70  to top  53  of mast  51  as to be readily separable from top  53  of mast  51 , such as for repair and maintenance. Collision control apparatus  70  extends upwardly from top  53  of lifting mast  51  from base  75  removably coupled to top  53  of lifting mast  51  to linkage assembly  72  and then to head  71 . 
     Head  71  is a broad, inverted, tray-like body fashioned of plastic, wood, metal, or other material or combination of materials having the properties of rigidity, resiliency, and resistance to impacts. Head  71  is preferably integrally formed, such as through molding or machining, and may, in the alternative, be fashioned of a plurality of parts attached with joinery, such as welding, adhesive, heat bonding, or the like. Head  71  is generally rectangular in overall shape and includes a flat part or plate  80  having opposed outer and inner faces  80 A and  80 B, a perimeter extremity  81  and a continuous sidewall  82  depending downwardly from perimeter extremity  81  and which terminates downwardly with a perimeter edge  83  defining an opening  84  leading upwardly into a volume  85  bound or otherwise defined by inner face  80 A of flat part  80  and continuous sidewall  82 . Head  71  is formed with an attached abutment  86 , which is an elongate post that is rigidly affixed to inner face  80 B of flat part  80  and which depends downwardly therefrom through volume  85  and opening  84  to an outer end  87 . Abutment  86  is elongate and has a length extending from its attachment point to inner face  80 B of flat part  80  of head  71  to outer end  87 . Base  75  is located under and opposes opening  84  and volume  85  of head  71 , linkage assembly  72  is coupled between head  71  and base  75 , and abutment  86  is positioned to interact with switch  73  in response to movement of head  71  between its raised neutral position and its lowered safe position for deactivating and activating switch  73 . 
     Base  75  forms part of a base assembly of collision control apparatus  70 , which principally includes base  75  and switch  73  attached to base  75 .  FIG. 15  is an exploded perspective view of the base assembly illustrating base  75  and switch  73 . Referring to  FIG. 15  and referring in relevant part to  FIGS. 6-14 , base  75  is a broad, tray-like body that is generally rectangular in shape and that in size is smaller than head  71  permitting base  75  to pass into volume  85  of head  71  through opening  84  of head  71  disclosed and discussed above in response to movement of head  71  between the neutral and safe positions thereof with respect to base  75 . Base  75  is fashioned of plastic, wood, metal, or other material or combination of materials having the properties of rigidity, resiliency, and resistance to impacts. Base  75  is preferably integrally formed, such as through molding or machining, and may, in the alternative, be fashioned of a plurality of parts attached with joinery, such as welding, adhesive, heat bonding, or the like. Base  75  has opposed ends  90  and  91 , opposed sides  92  and  93  extending between opposed ends  90  and  91 , a middle between ends  90  and  91  denoted generally at  94 , a top side  95 , and an opposed bottom side or underside  96  referenced in  FIG. 14 . A transverse channel  97  is formed at middle  94  in top side  95  of base  75 , which is parallel with respect to ends  90  and  91  and which extends from side  92  of base  75  to side  93  of base  75 . An abutment-receiving opening  98  that receives therethrough and accommodates abutment  86  of head  71  is formed through base  75  near side  92  between sides  92  and  93 , and is positioned between channel  97  and end  90 . 
