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BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates generally to spa cover assemblies. More particularly, the invention relates to moveable spa cover assemblies. Specifically, the invention relates to a vertically adjustable spa cover assemblies. 
     2. Background Information 
     Cover assemblies for spas, also known as hot tubs, and for swimming pools have been known for quite some time. There are a variety of configurations, some of which move in various ways. However, there is a need for a spa cover assembly which is vertically adjustable and which can be either built into a spa or added as a retrofit cover assembly. Such movable cover assemblies allow the user to selectively use the, cover assembly based on weather conditions. 
     The prior art includes a dome-shaped cover having a semi-dome-shaped portion that rotates about a central point above the spa to open and close the cover (U.S. Pat. No. 4,246,663 granted to Aragona et al.). U.S. Pat. No. 5,148,646 granted to Lutostanski discloses a convertible enclosure for hot tubs and the like, which includes a tubular frame with sliding cross pieces to which a cover is attached to encompass one side and the top of the space over the hot tub with one side remaining open. U.S. Pat. No. 5,680,893 granted to Neer discloses a retractable decorative screen to provide privacy around swimming pools and the like which slides back and forth horizontally on an overhead track, or on a cable or rope. U.S. Pat. No. 6,079,059 granted to Girerd discloses a movable covering device or roof which moves on hinged structural members from a position above a swimming pool to a position above an adjacent terrace. U.S. Pat. No. 6,212,702 granted to Sitzmann discloses a rectangular spa cover wherein two poles are hingedly connected to adjacent corners of the cover and hingedly connected to the spa deck to facilitate lifting the cover from a position on the ground beside the spa to a position over the spa, with two other poles then being respectively connected to the other two corners of the cover and the deck. U.S. Pat. No. 6,374,433 granted to Gray discloses a rigid house-like hot tub cover which moves horizontally along a deck on rollers or the like from a position over the hot tub to a position adjacent the hot tub. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides one embodiment wherein a vertically adjustable spa cover assembly has lifts that move a cover, a screen or a combination thereof between a raised position and a lowered position. 
     In one embodiment, corner lifts are used to raise and lower the insulated cover of the spa. A screen may be connected to the cover. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first embodiment of the spa cover assembly of the present invention in the raised position; 
     FIG. 2 is a perspective view of the first embodiment of the spa cover assembly in the lowered position; 
     FIG. 3 is a schematic view of the first embodiment of the spa cover assembly showing the motor, sprockets and chain. 
     FIG. 4 is a schematic view of a second embodiment of the present invention; 
     FIG. 5 is a fragmentary sectional view of the spa cover assembly in the lowered position showing one lift in its lowered position; 
     FIG. 6 is a fragmentary sectional view of the spa cover assembly in an intermediate position of being raised; 
     FIG. 7 is an enlarged view of the encircled portion of FIG.  6 . 
     FIG. 8 is a fragmentary sectional view of the spa cover assembly in a further stage of being raised showing the medial section in a fully extended position; 
     FIG. 9 is a fragmentary sectional view of the spa cover assembly in a further stage of being raised; 
     FIG. 10 is a fragmentary sectional view of the spa cover assembly in the raised position; 
     FIG. 11 is an enlarged view of the upper encircled portion of FIG.  10 . 
     FIG. 12 is an enlarged view of the lower encircled portion of FIG.  10 . 
     FIG. 13 is a schematic view of a third embodiment of the present invention; 
     FIG. 14 is a fragmentary sectional view of the third embodiment of the present invention in the lowered position; 
     FIG. 15 is a fragmentary sectional view of the third embodiment of the present invention in the raised position; 
     FIG. 16 is a perspective view of a fourth embodiment of the present invention in the raised position; 
     FIG. 16A is a perspective view of the fourth embodiment of the spa cover assembly in the lowered position; 
     FIG. 17 is a fragmentary perspective view of a fifth embodiment of the present invention in the raised position showing a rotated position of the cover in phantom; 
     FIG. 18 is a perspective view of a sixth embodiment of the present invention in the raised position; and 
     FIG. 19 is a fragmentary sectional view of the spa cover assembly shown in FIG.  18 . 
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The first embodiment of the spa cover assembly of the present invention is indicated generally at  10  in FIGS. 1-3 and  5 - 12 . Cover assembly  10  includes cover  12  and lifts  14 . Lifts  14  are configured to move cover  12  vertically between a raised position (FIG. 1) and a lowered position (FIG. 2) above a spa  16  having an upper surface  18 . 
