Abstract:
A low level scaffold with ball screw drive is a lightweight, mobile, compact, electrically activated, self-erecting, scissor-type lifting platform. The electronic system utilizes an electric motor in direct drive arrangement with a ball screw assembly to vary the platform height from a retracted position to extended position. Electric switches limit reverse direction between the retracted and extended positions to vary platform height anywhere between the minimum and maximum heights above ground level. The design allows for transportation through household doorways and provides anti-tilt arms with threaded level mounts for use on non-level surfaces. The scaffold provides homeowners and small commercial contractors with an apparatus to perform small interior and exterior projects at elevated heights.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority of Provisional Application No. 60/221,945, entitled LOW LEVEL SCAFFOLD filed on Jul. 31, 2000, and which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a scaffold having an electric drive for lifting a user, equipment, and materials from a ground level to an elevated working level within a contained area of height and width and to stabilize the scaffold on non-level ground, and mobility through interior passageways.  
           [0003]    The homeowner and small commercial contractor struggle with small interior and exterior projects that are at elevated heights. They primarily rely are stepladders, stools, and extension ladders for these projects. The user must constantly travel up and down these structures to retrieve tools and materials. The work area is limited to the reach to the user. This places the user in an unsafe situation that may result in a fall from an elevated height. As the user leans to extend his reach, the ladder or stool may become unstable and tilt or the user may loose his grip or balance and fall to the ground. Also, the user needs to constantly reposition the structure as the work progress. This is very inefficient wasting precise time. Stability of the structure is also an issue when working on unleveled surfaces. This is a particular problem when outdoors.  
           [0004]    Conventional aerial lifts are primarily designed for commercial and industrial users. The lifts initial purchase costs are high with significant reoccurring maintenance costs. The lifts employ hydraulics to elevate working platforms. The hydraulics requires significant maintenance and are constantly leaking making these machines unsuited for internal use for home or light industrial or small commercial operations. The relative size of the available machines also limits their use to external areas or internal spaces with wide doorways and high ceiling. Their use within a home or office is prohibited due to maneuverability through passageways and the leaking hydraulic fluid. Most conventional aerial lifts are powered by diesel engines, propane motors or large battery packs that also limits their usage within structures due to environment issues.  
           [0005]    In order to work safety at elevated heights within a house or office for the purpose of installing or fixing electric fixtures, painting walls or ceiling, or changing light bulbs, it is necessary to have an apparatus that is lightweight, low cost, portable and mobile, anti-tilt, sufficient load lifting capabilities, compact design in full retracted position, transportable through doorways, platform work area sufficient to reduce up and down trips by operator, level mount features allow placement on non-level surfaces, and a motorized direct drive elevating means to eliminate the hydraulics.  
           [0006]    Accordingly, several objects and advantages of my invention are to provide the consumer with a low cost, portable, mobile, multi-purpose scaffold for household use and light duty construction and maintenance.  
           [0007]    It is a further object of this invention to provide a scaffold that is of lightweight construction with anti-tilt features.  
           [0008]    It is a further object of this invention to provide a scaffold that has load-lifting capabilities up to 600 pounds.  
           [0009]    It is another object of this invention to provide a scaffold that is compact in full-retracted position.  
           [0010]    It is another object of this invention to provide a scaffold that is transportable through building doorways.  
           [0011]    It is yet another object of this invention to provide a scaffold with a platform work area that limits up and down trips by operator.  
           [0012]    It is a further object of this invention to a scaffold with level mount features that allow a scaffold to be placed on non-planar surfaces.  
           [0013]    It is a further object of this invention to provide a scaffold with a motor direct drive system that eliminates oil leakages associated with hydraulic systems.  
           [0014]    Still further objects and advantages will become apparent from a consideration of the ensuing description and accompanying drawings.  
         SUMMARY OF THE INVENTION  
         [0015]    The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.  
           [0016]    Briefly stated, the preferred embodiment introduces an improvement in scissor advancement mechanism that enables significant reduction in the size of a lifting scaffold for multipurpose use. The present invention provides a means for lifting construction material, tools and workman to working heights within a confined working area. For example, one embodiment of the present invention provides a lifting platform of conventional design wherein the platform is lifted from ground level and maintained in a substantially level height by a known scissor arrangement. The invention is sized to allow transportation through household doorways and other limiting structures. The scissor arrangement raises a load by mechanical lifting means driven by at least on electric motor means powered by AC or DC power. Preferably the mechanical lifting means includes at least one ball screw. The ball screw is connected to the scissor arrangement such that as the electric motor rotates the screw, the scissors open and the platform raises. The present invention employs the advantages of using a mechanical drive rather than hydraulic fluid to elevate the platform.  