     Ends  90  and  91  of base  75  are each fashioned with an attached strap  100  used to removably couple base  75  to top  53  of lifting mast  51 . Straps  100  each have opposed lugs  101  depending downwardly from either end of strap  100  on either of sides  92  and  93  of base  75 , which receive fasteners, such as set screws, used to removably couple base  75 , and thus collision control apparatus  70 , to top  53  of lifting mast  51  of lift device  50  discussed in conjunction with  FIGS. 1-3 . Straps  100  are parallel with respect to each other and are transverse with respect to the long axis of base  75  extending from end  90  to end  91 . Like base  75 , straps  100  and  101  are each fashioned of plastic, wood, metal, or other material or combination of materials having the properties of rigidity, resiliency, and resistance to impacts. Straps  100  are received along the underside  96  of base  75  at the corresponding ends  90  and  91  of base  75 , are received in corresponding seats  103  form near ends  90  and  91  in underside  96  of base  75 , and are each removably coupled to base  75  with a threaded fastener  105  that extends through an opening  106  in strap  101  between lugs  101  and which is threaded into a threaded opening in base  75 . A washer  108  is applied onto threaded fastener  105  between each strap  100  and the head of the corresponding threaded fastener  105  to give tightness to the joint when the threaded fastener  105  is tightened. With straps  100  so attached to base  75  along the underside  96  of base  75 , the corresponding lugs  101  depending downwardly with respect to straps  100  and underside  86  of base  75 . To removably secure base  75  to top  53  of lifting mast  51  as shown in  FIG. 4 , base  75  is placed underside  96  (not shown in  FIG. 4 ) down onto top  53  of lifting mast  51  positioning the underside of straps  100  onto either side of top  53  of lifting mast  51  and locating lugs  101  along the front and rear sides of lifting mast  51  and that are identically secured to lifting mast with set screws  60  that are received through openings in lugs  60  and which are tightened down against mast  51  securing base  75  in place. 
     Switch  73  is an entirely conventional and well-known switch, which includes a spring-loaded plunger  110  and a switch body  111  containing a conventional and well-known toggle switch, which is activated and deactivated in response to movement of plunger  110  in reciprocal directions as indicated by double arrowed line D between an extended position as shown in  FIG. 15  deactivating switch  73  and a depressed position as shown in  FIG. 21  activating switch. Switch  73  referenced in  FIGS. 4 and 5  is operatively coupled to the lifting circuit of drive assembly  55 , referenced in  FIGS. 1-3 , with conventional electrical wiring denoted generally at  74  in  FIGS. 4 and 5 . In the extended position of plunger  110  deactivating switch  73 , the lowering and lifting circuits of drive assembly  55  are enabled thereby enabling drive assembly  55  for moving lifting mast  51  in the lifting and lowering directions of lifting mast  51  thereby enabling drive assembly  55  to be operated from control panel  56  for moving lifting mast  51  in the lifting and lowering directions. In the depressed position of plunger  110  activating switch  73 , the lifting circuit of drive assembly  5  is disabled by switch  73  disabling drive assembly  55  for moving lifting mast in the lifting direction of lifting mast  51  thereby disabling drive assembly  55  from being operated from control panel  56  for moving lifting mast  51  in the lifting direction, and the lowering circuit of drive assembly  55  remains unaffected and is thereby enabled for moving lifting mast  51  in the lowering direction of lifting mast  51  thereby enabling drive assembly  55  to be operated from control panel  56  for moving lifting mast  51  in the lowering direction. The coupling between switch  73  and the lifting circuit of drive assembly  55  via wiring  74  is formed through conventional wiring techniques well within the skill and knowledge of a skilled electrician. 
     Switch  73  is received along the underside  96  of base  75  between sides  92  and  93  of base  75  and between opening  98  and end  90  of base  75  including strap  100  removably coupled to end  90  of base  75 , and is located between top  53  of mast  51  and underside  96  of base  75  removably coupled to upper end  53  of lifting mast  51  as shown in  FIG. 4 . Switch body  111  is received against underside  96  of base  75  and is removably coupled to base  75  with threaded fasteners  115  that extends through corresponding openings  116  in switch body  111  and corresponding openings  117  in base  75 , and which are threaded into corresponding nuts  118 , which are received captured in openings  117  from top side  95  of base  75  and which are tightened to secure switch  73  in place along underside  96  of base  75 . Washers  119  are applied onto threaded fasteners  115  in openings  117  between nuts  118  received in openings  118  and base  75  to give tightness to the joints when nuts  118  are tightened onto threaded fasteners  115 . Plunger  110  extends away from switch body  111  toward middle  94  of base  75 , and is located under opening  98  as shown in  FIG. 14  and is registered with respect to opening  98 . Head  71  is mounted to the described base assembly of collision control apparatus  70  for movement between its neutral and safe positions with linkage assembly  72 , and the base assembly is, in turn, removably coupled to top  53  of lifting mast  51  as shown in  FIG. 4 . 