     Cover  12  sits atop four lifts  14  and may be attached thereto, if desired, by any suitable means. For example, cover  12  may be attached to lifts  14  with bolts, pins, screws, snap fits, etc. Preferably, any attachment used is removable both for safety and convenience. Cover  12  may also be attached to, for example, two lifts  14  by hinges (not shown) as a safety feature. Cover  12  may include thermal insulation (not shown) and may be made of a wide variety of materials, such as netting, or materials which are wind-proof, water-proof, transparent, translucent, opaque, and so forth. When cover  12  includes insulation, cover  12  is used to keep the water in spa  16  warm when spa  16  is not in use. 
     Lifts  14  may be made of a plastic material with appropriate strength which can withstand a wide range of temperature changes suitable to various weather conditions. They may be manufactured of nylon or reinforced nylon. Other materials that may be injection molded may be used. Various polymers and thermoplastics, or other suitable materials may also be used. 
     Each lift  14  (FIGS. 5-12) is housed at least partially in a sleeve  20  having a top  21  as each lift  14  moves between the lowered position (FIG. 5) and the raised position (FIG.  10 ). In the lowered position, lifts  14  are flush with or below upper surface  18  of spa  16 . 
     Each lift  14  (shown in FIG. 10) includes a plurality of threaded sections each of which threadedly engages one of the other threaded sections. All threads used in lifts  14  have the same pitch. Ball screws may also be used, wherein there is a ball-bearing-to-thread engagement instead of a thread-to-thread engagement between the various sections of each lift  14 . Specifically, lift  14  includes a lower section which is a threaded rod  22  sitting atop support member  23  and having a lower end  24  and an upper end  26 . A lower stop  28  is connected to lower end  24 , an upper stop  30  is connected to upper end  26 , and a sprocket  32  (FIG. 3) is connected to lower stop  28 . A tapered tip  33  is connected to upper stop  30 . Each threaded rod  22  extends upwardly at slightly varying heights, as explained below. 
     Lift  14  also includes a medial section which is a hollow pipe  34  having a lower end  36  and an upper end  38 , each end being internally threaded. Lower end  36  threadedly engages threaded rod  22 . Lift  14  further includes an upper section which is an externally threaded hollow tube  40  having a bottom end  42  and a top end  44 . A bottom stop  46  is connected to bottom end  42  and a top stop  48  is connected to top end  44 . Hollow tube  40  threadedly engages upper end  38  of hollow pipe  34 . Cover  12  sits atop stop  48 . 
     In the lowered position (FIG.  5 ), rod  22  is situated substantially within pipe  34 , which is in turn situated substantially within tube  40 , and all three sections are partially housed within sleeve  20 . In the raised position (FIG.  10 ), rod  22  is situated as in the lowered position with tapered tip  33 , with upper stop pipe  30  and a upper end  26  being within pipe  34 . In the raised position, bottom stop  46  and bottom end  42  of tube  40  are within pipe  34 . 
     In the first embodiment of the invention, sprockets  32  (FIG. 3) engage a chain  50 , which extends around the four sprockets  32  and engages a sprocket  52  attached to an electric motor  54 . Chain  50  further engages tensioners  56 . Motor  54  is wired to control buttons  58 , which in turn is wired to attach to a source of electricity (not shown). Instead of a chain  50 , a cable (not shown) held in tension may be used to engage rods  22  via reinforced channels (not shown) therein or pulleys (not shown) thereabout or the like instead of sprockets  32 . In addition, a plurality of individual motors (not shown) may be used to raise and lower each respective lift  14 , directly or indirectly, each motor being timed together to work simultaneously. 
     Cover assembly  10  is configured to move between a raised position (FIG. 1) and a lowered position (FIG.  2 ). To raise assembly  10 , a user pushes one of buttons  58  (FIG. 3) to supply electric power to operate motor  54  to rotate sprocket  52 , which engages and drives chain  50 , which in turn engages and rotates sprockets  32  and consequently threaded rod  22 . Alternately, a cable (not shown) may be used to engage and rotate rod  22  as described above. The rotation of rod  22  causes it to unthread from threaded lower end  36  of hollow pipe  34 , which causes pipe  34  and tube  40  to move vertically upward and begin raising assembly  10  (FIG.  6 ). Rod  22  unthreads from pipe  34  until upper stop  30  engages lower end  36  of pipe  34 , thus preventing further unthreading and upward movement of pipe  34  (FIG.  8 ). Stop  30  also prevents the disengagement of pipe  34  from rod  22 . As stop  30  engages lower end  36  of pipe  34 , pipe  34  also begins to rotate along with rod  22 . Because each rod  22  is a slightly different height, the engagement of each stop  30  with each respective lower end  36  is staggered a short time apart to ease torque on motor  54  that would occur if all rods  22  were the same height and all stops  30  thus engaged respective lower ends  36  simultaneously. The rotation of each pipe  34  along with rod  22  causes tube  40  to unthread from upper end  38  of pipe  34 , which causes tube  40  to move vertically upward and continue the raising of assembly  10  (FIG.  9 ). Tube  40  unthreads from pipe  34  until bottom stop  46  engages upper end  38  of pipe  34 , thus preventing further unthreading and upward movement of tube  40  (FIG.  10 ). Because all threads in lift  14  have the same pitch, assembly  10  is raised at a constant rate throughout the raising process. Lifts  14  may, however, include a tube  40  and an upper end  38  each having threads with a different pitch than those of rod  22  and lower end  36 , so that the rate of raising would change when tube  40  began to unthread from upper end  38 . 
     To lower cover assembly  10 , the user pushes the other of buttons  58 , which causes the motor to rotate in a direction opposite that for raising assembly  10 . Thus, all moving parts move or rotate in opposite directions and the process is essentially reversed. As assembly  10  is lowered, tapered tip  33  serves a self-centering function to ensure that rod  22  will be smoothly inserted into tube  40 . In lowering assembly  10 , top stop  48  engages upper end  38  of pipe  34  to prevent further threading and downward movement of tube  40 . Likewise, lower stop  28  of rod  22  engages lower end  36  of pipe  34  to prevent further threading and downward movement of rod  22 . 
     As noted above, lifts  14  in the lowered position are flush with or below upper surface  18  of spa  16 . Thus, cover  12  may be removed and lifts  14  lowered to eliminate unsafe protrusions extending upwardly from spa  16 . Sleeve  16  may be covered or sealed against the entrance of water if desired. 
     A second embodiment of the present invention is shown in FIG.  4  and includes modified cover assembly  110 . Assembly  110  is similar to assembly  10  except that sprocket  152  engages a hand crank  154  (FIG. 4) as an alternate power source instead of motor  54  of assembly  10 . 
     A third embodiment of the present invention is shown in FIGS. 13-15 and includes modified cover assembly  210 . Assembly  210  is similar to assembly  10  except that lifts  214  are different and that lifts  214  are operated by system  216 , which is a pneumatic or hydraulic system. System  216  may include a source of power  218 , a valve  220 , a divider  222 , and a plurality of lines  224 , all respectively connected to one another. Lines  224  are connected to lifts  214 . Source of power  218  is either pneumatic or hydraulic. Each lift  214  may include three telescoping members  226 . Each lift  214  may also include a safety latch (not shown) to prevent assembly from falling in case system  216  fails. The safety latch may be, for example, a ratchet system attached to lift  214  or a solenoid valve located near lift  214 . 
     Source of power  218  pressurizes air in the pneumatic system or hydraulic fluid in the hydraulic system. The source of power for the pneumatic system may be the compressor that is built in to many spas or a separate source. Valve  220  allows air or hydraulic fluid to flow in alternating directions to respectively raise and lower lifts  214 . Divider  222  allows the air or fluid to branch so as to flow through lines  224  and vice versa. Lines  224  deliver the air or fluid to lifts  214  to raise and lower them. Telescoping members  226  are thus raised and lowered by a typical pneumatic or hydraulic system. 
     A fourth embodiment of the present invention is shown in FIGS. 16 and 16A and includes modified cover assembly  310 . Assembly  310  is similar to assembly  10  except that assembly  310  includes screen  311 , which is removably attached to cover  312  by a plurality of snaps  320 , velcro or other suitable fasteners, and may be attached to itself as well with fasteners. Screen  311  may also be attached to lifts  14  instead of cover  312 , and thus screen  311  may be used without cover  12  if desired. Screen  311  includes a door  322 , which may utilize a zipper or other suitable means for opening and closing. Screen  311  is a single piece of material surrounding the perimeter defined by lifts  14  in the raised position (FIG. 16) and surrounds spa  16  in the lowered position (FIG.  16 A). Screen  311  may be provided in sections. Screen  311  may be netting, such as mosquito netting, or may be wind-proof, water-proof, insulated, transparent, translucent, opaque, or any variety of combinations thereof, or any other appropriate material. 
     Screen  311  adds the convenience of creating a wide variety of settings, to include netting to keep bugs out, or material to block wind and rain or provide shade in varying degrees. Amongst other things, it may also be used to add thermal insulation, privacy and for decorative purposes. 
     A fifth embodiment of the present invention is shown in FIG.  17  and includes modified cover assembly  410 . Assembly  410  is similar to assembly  10  except that assembly  410  includes a modified cover  412 , only one lift  414  and a telescoping guide  416 . Guide  416  extends from cover  412  downward into spa  16  parallel to lift  414 . Guide  416  is fixedly attached to spa  16  and is removably attached to cover  412 . Cover  412  includes an attachment housing  418  attached to lift  414  and support arms  420  extending from housing  418 . The power source (not shown) to rotate lift  414  may be as described above in relation to assemblies  10  and  110 , with modifications as desired for a single lift  414 , or as described below in relation to assembly  510 . Cover  412  may also be hingedly attached to lift  414  as a safety precaution to allow the user to lift cover  412  in case of emergency, for example, where lift  414  became stuck in the lowered position due to loss of power to lift  414 . 
     Cover assembly  410  is configured to allow cover  412  to rotate about lift  414  when in the raised position, allowing the user to alter shading on or adjacent the spa or alter the view from the spa without removing the cover. Guide  416  telescopes out and in to prevent said rotation while cover  412  is being raised or lowered, respectively. Guide  416  does not aid in lifting. When assembly  410  is in the raised position, guide  416  may detached from cover  412  to allow cover  412  to rotate as noted above. Housing  418  provides a structure for mounting cover  412  on lift  414 , such as with a bracket (not shown). Arms  420  provide support for cover  412  to allow assembly  410  to function with only a single lift  414 . 
     A sixth embodiment of the present invention is shown in FIGS. 18-19 and includes modified cover assembly  510 . Assembly  510  is similar to assembly  410  (fifth embodiment) except that assembly  510  includes a modified lift  514 , a lift housing  516 , a modified attachment housing  518  connected to a bracket  519 , a modified motor  520  and a screen  522 , but does not include a guide ( 416 ), although a guide could be included. Lift  514  includes threaded rod  524  having a lower end  526  and a beveled gear  528  connected to rod  524  adjacent lower end  526 . Motor  520  is connected to beveled gear  530  which engages gear  528 . Spa  16  defines a hole  532  adjacent motor  520 . 
     Assembly  510  is configured as a retrofit assembly which can be attached to spa  16 . Motor  520  is inserted into hole  532  cut in spa  16  to protect motor  520  from weather. Lift housing  516  is attached to spa  16  to provide support for lift  514 . Housing  516  also functions to guard motor  520  and lift  514  from weather and shields the user from moving parts. Housing  518  provides a structure for externally mounting cover  512  on lift  514  with bracket  519 . Screen  522  surrounds spa  16  in the lowered position and as assembly  510  is being raised, and thus prevents the rotation of assembly  510  about lift  514  until screen  522  is above spa  16 . While screen  522  prevents this rotation, a guide such as guide  416  (FIG. 17) may be included for this purpose, especially if the user wishes to use assembly  510  without screen  522 . Motor  520  is adapted to bevel gear  530 , which engages gear  528  to rotate lift  514  to raise and lower assembly  510 . Other power sources may be used and the means of engaging and rotating rod  522  may vary. 
     In any of the embodiments involving lifts with threaded sections, the means of engaging the lower section of the lift could be a gear, a sprocket, a smooth or textured surface or other suitable configuration. One alternate example is a motor adapted with an elastomeric wheel which could engage and rotate the rod. Further, a variety of other means of lifting assembly  10  may be used. For example, assembly  10  may be lifted with levers in various arrangements, such as a scissors-type lift or a lift using levers and cables. 
     In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries and principles of the invention, the manner in which the vertically adjustable spa cover assembly is constructed and used, the characteristics of the construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations are set forth in the appended claims.

Summary:
A vertically adjustable spa cover assembly includes a cover movable above a spa between a raised position and a lowered position, the raised position being vertically above the lowered position. Lifts are used to raise and lower the cover. The cover assembly may also include a screen that surrounds the area between the cover and the spa. The lifts are threaded sections including rods and pipes which engage one another and move up and down as one or more of these threaded sections are rotated by a power source such as a motor or hand crank. The power source may engage the threaded sections through gears or sprockets, or less directly via a system of sprockets and a chain which drives the sprockets and the threaded sections in turn. Alternately, the lifts may be telescoping members pneumatically or hydraulically powered. The cover assembly may be built into a spa unit or added as a retrofit component.