           [0017]    An alternative embodiment includes electric micro switches provided in the assembly design to limit the extension and retraction position of the upper movable platform anywhere within a desired height range, preferably between 1 and 6.5 feet above surface level. These micro switches shut down electric power to the drive motor when mechanically activated.  
           [0018]    Another alternative embodiment includes casters for maneuverability and allows the operator to transport the apparatus from location to location in similar manner to a dolly.  
           [0019]    Yet another alternative embodiment includes stabilizing arms located on the stationary base to preclude the assembly from tipping over when the upper movable platform is fully extended. Leveling mounts located on the stabilizing arms allow the assembly to be mounted on non-level surfaces.  
           [0020]    For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is pictorial of the preferred embodiment;  
         [0022]    [0022]FIG. 2 is a side view of the scissor advancement mechanism attached to the stationary base and coupled to a scissor arm;  
         [0023]    [0023]FIG. 3 a  is a side view of the preferred embodiment in a fully extended position;  
         [0024]    [0024]FIG. 3 b  is a side view of the preferred embodiment in a fully retracted position;  
         [0025]    [0025]FIG. 4 is a schematic of the electrical circuitry;  
         [0026]    [0026]FIG. 5 is a cross-section of the ball screw mechanism;  
         [0027]    [0027]FIG. 6 a  is a top view of the scissor advancement mechanism in the fully extended position;  
         [0028]    [0028]FIG. 6 b  is a top view of the scissor advancement mechanism in the fully retracted position;  
         [0029]    [0029]FIG. 7 is a pictorial view of a lower rail;  
         [0030]    [0030]FIG. 8 is a front view of the dovetail rail configuration;  
         [0031]    [0031]FIG. 9 is a pictorial view of a stabilizing arm; and  
         [0032]    [0032]FIG. 10 is a pictorial view of a level mount. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    The preferred embodiment  10  (FIG. 1) includes an improved scissor advancement mechanism  12  (FIG. 2) that enables significant reduction in the size of a lifting scaffold for multipurpose use. Though the basic design of the stationary base  14 , the upper movable platform  16 , and the scissor assemblies  18  are standard and known to the art (also illustrated in FIGS. 3 a  and  3   b ), as discussed in detail in Provisional Application No. 60/221,945, entitled LOW LEVEL SCAFFOLD, the combination of the compact size and the improved scissor advancement mechanism  12  advances the art of lifting platforms. Each of the novel features will be discussed in detail below. Though a compact-sized lifting scaffold is illustrated, any size lifting scaffold is within the contemplation of the invention.  
         [0034]    As illustrated in FIGS. 1, 2,  3   a,  and  3   b,  the preferred embodiment  10  is comprised of a scissor advancement mechanism  12 , a stationary base  14 , an upper movable platform  16  disposed above the stationary base  14 , scissors lifting assemblies  18  having a lower  18   a  and upper portion  18   b  being interconnected between the stationary base  14  and the upper movable platform  16 , and a rail system  20 . The rail system  20  is fixedly connected to the scissor advancement mechanism  12 , in slidable contact with the stationary base  14  and upper movable platform  16 , and pivotally coupled to the scissors lifting assemblies  18 . The rail system (not shown) for the upper movable platform  16  is the same as for the stationary base  14 , and therefore the discussion of the rail system  20  adapted to the stationary base  14  is applicable to a rail system adapted to the upper movable platform  16 .  
         [0035]    The scissor advancement mechanism  12  is a combination of mechanical and electrical components, as illustrated in FIGS. 2 and 4. The scissor advancement mechanism  12  comprises a drive motor  22 , an externally threaded ball screw shaft  24  having a first  24   a  and a second  24   b  ends, an internally threaded nut  26 , two bearings  28   a,    28   b,  electric micro switches  30   a,    30   b  (FIG. 4 only), and a hand control  32 . The scissor advancement mechanism  12  (as shown in FIG. 2.) is fixedly mounted to the stationary base  14  with the drive motor  22  being mounted at the first end  14   a,  which opposes the scissors lifting assemblies  18  fixed pivotable attachment point at the second end  14   b.    