     Linkage assembly  72  is interposed between head  71  and base  75  as best seen in  FIGS. 10-14 , couples head  71  to base  75 , and articulates between extended and collapsed positions, orientations, or states to permit head  71  to move between its raised neutral position away from base  75  and its lowered safe position toward base  75 . In the raised neutral position of head  71 , linkage assembly  72  is extended or is otherwise in an extended orientation or state. In the lowered safe position of head  71 , linkage assembly  72  is collapsed or is otherwise in a collapsed orientation or state. In response to movement of head  71  from its raised neutral position away from base  75  to is lowered safe position toward base  75 , linkage assembly  72  articulates from its extended position, orientation, or state to its collapsed position, orientation, or state and collapses into volume  85  of head  71  through opening  84  and base  75  passes through opening  84  into volume  85 . In response to movement of head  71  from its lowered safe position to its raised neutral position, linkage assembly  72  articulates from its collapsed position, orientation, or state to its extended position, orientation, or state and linkage assembly  72  and base  75  extend outwardly from volume  85  through opening  84  to base  75 . 
     In the attachment of head  71  to base  75  with linkage assembly  72 , abutment  86  registers with opening  98  formed through base  75  and extends downwardly from inner face  80 B of head  71  through volume  85  and opening  84  of head  71  and through opening  98  of base  75  as seen in  FIG. 14  to outer end  87 , which is located under the underside  96  of base  75  and which opposes and confronts abutment  110  of switch  73 . Abutment  86  of head  71  passes through opening  98  of base  75  and reciprocates through opening  98  of base  75  in response to movement of head  71  between its raised neutral position and its lowered safe position. In the raised neutral position of head  71  as shown in  FIGS. 4, 7 , and  9 - 14 , outer end  87  of abutment  86  confronts abutment  110  of switch  73  and abutment  110  is in its extended position deactivating switch  73 . 
     In response to movement of head  71  from its raised neutral position as shown in  FIGS. 4, 7, 9-14 , to is lowered safe position as shown in  FIGS. 5, 21, and 22 , abutment  86  is driven downwardly toward base  75  and switch  73 , and outer end  87  of abutment  86  encounters and is driven against plunger  100  depressing plunger  110  from its extended position to its depressed position as shown in  FIGS. 21 and 22  activating switch  73 . Switch  73  is activated with minimal displacement of head  71  from its raised or neutral position into and toward its lowered safe position causing outer end  87  of abutment  86  to encounter and depress plunger  100 , and abutment  86  interacts with plunger  110  along the length of abutment  86  from its attachment point to inner face  80 B of flat part  80  of head  71  to outer end  87  and keeps plunger  110  depressed activating switch  73  along the path of displacement of head  71  from its raised neutral position to its lowered safe position, according to the principle of the invention. 
     The length of abutment from its attachment point to inner face  80 B of flat part  80  of head  71  to outer end  87  provides for over-travel of head  71  from its raised neutral position to its lowered safe position while maintaining the depression of plunger  110  by abutment  86  along the length of abutment  86  from its attachment point to inner face  80 B of flat part  80  of head  71  to the outer end  87  of abutment, and this over-travel of head  71  from its raised neutral position to its lowered safe position provides play in the form of an over-travel distance or buffer zone between the raised neutral position of head  71  and the lowered safe position of head  71  to prevent damage to head  71  and to collision control apparatus  70  as a whole and also to lifting mast  51  and to the overhead obstruction encountered by head  71 . Plunger  110  is depressed activating switch  73  in response to an initial interaction of outer end  87  of abutment  86  against plunger  100  caused in response to displacement of head  71  from its raised neutral position into or otherwise toward its lowered safe position, and abutment  86  interacts with plunger  110  along the over-travel distance or buffer zone defined by the length of abutment  86  to ensure plunger  110  remains depressed and switch  73  remains activated along the over-travel distance or buffer zone. In the present embodiment as a matter of example, length of abutment  86  from its attachment point to inner face  80 B of flat part  80  of head  71  to outer end  87  is approximately three inches, which defines an over-travel distance or buffer zone of head  71  between its raised neutral position and its lowered safe position of this distance of approximately three inches. Depending on specific needs or applications, the length of abutment  86  can be less than approximately three inches or greater than approximately three inches to define other over-travel distance or buffer zones of head  71  as may be desired. 
     In response to movement of head  71  from its lowered safe position as shown in  FIGS. 21 and 22  to its raised safe position as shown in  FIGS. 4, 7, 9-14 , abutment  86  is driven upwardly away from base  75  and switch  73 , and is driven upwardly away from plunger  110  moving abutment  86  out of its interaction with plunger  110  thereby un-depressing plunger  110  and permitting plunger  110  to move from its depressed position to its extended position deactivating switch  73 . The interaction between abutment  86  of head  71  and plunger  110  of switch  73  forms an operative coupling between head  71  and switch  73  causing switch  73  to switch between its deactivated and activated positions in response to movement of head  71  between its raised neutral position and its lowered safe position, and switch  73  interacting between base  75  and head  71  forms an operative coupling of head  71  of collision control apparatus  70  to drive assembly  55 . 
     Referring to  FIGS. 10-14  in relevant part, and to  FIG. 16  illustrating an exploded perspective view of linkage assembly  72 , linkage assembly  72  is a scissor linkage that articulates between extended and collapsed positions, orientations, or states, and consists of opposed, identical folding scissor mechanisms  130 A and  130 B linked together with elongate connecting rods including upper connecting rods  140 , lower connecting rods  141 , and a central connecting rod  142 . Upper connecting rods  140  of linkage assembly  72  are pivoted, i.e. pivotally attached, to head  71 , and lower connecting rods  141  of linkage assembly  72  are pivoted, i.e. pivotally attached, to base  75 . 
     Scissor mechanisms  130 A and  130 B are the mirror image opposites of one another and each include a pair of identical elongate members  131  and  132  arranged in a cross-cross pattern. Elongate members  131  each have opposed upper and lower ends  131 A and  131 B, and a middle  131 C, and elongate members  132  each have opposed upper and lower ends  132 A and  132 B, and a middle  132 C. One upper connecting rod  140  connects upper ends  131 A of elongate members  131  and is pivoted to head  71 , the other upper connecting rod  140  connects upper ends  132 A of elongate members  132  and is pivoted to head  71 , one lower connecting rod  141  connects lower ends  131 B of elongate members  131  and is pivoted to base  75 , and the other lower connecting rod  141  connects lower ends  132 B of elongate members  132  and is pivoted to base  75 . Elongate members  131  and  132  of each scissor mechanism  130 A and  130 B cross-cross at their respective middles  131 C and  132 C, and central connecting rod  142  pivotally connects the middles  131 C and  132 C the corresponding scissor mechanisms  130 A and  130 B and connects the middles  131 C and  132 C of one scissor mechanism  130 A to the middles  131 C and  132 C of the opposed scissor mechanism  130 B to about which scissor assemblies  130 A and  13 B are permitted to pivot between extended and collapsed conditions of linkage assembly  72  in response to the corresponding movement or displacement of head  71  between its neutral and safe positions. 
     Upper connecting rods  140  extend along inner face  80 B of flat part  80  of head  71 , and opposed lower connecting rods  141  extend along underside  96  of base  75 . The opposed ends of upper connecting rod  140  connecting upper ends  131 A of elongate members  131  extend through corresponding identical openings  120  formed in opposed tabs  121  attached to and depending downwardly from inner face  80 B of flat part  80  of head  71  as best shown in  FIG. 13 , and then into openings in the corresponding upper ends  131 A of elongate members  131 , and are retained by corresponding clips  150  and washers  151  applied to the respective ends of upper connecting rod  140  on the outer sides of the respective tabs  121  connecting upper ends  131 A of elongate members  131  together and to head  71 . The opposed ends of upper connecting rod  140  connecting upper ends  132 A of elongate members  132  extend through corresponding identical openings  122 , which are elongated, formed in opposed tabs  123  attached to and depending downwardly from inner face  80 B of flat part  80  of head  71  as best shown in  FIG. 13 , and then into openings in the corresponding upper ends  132 A of elongate members  132 , and are retained by corresponding clips  150  and washers  151  applied to the respective ends of upper connecting rod  140  on the outer sides of the respective tabs  123  connecting upper ends  132 A of elongate members  132  together and to head  71 . 
     The opposed ends of lower connecting rod  141  connecting lower ends  131 B of elongate members  131  extend through corresponding identical openings  125  formed in sides  92  and  93  of base  75  near end  91  of base  75  between strap  100  attached to end  91  of base  75  and middle  94  of base  75  as best shown in  FIG. 13 , and then through openings in the corresponding lower ends  131 B of elongate members  131 , and are retained by corresponding clips  150  and washers  151  applied to the respective ends of lower connecting rod  141  along the outer sides of the respective sides  92  and  93  of base  75  connecting lower ends  131 B of elongate members  131  together and to base  75 . The opposed ends of lower connecting rod  141  connecting lower ends  132 B of elongate members  132  extend through corresponding identical openings  126 , which are elongated, formed in sides  92  and  93  of base  75  near end  90  of base  75  between strap  100  attached to end  90  of base  75  and middle  94  of base  75 , and then through openings in the corresponding lower ends  132 B of elongate members  132 , and are retained by corresponding clips  150  and washers  151  applied to the respective ends of lower connecting rod  141  along the outer sides of the respective sides  92  and  93  of base  75  connecting lower ends  132 B of elongate members  132  together and to base  75 . 
     The opposed ends of upper connecting rod  140  connecting upper ends  131 A of elongate members  131  are free to pivot in openings  120  of head  71 , the opposed ends of upper connecting rod  140  connecting upper ends  132 A of elongate members  132  are free to pivot in openings  122  of head  71 , the opposed ends of lower connecting rod  141  connecting lower ends  131 B of elongate members  131  are free to pivot in openings  125  of base  75 , and the opposed ends of lower connecting rod  141  connecting lower ends  132 B of elongate members  132  are free to pivot in openings  126  of base  75 . Accordingly, the opposed ends of upper connecting rod  140  connecting upper ends  131 A of elongate members  131  are pivotally attached to head  71 , the opposed ends of upper connecting rod  140  connecting upper ends  132 A of elongate members  132  are pivotally attached to head  71 , the opposed ends of lower connecting rod  141  connecting lower ends  131 B of elongate members  131  are pivotally attached to base  75 , and the opposed ends of lower connecting rod  141  connecting lower ends  132 B of elongate members  132  are pivotally attached to base  75 . 
     One end of central connecting rod  142  extends through aligned corresponding openings in middles  131 C and  132 C of elongate members  131  and  132  of scissor mechanisms  130 A and is retained by clip  150  and washer  151 , and the other end of central connecting rod  142  extends through aligned corresponding openings in middles  131 C and  132 C of elongate members  131  and  132  of the opposed scissor mechanisms  130 B and is retained by clip  150  and washer  151 . A washer  151  is applied onto central connecting rod  142  between middles  131 C and  132 C of scissor mechanism  130 A, and a washer  151  is applied onto central connecting rod  142  between middles  131 C and  132 C of elongate members  131  and  132  of scissor mechanism  130 B. A stay  160  is secured to and between elongate members  131  of scissor mechanisms  130 A and  130 B between upper ends  131 A of elongate members  131  and middles  131 C and  131 C of elongate members  131 , and an identical stay  160  is secured to and between elongate members  132  of scissor mechanisms  130 A and  130 B between upper ends  132 A of elongate members  132  and middles  132 C and  132 C of elongate members  132 . The opposed ends of stay  160  coupled between elongate members  131  of scissor mechanisms  130 A and  130 B are affixed to elongate members  131  of scissor mechanisms  130 A and  130 B with threaded fasteners  161 , and the opposed ends of stay  160  coupled between elongate members  132  of scissor mechanisms  130 A and  130 B are affixed to elongate members  132  of scissor mechanisms  130 A and  130 B with threaded fasteners  161 . Stays  160  impart structural rigidity to linkage assembly  72 . 
     Linkage assembly  72  is exemplary of a conventional scissor linkage assembly, whereby the identical folding scissor mechanisms  130 A and  130 B are linked together with elongate upper connecting rods  140  pivotally attached to head  71 , lower connecting rods  141  pivotally attached to base  75 , and central connecting rod  142  pivotally attaching middles  131 C and  132 C of elongate members  131  and  132  of scissor mechanism  130 A to middles  131 C and  132 C of elongate members  131  and  132  of scissor mechanism  130 B. Linkage assembly  72  is somewhat shortened in the extended position thereof corresponding to the neutral position of head  71 , and is somewhat lengthened in the collapsed position thereof corresponding to the safe position of head  71 . The elongation of openings  122  of head  71  and openings  126  of base  75  accommodate the lengthening and shortening of linkage assembly  72  in response to movement of linkage assembly  72  between its extended and collapsed positions, and ensures that linkage assembly  72  is free to move without restriction between its extended and collapsed positions in response to movement of head  71  between its neutral and safe positions. 
     According to the principle of the invention, linkage assembly  72  is fashioned with a tension spring  170 . Tension spring  170  consists of a wire formed into coils  171  encircling central connecting rod  142  between, one the one hand, middles  131 C and  132 C of scissor mechanism  130 A, and, on the other hand, middles  131 C and  132 C of scissor mechanism  130 B. The opposed outermost coils of coils  171  of tension spring  170  lead to tag ends  172  and  173 , respectively. Tag end  172  is directed upwardly toward upper ends  132 A of elongate members  132  of scissor mechanisms  130 A and  130 B, and tag end  173  is directed oppositely and downwardly toward lower ends  132 B of elongate members  132  of scissor mechanisms  130 A and  130 B. To retain tension spring  170  in place to central connecting rod  142 , a clip  150  and a washer  151  are applied over central connecting rod  142  between the outermost coil of tension spring  170  formed with tag end  172  and middle  132 C of elongate member  132  of scissor mechanism  130 A, and a corresponding clip  150  and a washer  151  are applied over central connecting rod  142  between the outermost coil of tension spring  170  formed with tag end  173  and middle  132 C of elongate member  132  of scissor mechanism  130 B. Tension spring  170  is fashioned of spring steel, a nickel-based spring alloy, or other material or combination of materials having a substantially constant moduli of elasticity as is typical with tension springs. 
     Tag end  172  not only is directed upwardly toward upper ends  132 A of elongate members  132  of scissor mechanisms  130 A and  130 B, tag end  172  is also directed upwardly toward and directly contacts inner face  80 B of head  71  as shown in  FIG. 11 . Tag end  173  not only is directed oppositely and downwardly toward lower ends  132 B of elongate members  132  of scissor mechanisms  130 A and  130 B, tag end  173  is also directed downwardly toward and directly contacts top side  95  of base  75 . The direct contact of tag end  172  to inner face  80 B of head  71  constitutes a coupling of tag end  172  of spring  170  to head  71 , and the direct contact of tag end  173  to top side  95  of base  75  constitutes a coupling of tag end  172  of spring  170  to base  75 . The coupling of tag end  172  of spring  170  to head  71  and the coupling of tag end  173  of spring to base  75  causes spring  170  to act between head  71  and base  75  biasing head  71  away from the safe position of head  71  toward base and toward the neutral position of head  71  away from base  75 , whereby coils  171  of spring  170  wind and unwind in response to movement of head  71  between its raised neutral position and its lowered safe position relative to base  75 . Thus, spring  170  acts between head  71  and base  75  applying a bias to head  71  tending to bias head  71  from the lowered safe position of head  71  defining the safe configuration of collision control apparatus  70  to the raised neutral position of head  71  defining the neutral configuration of collision control apparatus  70 . 
     The described bias applied by spring  170  attached to linkage assembly  72  and which is coupled between head  71  and base  75  tends to holds head  71  in its raised neutral position defining the neutral configuration of collision control apparatus  70  in the absence of a collision between head  71  and an overhead obstruction. In response to a contact collision of head  71  with an overhead obstruction in response to movement of lifting mast  51  in the lifting direction sufficient to overcome the bias applied to head  71  by spring  170 , the bias applied to head  71  by spring  170  is overcome causing head  71  to move/displace from the neutral position of head  71  defining the neutral configuration of collision control apparatus  70  to the safe position of head  71  defining the safe configuration of collision control apparatus  70 . In this embodiment, spring  170  applies a force of approximately two pounds against head  71  to hold head  71  in its neutral position. The force of the impact of head  71  with an overhead obstruction sufficient to overcome the bias applied by spring  170  is thus only about two pounds. As such, the amount of force applied to head  71  sufficient to overcome the bias applied by spring  170  to cause head  71  to move/displace from the neutral position of head  71  defining the neutral configuration of collision control apparatus  70  to the safe position of head  71  defining the safe configuration of collision control apparatus  70  is a low amount of force representing a soft impact of head  71  with an overhead obstruction at issue. In other words, in the present embodiment it takes only about two pounds of force applied to head  71  to overcome the low/soft bias of spring  170  to result in the movement/displacement of head  71  from the neutral position of head  71  defining the neutral configuration of collision control apparatus  70  to the safe position of head  71  defining the safe configuration of collision control apparatus  70 . 
     In response to removing the applied force to head  71 , the bias applied by spring  170  is responsive and moves head  71  from its lowered safe position to its raised neutral position so as to reset head  71  back into its raised neutral position. The elongation of openings  122  of head  71  and openings  126  of base  75  not only accommodates the lengthening and shortening of linkage assembly  72  in response to movement of linkage assembly  72  between its extended and collapsed positions, but also constrains movement of linkage assembly  72  between its extended and collapsed positions so as to, in turn, constrain movement of head  71  between its neutral and safe positions. Channel  97  formed in base  75  opposes central connecting rod  142  extending between the middles  131 C and  132 C of the elongate members  131  and  132  of scissor mechanisms  130 A and  130 B and the coils  171  portion of spring  170  applied to central connecting rod  142  and receives and accommodates connecting rod  142  and the coils  171  portion of spring  170  in the collapsed position of linkage assembly  72  corresponding the lowered safe position of head  71  that, in turn, corresponds to the safe configuration of collision control apparatus  70 . 
     In sum, collision control apparatus  70  consists principally of head  71 , base  75  removably coupled to top  53  of lifting mast  51  of lifting device as shown in  FIG. 105 , linkage assembly  72  interposed between head  71  and base  75  coupling head  71  to base  75 , and switch  73  attached to base  75 . Collision control apparatus  70  extends upwardly from top  53  of lifting mast  51  from base  75  removably coupled to top  53  of lifting mast  51  to linkage assembly  72  and then to head  71 , which is located over top  53  of lifting mast  51  and which is held by linkage assembly  72  so as to be horizontal with respect to top  53  of lifting mast  51 . The conventional scissor architecture of linkage assembly  72  as herein specifically described holds head  71  horizontally with respect to top  53  of lifting mast  51  and maintains head  71  in this horizontal configuration while linkage assembly  72  articulates between its collapsed and extended positions. In response to a contact collision of head  71  with an overhead obstruction in response to movement of lifting mast  51  in the lifting direction sufficient to overcome the bias applied to head  71  by spring  170 , the bias applied to head  71  by spring  170  is overcome causing head  71  to move/displace from the neutral position of head  71  defining the neutral configuration of collision control apparatus  70  to the safe position of head  71  defining the safe configuration of collision control apparatus  70 . In response to movement of head  71  from its raised neutral position as shown in  FIGS. 4, 7, 9-14 , to is lowered safe position as shown in  FIGS. 5, 21, and 22 , abutment  86  is driven downwardly toward base  75  and switch  73 , and encounters and is driven against plunger  100  depressing plunger  110  from its extended position to its depressed position as shown in  FIGS. 21 and 22  activating switch  73 . In response to removing the applied force to head  71 , such as by moving lifting mast  51  in the lowering direction away from the overhead obstruction, the bias applied by spring  170  is responsive and moves head  71  from its lowered safe position to its raised neutral position so as to reset head  71  back into its raised neutral position. In response to movement of head  71  from its lowered safe position as shown in  FIGS. 21 and 22  to its raised safe position as shown in  FIGS. 4, 7, 9-14 , abutment  86  is driven upwardly away from base  75  and switch  73 , and is driven upwardly away from plunger  110  un-depressing plunger  110  permitting plunger  110  to move from its depressed position to its extended position deactivating switch  73 . 
     And so in the raised neutral position of head  71 , collision control apparatus  70  is in its neutral configuration and switch  73  is deactivated enabling the lifting and lowering circuits of drive assembly  55  thereby fully enabling drive assembly  55  in the normal operation of lift device  50  for moving of lifting mast  51  in the lifting direction indicated by arrowed line A in  FIG. 1  to the lifting, lifted, or raised position of lifting mast  51  shown in  FIGS. 17-20  and the lowering direction indicated by arrowed line B in  FIG. 1  to the lowered position of lifting mast  51  shown in  FIGS. 1-3  as shown in  FIGS. 1-4, 17 , and  18  for lifting and lowering equipment or material or other load applied to support platform  57  in the normal operation of lift device  50 . Again, in the neutral configuration of collision control apparatus  70 , drive assembly  55  is enabled to be operated from control panel  56  for moving lifting mast  51  in the lowering and lifting directions for lifting and lowering equipment or material or other load applied to support platform  57  in the normal operation of lift device  50 . In the lowered safe position of head  71 , collision control apparatus  70  is in its safe configuration and switch  73  is activated partially enabling drive assembly  55  by disabling the lifting circuit of drive assembly  55  to disable drive assembly  55  from moving lifting mast  51  in the lifting direction indicated by arrowed line A in  FIG. 1  stopping movement of lifting mast  51  in the lifting direction while leaving the lowering circuit of drive assembly  55  enabled to enable drive assembly  55  to move lifting mast  55  in the lowering direction. Again, in the safe configuration of collision control apparatus  70 , drive assembly  55  is enabled to be operated from control panel  56  for moving lifting mast  51  in the lowering direction for moving lifting mast  51  away from an overhead obstruction to thus permit lifting mast  51  to be withdrawn from an overhead object or obstruction, and drive assembly  55  is disabled to be operated from control panel  56  for moving lifting mast in the lifting direction to prevent damage to lifting mast  51  or to the load carried by support platform  57 , which prevents an operator from operating the drive assembly  55  in the lifting direction that again could cause damage to lifting mast  51  and to a load carried by support platform  57 . 
     The present invention is described above with reference to a preferred embodiment. However, those skilled in the art will recognize that changes and modifications may be made in the described embodiment without departing from the nature and scope of the present invention. Various further changes and modifications to the embodiment herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof. 
     Having fully described the invention in such clear and concise terms as to enable those skilled in the art to understand and practice the same, the invention claimed is: