Abstract:
A multi-wheeled base for a mobile cart includes one or more swiveling, optionally locking, caster wheels and one or more non-swiveling traction wheels to improve the maneuverability of the cart by making it easier to steer and stop. The traction wheels may be manually-engaged traction wheels, which may be operated by a cam and lever. The traction wheels may also be automatically-engaged traction wheels operated by a motor and a threaded shaft, and activated by a motion-sensitive sensor or by an on/off electrical switch or button. The traction wheels are preferably in contact with the floor when the mobile cart is moving, and raised above the surface of the floor when the cart is stationary.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/308,965, entitled “MOBILE CART BASE WITH TRACTION WHEEL,” filed on Feb. 28, 2010, and is a continuation-in-part and claims priority to co-pending U.S. patent application Ser. No. 12/418,338, entitled “MOBILE CART,” filed on Apr. 3, 2009, which itself claims priority to U.S. Provisional Patent Application Ser. No. 61/074,170, entitled “BEDSIDE MEDICATION DELIVERY CART,” filed on Jun. 20, 2008. The entire contents of all three priority applications are expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of carts, and particularly to mobile carts with multi-wheeled bases. 
     BACKGROUND OF THE INVENTION 
     Mobile carts are employed in many industries, and may be used to carry a computer, monitor, display, or other electronic equipment; to provide a work surface, such as for a computer keyboard and mouse; and/or to provide portable storage, such as a tray or compartment. The overall weight of some mobile carts, particularly those equipped with electronic equipment and power supplies, may be an ergonomic issue. With an average weight exceeding 100 pounds, pushing a mobile cart can be tiring and cumbersome, especially for smaller users. 
     In the past, mobile carts have been equipped with four swivel casters or wheels, which permit the user to maneuver the cart around corners, or push it out of the way if necessary, but makes the cart difficult to steer. In particular, the momentum of the cart may be a problem if the cart is moved quickly, as the cart may become difficult to stop or turn. In addition, the carts are difficult to push in a straight line, as the four swivel casters may cause the cart to move slightly from side to side as it pushed, especially if the floors are uneven. 
     The maneuverability of a mobile cart can be improved by making two of the four casters ridged or non-swiveling. In this configuration, the mobile cart operates much like a shopping cart, and the user steers the cart by controlling the front end. This is not ideal, however, because it is still difficult to turn tight corners, and nearly impossible to pivot in place. 
     There is a need in the art, then, for a mobile cart that is easy to maneuver; a cart that can turn effortlessly and quickly, without a concern that the momentum of the cart will lead the cart astray. In addition, there is a need for a mobile cart that will move in a straight line when pushed, and will self-adjust so that the wheels stay in contact with the floor, either automatically, in response to the movement of the cart, or manually. 
     SUMMARY OF THE INVENTION 
     The invention provides a multi-wheeled base for a mobile cart. The base may include one or more swiveling, optionally locking, caster wheels and one or more non-swiveling traction wheels to improve the maneuverability of the cart by making it easier to steer and stop. The traction wheels may be manually-engaged traction wheels, which in one non-limiting example may be operated by a cam and lever. The traction wheels may also be automatically-engaged traction wheels operated by a motor and a threaded shaft, activated by a motion-sensitive sensor or by an on/off electrical switch or button. 
     The multi-wheeled base may comprise a base frame that is generally rectangular, and may include four protruding legs, one leg extending from and proximate each corner of the base frame. One swiveling caster wheel may be mounted to each of the protruding legs. If the base frame does not include the protruding legs, the swiveling caster wheels may be mounted to the base frame at the corners of the base frame. 
     The base frame is preferably configured to accommodate one or more optional battery cell housings and battery cells, in which case an electrical interconnect assembly is used to connect the battery cells and provide electrical connections for the mobile cart, including the electrical connections needed to power the automatically-engaged traction wheel. 
     One non-limiting embodiment of the manually-engaged traction wheel includes a traction wheel housing and a cam and lever wheel-positioning assembly. The traction wheel housing includes a wheel assembly sandwiched between two assembly plates, such that the wheel assembly may move up and down a short distance relative to the assembly plates. The up and down movement of the wheel assembly is controlled by the cam and lever assembly, and is guided and limited by elongated slots defined in the assembly plates. When the lever is in a first position, the cam and lever assembly is engaged, the wheel assembly is lowered, and the wheel of the wheel assembly touches the floor or ground. When the lever is moved up or down ninety-degrees from the first position, the cam and lever assembly is disengaged, the wheel assembly is raised, and the wheel is lifted off the floor or ground. 
     In a non-limiting embodiment, the automatically-engaged traction wheel includes a traction wheel housing and a motor and threaded shaft wheel-positioning assembly. The traction wheel housing includes a wheel assembly sandwiched between two assembly plates, such that the wheel assembly may move up and down a short distance relative to the assembly plates. The up and down movement of the wheel assembly is controlled by the motor and shaft assembly, and is guided and limited by elongated slots defined in the assembly plates. A Hall effect sensor is used to detect an “on/off” signal from a magnet embedded in the rotating wheel. As long as the Hall effect sensor detects the “on/off” signal from the magnet, the motor and the threaded shaft turn such that the wheel assembly is lowered, and the wheel touches the floor or the ground. When the Hall effect sensor stops receiving the “on/off” signal from the magnet, because the wheel is no longer rotating, the motor and the threaded shaft turn such that the wheel assembly is lifted, and the wheel is lifted off the floor or ground. 
     In an embodiment, mobile cart base comprises a base frame having a generally rectangular shape and a front frame member, a rear frame member, two opposing side members, and a center frame member coupled to the front frame member and the rear frame member, where the center frame member is generally parallel to the opposing side members and generally perpendicular to the front frame member and the rear frame member; four swiveling wheels mounted to the base frame proximate each of the four corners of the base frame; and a non-swiveling traction wheel mounted to the center frame member, where the traction wheel comprises a cam and lever assembly that is adapted to raise and lower the traction wheel relative to the base frame. 
     In another embodiment, a mobile cart base comprises a base frame having a generally rectangular shape and a front frame member, a rear frame member, two opposing side members, and a center frame member coupled to the front frame member and the rear frame member, where the center frame member is generally parallel to the opposing side members and generally perpendicular to the front frame member and the rear frame member; four swiveling wheels mounted to the base frame proximate each of the four corners of the base frame; and a non-swiveling traction wheel mounted to the center frame member, where the traction wheel comprises a motor and threaded spindle assembly that is adapted to raise and lower the traction wheel relative to the base frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a perspective view of a preferred embodiment of a rolling base section of a mobile cart base; 
         FIG. 2  is a perspective view of the rolling base section of  FIG. 1 , showing the addition of front and rear cover members; 
         FIG. 3  is a perspective view of the rolling base section of  FIG. 2 , showing the addition of corner cover members; 
         FIG. 4  is a perspective view of the rolling base section of  FIG. 3 , showing the addition of a manually-engaged traction wheel; 
         FIG. 5  is a perspective view of the rolling base section of  FIG. 4 , showing the addition of battery cell compartments; 
         FIG. 6  is a perspective view of the rolling base section of  FIG. 5 , showing the addition of a spring assembly and an electrical interconnect assembly; 
         FIG. 7  is a perspective view of the rolling base section of  FIG. 6 , showing the addition of battery cells; 
         FIG. 8A  is a perspective view of the rolling base section of  FIG. 7 , showing the addition of a top cover member; 
         FIG. 8B  is a perspective view of a mobile cart; 
         FIG. 9A  is perspective view of a wheel assembly for a manually-engaged traction wheel; 
         FIG. 9B  is an exploded view of the components of the wheel assembly of  FIG. 9A ; 
         FIG. 9C  is a perspective view of a traction wheel housing for a manually-engaged traction wheel; 
         FIG. 9D  is an exploded view of the components of the traction wheel housing of  FIG. 9C ; 
         FIG. 9E  is a side view of a manually-engaged traction wheel; 
         FIG. 9F  is a front view of the manually-engaged traction wheel of  FIG. 9E ; 
         FIG. 9G  is an exploded view of the components of a cam and lever assembly of the manually-engaged traction wheel of  FIG. 9E ; 
         FIG. 9H  is an exploded view of the components of the manually-engaged traction wheel of  FIG. 9E ; 
         FIG. 10A  is a perspective view of a wheel assembly for an automatically-engaged traction wheel; 
         FIG. 10B  is an exploded view of the components of the wheel assembly of  FIG. 10A ; 
         FIG. 10C  is a front view of a motor and shaft assembly for an automatically-engaged traction wheel; 
         FIG. 10D  is a side view of the motor and shaft assembly of  FIG. 10C ; 
         FIG. 10E  is an exploded view of the components of the motor and shaft assembly of  FIG. 10C ; 
         FIG. 10F  is an exploded view of the motor electrical assembly of the motor and shaft assembly of  FIG. 10E ; 
         FIG. 10G  is a perspective view of an automatically-engaged traction wheel; 
         FIG. 10H  is an exploded view of the components of the automatically-engaged traction wheel of  FIG. 10G ; and 
         FIG. 10I  is an exploded view of a traction wheel housing for an automatically-engaged traction wheel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I. Mobile Cart Base 
     With reference to  FIGS. 1 through 8 , in a preferred embodiment, mobile cart base  800  comprises a rolling base section  100  that includes a generally rectangular base frame  105  and four omni-directional, optionally locking swiveling casters or wheels  110 . In alternate embodiments, mobile cart base  800  may include a generally elliptical base frame, or a base frame comprising three, four or more sides, and may have two, three or more swiveling wheels. 
     As shown in  FIG. 1 , base frame  105  comprises a front frame member  106 , a rear frame member  107 , two opposing side frame members, left side member  108  and right side member  109 , and center frame member  140 . In a preferred embodiment, base frame  105  includes four protruding legs  120 , one protruding leg located proximate each corner of the base frame  105 . Base frame  105  is preferably constructed of metal, although other materials, suitable for accommodating the weight of the mobile cart, are within the scope of the invention. One swiveling caster or wheel  110  is coupled to each protruding leg  120  with washers  131  and nut  133 , although other types of connectors or fasteners known in the art may be used. In alternate embodiments, protruding legs  120  are optional, and one swiveling caster or wheel  110  may be coupled directly to each of the corners of base frame  105 , or proximate the corners of base frame  105 . 
     As shown in  FIGS. 2 and 3 , front cover member  220  is mounted to base frame  105  proximate the center of front frame member  106 , and rear cover member  210  is mounted to base frame  105  proximate the center of rear frame member  107  with screws  230 , or other types of connectors or fasteners. In a preferred embodiment, front cover member  220  and rear cover member  210  are made of plastic. 
     As shown in  FIGS. 3 and 4 , each of the corner cover members  310 ,  320 ,  330  and  340  is mounted to base frame  105  proximate each of the corners of base frame  105  with screws  350  or other types of known fasteners or connectors, so as to cover the tops of the protruding legs  120 . Once mounted to base frame  105 , and as shown in  FIG. 4 , corner cover members  330  and  340  and front cover member  220  are adapted and configured to cover substantially the entire top of front frame member  106 . Similarly, corner cover members  310  and  320  and rear cover member  210  are adapted and configured to cover substantially the entire top of rear frame member  107  once mounted to base frame  105 . Corner cover members  310 ,  320 ,  330  and  240  are preferably made of plastic. 
     With reference to  FIG. 4 , and as described in detail below, manually-engaged traction wheel  990  is mounted to center frame member  140  with screws  410  or other known forms of connectors or fasteners. 
     As shown in  FIG. 5 , optional battery cell compartments  510  and  520  are generally cube-shaped with an open top and a closed bottom, and are adapted to house the battery cells that provide power to the electrical components housed on the mobile cart. Battery cell compartment  510  comprises left and right top flanges,  515  and  516  respectively. Left top flange  515  is adapted to rest on top of at least a portion of the top of left frame member  108 , and right top flange  516  is adapted to rest on top of at least a portion of the top of the center frame member  140 . Similarly, battery cell  520  comprises left and right top flanges  526  and  527 , respectively. Left top flange  526  is adapted to rest on top of at least a portion of the top of the center frame member  140 . Right top flange  527  is adapted to rest on top of at least a portion of the top of right frame member  109 . 
       FIG. 6  shows the addition of spring assembly  610  and electrical interconnect assembly  620  to base frame  105 . Spring assembly  610  is used to exert a slight downward pressure on the wheel assembly  940  of manually-engaged traction wheel  990 , as described in detail below. Spring assembly  610  acts as a shock absorber, allowing wheel assembly  940  to give and still remain in contact with the floor. Electrical interconnect assembly  620  connects the battery cells  710  and  720 , which are shown in  FIG. 7  and described below. 
     In a preferred embodiment, spring assembly  610  comprises a bushing  611 , a spring  612 , a retainer  613  and one more screws or fasteners  614  to couple retainer  613  to center frame member  140 . Spring  612  is preferably a compression spring. 
     In a preferred embodiment, electrical interconnect assembly  620  comprises interconnect board  621 , interconnect board housing  622 , screws  623  to couple interconnect board  621  to interconnect board housing  622 , and screws or fasteners  624  to couple interconnect board housing  622  to center frame member  140 . In alternate embodiments, interconnect board  621  includes a connector (not shown) that is used to power an automatically-engaged traction wheel  1010 , described in detail below. 
     As shown in  FIG. 7 , optional battery cells  710  and  720  are housed in optional battery cell compartments  510  and  520 , respectively, and coupled to base frame  105  with screws or fasteners  730 . 
       FIG. 8A  shows the addition of top cover member  810 , which completes a preferred embodiment of the mobile cart base  800 . Top cover member  810  is preferably made of plastic. 
     In an alternate embodiment, the base frame  105  may not include center frame member  140 , battery cell compartments  510  and  520 , and/or battery cells  710  and  720 , and the manually-engaged traction wheel  990  may be mounted to either or both of the left and right frame members  108  and  109 . 
     In one non-limiting embodiment, mobile cart base  800  may be used as the rolling base section for a mobile cart, such as mobile cart  8200  shown in  FIG. 8B . Mobile cart  8200  may comprise a mobile cart base  800 , upper working section  8210 , and intermediate section  8230 . Intermediate section  8230  may comprise a length-adjustable upwardly-extending post  8232 , which allows the height of upper working section  8210  to be adjusted. Upper working section  8210  may include a keyboard support  8271  adapted to carry keyboard  8270 , and one or two retractable mouse trays  8272 . Mobile cart  8200  may also carry a computer (not shown), such as by a bracket coupled to upper working section  8210 . Upper working section  8210  may also carry a computer monitor  8260  and a storage compartment  8250 . Mobile cart  8200  may also include a front projecting handle  8850  and a rear projecting handle  8860  to allow a user to roll the mobile cart. 
     II. Manually-Engaged Traction Wheel 
     The details of manually-engaged traction wheel  990 , shown previously in  FIGS. 4 through 7  and  8 A, are shown in  FIGS. 9A through 9H . With reference to  FIGS. 9E ,  9 F, and  9 H, manually-engaged traction wheel  990  comprises traction wheel housing  910 , cam and lever wheel-positioning assembly  920 , and cover plate  930 . As shown in  FIG. 9G , wheel-positioning assembly  920  comprises a cam  922 , block  925 , and a lever  923 , coupled together with connector or fastener  921 . 
     As shown in  FIGS. 9C and 9D , traction wheel housing  910  comprises wheel assembly  940  and generally rectangular left and right assembly plates  911  and  912 , respectively. Left assembly plate  911  and right assembly plate  912  each have an upper vertical flange,  917  and  918 , respectively, that are adapted to couple manually-engaged traction wheel  990  to center frame member  140 , as shown in  FIG. 4 . Wheel assembly  940  is sandwiched between and coupled to left assembly plate  911  and right assembly plate  912  with bushings  913  and  914 , washers  915 , and screws  916 , or other known types of connectors or fasteners. 
     With reference to  FIGS. 9A and 9B , wheel assembly  940  comprises wheel  941 , and left and right wheel brackets  942  and  943 , respectively. Left and right wheel brackets  942  and  943  form a housing for wheel  941 . Wheel  941  is sandwiched between and coupled to left wheel bracket  942  and right wheel bracket  943  with bushing  944  and screws or fasteners  945 . Bushing  944  is centered through wheel  941 , and allows wheel  941  to rotate. 
     Left wheel bracket  942  and right wheel bracket  943  each define an elongated slot,  946  and  947 , respectively, through which bushing  913  is inserted and coupled to post  919 , as shown in  FIGS. 9B ,  9 C and  9 D. This configuration allows wheel assembly  940  to move up and down relative to the left and right assembly plates,  911  and  912 , of the traction wheel housing  910 . The range of movement of wheel assembly  940  is guided and limited by elongated slots  946  and  947 . 
     When assembled, wheel assembly  940  defines a top member  966  and a notch  950 . As shown in  FIG. 9F , notch  950  accommodates cam and lever assembly  920 . When cam and lever assembly  920  is engaged, and as shown in  FIG. 9F , cam  922  is in contact with top member  966 . Conversely, when cam and lever assembly  920  is disengaged, cam  922  is not in contact with top member  966 . 
     The wheel assembly  940  is lowered or raised by lever  923 . When lever  923  is in a first position, for example a generally horizontal position, as shown in  FIGS. 9E and 9F , earn and lever assembly  920  is engaged, and wheel assembly  940  is raised, such that wheel  941  is raised above and not in contact with the floor or other surface. When lever  923  is moved up or down ninety degrees to a second position, for example in the direction of arrow A or arrow B, cam and lever assembly  920  is disengaged, and wheel assembly  940  is lowered, such that wheel  941  is in contact with the floor or other surface. 
     III. Automatically-Engaged Traction Wheel 
     The details of automatically-engaged traction wheel  1010  are shown in  FIGS. 10A through 10I . With reference to  FIGS. 10H and 10G , automatically-engaged traction wheel  1010  comprises traction wheel housing  1030 , motor and shaft wheel-positioning assembly  1040 , and cover plate  1050 , and is coupled together with screws  1060  or other forms of known connectors or fasteners. 
     As shown in  FIG. 10I , traction wheel housing  1030  comprises wheel assembly  1020  and generally rectangular left and right assembly plates  1031  and  1032 , respectively. Left assembly plate  1031  and right assembly plate  1032  each have an upper vertical flange,  1033  and  1034 , respectively. Vertical flanges  1033  and  1034  are adapted to couple automatically-engaged traction wheel  1010  to center frame member  140  of base frame  105 , similar to the manner in which manually-engaged traction wheel  990  is coupled to center frame member  140 , as shown in  FIG. 4 . Wheel assembly  1020  is sandwiched between and coupled to left assembly plate  1031  and right assembly plate  1032  with bushings  1035  and  1036 , washers  1037 , and screws  1038 , or other known types of connectors or fasteners. 
     With reference to  FIGS. 10A and 10B , wheel assembly  1020  comprises wheel  1021 , left and right wheel brackets  1022  and  1023 , respectively, and motor engagement member  1024 . Motor engagement member  1024  defines a notch  1028 . Left and right wheel brackets  1022  and  1023  form a housing for wheel  1021 . Wheel  1021  is sandwiched between and coupled to left wheel bracket  1022  and right wheel bracket  1023  with bushing  1025  and screws or fasteners  1026 . Motor engagement member is coupled to right wheel bracket  1023  with screws  1029  and nuts  1027 , or other known forms of connectors. Bushing  1025  is centered through wheel  1021 , and allows wheel  1021  to rotate. When assembled, threaded shaft  1042  of motor and shaft assembly  1040 , described below, extends through notch  1028 . 
     Left wheel bracket  1022  and right wheel bracket  1023  each define an elongated slot,  1061  and  1062 , respectively, through which bushing  1036  is inserted and coupled to  1039 , as shown in  FIG. 10I . This configuration allows wheel assembly  1020  to move up and down relative to the left and right assembly plates,  1031  and  1032 , of the traction wheel housing  1030 . The range of movement of wheel assembly  1020  is guided and limited by elongated slots  1061  and  1062 . 
     Motor and shaft wheel-positioning assembly  1040  is shown in  FIGS. 10C through 10F . With reference to  FIG. 10E , motor and shaft assembly  1040  comprises motor  1041 , threaded shaft  1042 , motor electrical assembly  1070 , bracket  1043 , connector block  1044  and collar  1045 , and is coupled together with screws or fasteners  1046  and  1047 . Motor electrical assembly  1070 , bracket  1043 , connector block  1044  and collar  1045  ride up and down as the threaded shaft  1042  turns. With reference to  FIG. 10F , motor electrical assembly  1070  comprises circuit board  1072  and housing  1071 , which are coupled together with screws or fasteners  1073 . 
     In a preferred embodiment, automatically-engaged traction wheel  1010  is motion sensitive. Circuit board  1072  includes a Hall Effect sensor  1082  that controls motor  1041 . Hall Effect sensor  1082  responds to a small magnet  1083  embedded in wheel  1021 , as shown in  FIG. 10A . When the mobile cart base is in motion and wheel  1021  is spinning, the magnet  1083  is effectively sending an “on/off” signal to the Hall Effect sensor  1082 . 
     When wheel  1021  is not spinning, the Hall Effect sensor  1082  does not detect the “on/off” signal from magnet  1083 , and motor  1041  turns threaded shaft  1042  to a first position such that wheel assembly  1020  is raised relative to the traction wheel housing  1030  and wheel  1021  is no longer in contact with the floor or other surface. When wheel  1021  is spinning, the Hall Effect sensor  1082  detects the “on/off” signal from the magnet  1083 , and motor  1041  turns threaded shaft  1042  to a second position such that wheel assembly  1020  is lowered relative to the traction wheel housing  1030  and wheel  1021  is in contact with the floor or other surface. 
     Circuit board  1072  also includes a vibration sensor chip  1081 . When the mobile cart is in motion, the vibration sensor chip  1081  causes motor  1041  to turn threaded shaft  1042  so as to lower wheel assembly  1020 , such that wheel  1021  is in contact with the floor or other surface. 
     In an alternate embodiment, automatically-engaged traction wheel  1010  is operated by an on/off switch or button, which may be located on the mobile cart base  800 , or the upper working section  8210  or the intermediate section  8230  of the mobile cart  8200 . 
     Motor  1041  receives power from the on-board battery cells  710  and  720  through interconnect board  621 , shown in  FIG. 6 , through two terminals  1048  located on the outer side of motor  1041 , shown in  FIGS. 10D and 10E . 
     The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.