         [0036]    As illustrated in FIGS. 5, 6 a,  and  6   b,  the internally threaded nut  26  is threadably rotatable on the ballscrew shaft  24 , and is responsive to rotation of the ballscrew shaft  24  in the opposite first R′ and second R″ angular directions. The internally threaded nut  26  is movable in the opposite first L′ and second L″ linear directions between a retracted position, wherein the internally threaded nut  26  is located adjacent to the first end  24   a  of the ballscrew shaft  24 , and an extended position, wherein the internally threaded nut  26  is located adjacent to the second end  24   b  of the ballscrew shaft  24 .  
         [0037]    The wiring schematic shown in FIG. 4 illustrates the elevation control of the upper movable platform  16 . Electric micro switches  30   a,    30   b  are provided on the stationary base  14  and upper movable platform  16  at predetermined locations to limit the extension and retraction position of the upper movable platform  16  anywhere within a desirable height range, preferably between 1 and 6.5 feet above surface level. These micro switches  30   a,    30   b  shut down electric power to the drive motor  22  when mechanically activated. Electronic switch  30   a  shuts down power when the upper movable platform  16  descends below a predetermined point. Electronic switch  30   b  shuts down power when the upper movable platform  16  ascends above a predetermined point. A hand control  32  electrically connected to the drive motor  22  allows the operator to vary the height of the upper movable platform  16 . The drive motor  22  of this assembly is single-phase operating from 115 volts, 60-hertz or 230 volts, 50-hertz household AC electric power or DC electric power.  
         [0038]    The rail system  20  connects the major components of the preferred embodiment 10. As mentioned above, the rail system  20  is fixedly connected to the scissor advancement mechanism  12 , in slidable contact with the stationary base  14  and upper movable platform  16 , and pivotally coupled to the scissors assemblies  18 . As illustrated in FIG. 1, the rail system  20  includes two rails  34 , two rail guides  36 ,and a drive tube  37 . There are two rails  34  and two guide rails  36  for each the stationary base  14  and the upper movable platform  16 . The disclosure will be in terms of a rail system mounted on the stationary base  14 , however the structure for a rail system mounted to the upper movable platform  16  is exactly the same regarding the rails, the rail guides, and pivotal coupling with the scissor assemblies  18 .  
         [0039]    As illustrated in FIGS. 1, 6 a,    6   b,    7  and  8 , the rail  34  includes an opposite first  34   a  and second  34   b  ends, and a top surface  34   c,  and is mounted longitudinal on the stationary base  14  between the stationary base ends  14   a  and  14   b.  The positioning of the rail and number of rails are dependent on the load limits of the invention. The top surface  34   c  was made of or coated with low friction material for easy rail guide  36  sliding.  
         [0040]    The drive tube  37  is used to connect multiple rail guides  36  to the same drive motor  22 . As illustrated in FIGS. 6 a  and  6   b,  the preferred embodiment  10  uses one drive motor  22  working in cooperation with one ballscrew shaft  24 , one internally threaded nut  26 , and two rails  34 . Therefore, a coupling between the two rails  34  is required to translate both rail guides  36  along the rails  34  simultaneously. In cases where only one rail  34  is used, then there is no need for the drive tube  37 .  
         [0041]    As illustrated in FIGS. 7 and 8, the rail guide  36  includes a base plate  38 , a pair of pivot plates  40   a,    40   b,  and a coupling plate  42 . The base plate  38  includes a lower surface  38   a,  a top surface  38   b,  and opposite first end  38   c  and second end  38   d.  The second end  38   d  being attached at a first end  37   a  of the drive tube  37 . As illustrated in FIGS. 6 a  and  6   b,  the drive tube  37  is fixedly attached to the internally threaded nut  26  at a predetermined location such that when the internally threaded nut  26  undergoes movement in the opposite first L′ and second L″ linear directions the drive tube  37  applies equal force upon the rail guides  36 , whereby the rail guides  36  move along the rails  34  at the same velocity and distance.  
         [0042]    As illustrated in FIGS. 7 and 8, the rail guide  36  includes pivot holes  43   a,    43   b  sufficiently sized to mount a plurality of low friction material flanged sleeve bearings  45 . The scissor lift lower portion  18 a also includes a pivot hole  46  (not shown) sufficiently sized to mount a plurality of low friction material flanged sleeve bearings  45 . All flanged sleeve bearings  45  include a sleeve pivot hole  47  sufficiently sized such that a round shaft  44  freely rotates. Thereby, the guide rail  36  and the lower portions  18   a  of the scissor lift assembly are rotatably coupled by the round shaft  40  to operate the scissor lifting assembly  18  between the retracted (FIG. 3 b ) and expanded (FIG. 3 a ) conditions as the ballscrew shaft  24  is rotated in the opposite first R′ and second R″ angular directions.  
         [0043]    The rail guide base lower surface  38   a  is in slidable contact with the top surface  34   c  of the rail  34  as the rail guide  36  translates in the opposite first L′ and second L″ linear directions. The base plate  38  of the rail guide  36  further includes a channel  48  through the lower surface  38   a.  The channel  48  of the rail guide  36  and the rail  34  are a dovetail configuration (FIG. 8), both sufficiently sized such that the channel  48  of the rail guide  36  freely slides along the rail  34 , and to contain the rail guide  36  from extending upwardly under loading conditions as the rail guide  36  translates in the opposite first L′ and second L″ linear directions.  
         [0044]    The rail system  49  (partial shown in FIG. 1) of the upper movable platform  16  is identical to the rail system  20  described above. The rail guide  50  of the upper movable platform  16  translates along the rail (not shown) attached to the upper movable platform  16  as the upper portion  18   b  of the scissor assemblies  18  applies a force to the rail guides  50  similar to the force applied by the drive tube  37  upon the rail guides  36  on the stationary base  14 .  
       MODE OF OPERATION  
       [0045]    The operator of the present invention positions the invention in a work area, loads the material and tools on to the upper movable platform  16 , steps on to the upper movable platform  16 , and turns on the motor. The operator pushes the up button to engage the drive motor  22  with the ballscrew shaft  24 . The ballscrew shaft  24  undergoes rotation R′ in a first angular direction. The internally threaded nut  26  undergoes translation L′ in a first linear direction so as to cause movement of the scissors assemblies  18  vertically toward the extended condition and thereby movement of the upper movable platform toward the raised position (FIG. 3 a ). When the operator reaches the desired height, the operator releases the up button to disengage the ballscrew shaft  24  from the drive motor  22 .  
         [0046]    Upon completion of the work, the operator pushes the down button and the upper movable platform  16  descends. The ballscrew shaft  24  undergoes rotation R″ in a second angular direction opposite to the first angular direction, and the internally threaded nut  26  undergoes translation L″ in a second linear direction opposite to the first linear direction so as to cause movement of the scissor assemblies  18  vertically toward the retracted condition and thereby movement of the upper movable platform  16  toward the lowered position (FIG. 3 b ). Once the upper movable platform  16  lowers to the desire ascent height, the operator releases the down button.  
         [0047]    Preferably, the scissor advancement mechanism  12  also includes electronic switches  30   a,    30   b  (as mentioned above), which effectively stop the upper movable platform  16  at maximum ascent and descent heights.  
         [0048]    An alternative embodiment, illustrated in FIG. 1, includes stabilizing arms  54  connected to predetermined locations of the stationary base  14 . As illustrated in FIG. 9, the stabilizing arm  54  includes a pivot arm  56 , having opposite first  56   a  and second  56   b  ends, and a mounting arm  57 . The mounting arm  57  being fixedly attached to the stationary base  14 . The pivot arm first end  56   a  is pivotally coupled to the mounting arm  57  for retraction when the apparatus is not in use and extension when the apparatus is in use. The second end  56   b  includes a threaded hole  56   t  to receive an externally threaded swivel level mount  58 , whereby the stabilizing arms  54  are variably extendible for use in confined areas or for adjusting for loads that affect the center of gravity of the apparatus. The externally threaded swivel level mount  58  is threadably rotatable into the threaded hole  56   t  of the pivot arm  56 , whereby the swivel level mount  58  is threaded into the threaded hole  56 T of the pivot arm  56  to a height sufficient to adapt the apparatus for use on non-level surfaces providing a stable surface for the apparatus to operate.  
         [0049]    In another alternative embodiment, the stationary base  14  further includes at least one caster  60  (FIG. 1), whereby the caster adapts the apparatus for easy movement, transportation, repositioning, or realignment by one individual.  
         [0050]    In yet another alternative embodiment, the stationary base  14  further includes a plurality of externally threaded swivel level mounts  62  (FIG. 10) being connected to predetermined locations of the stationary base  14 . The threaded swivel level mount  62  is threadably rotatable into the threaded hole  66 t of a mount plate  66 , whereby the swivel level mount  62  is threaded into the threaded hole  66 T of the mount plate  66  to a height sufficient to adapt the apparatus for use on non-level surfaces providing a stable surface for the apparatus to operate. The mount plate  66  is fixedly attached to the stationary base  14 .  
         [0051]    Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims.