Abstract:
A medical or dental cart for carrying medical or dental instruments. The cart comprises a base, a back pillar mounted on the base, a boom arm connected to the back pillar using hinged joints, and an instrument carrier connected to the boom arm using hinged joints. The instrument carrier is configured to carry medical or dental instruments. The hinged joints are configured such that the boom arm is rotatable toward the base and away from the base, and such that the instrument carrier is held at a substantially fixed orientation relative to the base throughout the range of motion of the boom arm. The hinged joints are also configured to impede sideways rotation, thereby impeding movement of the instrument carrier in a substantially sideways direction and thus impeding sideways tipping of the cart.

Description:
RELATED APPLICATIONS 
       [0001]    The application is a continuation of PCT Patent Application No. PCT/CA2015/050111 filed on Feb. 17, 2015, entitled “MEDICAL CART” which claims priority from the U.S. Provisional Patent Application No. 61/940,750, filed on Feb. 17, 2014, entitled “MEDICAL CART”. The entirety of the contents of the PCT Patent Application No. PCT/CA2015/050111 and the U.S. Provisional Patent Application No. 61/940,750 are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates to the field of medicine, and more specifically to mobile mounting of devices used in performing medical procedures. 
       BACKGROUND 
       [0003]    Medical professionals often need to position instruments, such as cameras, position trackers, patient monitors, display screens, laptop computers, etc. within a relatively short distance from the patient treatment region (eg, surgical field) at a height similar or higher than that of the patient. 
       SUMMARY 
       [0004]    Embodiments of the current invention provide a mobile cart on which instruments such as cameras, position trackers, patient monitors, display screens, laptop computers, etc. may be mounted, with the following features:
       1. Allows easily and rapidly changing the location and height of the mounted instruments by a clinician, including placing it over the patient.   2. Requires very small floor space at some distance from the treatment field, so minimizes interference with access to that field.   3. Allows positioning multiple devices together, stacked up vertically.   4. May be easily, rapidly and safely moved to/from storage and between treatment rooms.   5. Requires a small storage space.   6. Weighs only about 20-25 kg in total when designed to carry up to 5 kg of instruments.       
 
         [0011]    In accordance with an aspect of an embodiment of the invention there is provided a medical or dental cart. The cart may comprise a base defining a base plane, and the base may be substantially horizontal. The base may have a plurality of supports for supporting the base for motion along a surface parallel to the base plane. The plurality of supports may include at least two rear supports and at least one front support. The at least two rear supports may define a rear support axis extending between the at least two rear supports parallel to the base plane. The at least one front support may be displaced in a frontward direction, parallel to the base plane, from the rear support axis. The at least one front support may be configured to support the base in a front support direction. The cart may further comprise a back pillar mounted vertically on the base. The back pillar may define a back pillar axis that is substantially orthogonal to the base plane. The back pillar may be mounted to the base such that the back pillar axis intersects the base plane closer to the rear support axis than to the front support direction. The cart may further comprise an instrument carrier, which may be configured to carry medical or dental instruments. The cart may further comprise boom arm, which may be connected to the back pillar and the instrument carrier using hinged joints. The cart may further comprise a link arm, which may be connected to the back pillar and the instrument carrier using hinged joints. Hinged joints of the boom arm and the link arm may be configured to hold the instrument carrier at a substantially fixed orientation relative to the base plane throughout the range of motion of the boom arm and the link arm. The hinged joints on the back pillar may be positioned and oriented such that the boom arm may be rotatable towards the base to hold the instrument carrier substantially adjacent to the back pillar and the base plane during transport, and such that the boom arm may be rotatable away from the base to elevate and move the instrument carrier in the frontward direction relative to the back pillar axis and the at least one front support. The hinged joints may be configured to impede sideways rotation, thereby impeding movement of the instrument carrier in a substantially sideways direction to impede sideways tipping of the cart. 
         [0012]    In accordance with a further aspect of an embodiment of the invention, the at least one front support may be configured to provide rotation of the base about the back pillar axis. 
         [0013]    In accordance with a further aspect of an embodiment of the invention, each support in the at least one front support may be an omni-directional support, which may be configured to move the base in any direction parallel to the base plane. 
         [0014]    In accordance with a further aspect of an embodiment of the invention, the instrument carrier may be substantially irrotational about the back pillar axis relative to the base plane. 
         [0015]    In accordance with a further aspect of an embodiment of the invention, the hinged joints on the back pillar may be adjustable to stably support the instrument carrier in a plurality of different positions. When in different positions in the plurality of different positions, the instrument carrier may be at different heights from the base. 
         [0016]    In accordance with a further aspect of an embodiment of the invention, the instrument carrier may comprise a support platform for providing a support surface. The instrument carrier may further comprise a pivotal coupling for attaching the support platform to a distal end of the boom arm. The distal end of the boom arm may be spaced from the back pillar. The pivotal coupling may be configured such that the support platform is pivotable relative to the back pillar axis. The pivotal coupling may also be configured to hold the support platform at a substantially fixed orientation relative to the base plane throughout the range of motion of the boom arm and the link arm. 
         [0017]    In accordance with a further aspect of an embodiment of the invention, the base may be configured, and oriented relative to the back pillar, the boom arm, and the instrument carrier, to support without tipping a forward tipping moment. The forward tipping moment may result from a displacement of the boom arm and the instrument carrier in the frontward direction from the back pillar. 
         [0018]    In accordance with a further aspect of an embodiment of the invention, the base may be configured, and oriented relative to the back pillar, the boom arm, and the instrument carrier, to support without tipping a forward tipping moment. The forward tipping moment may result from a displacement of the boom arm and the instrument carrier in the frontward direction from the back pillar, and a 5 kg weight supported by the instrument carrier. 
         [0019]    In accordance with a further aspect of an embodiment of the invention, the base may be configured, and oriented such that a maximum forward tipping moment bearable by the base without tipping may be determinable. The maximum forward tipping moment may be a product of a forward tipping force and a frontward displacement in the frontward direction. The forward tipping force may be borne by the back pillar, acting toward the base plane, and may be displaced by the frontward displacement from the back pillar axis. The base may be further configured, and oriented such that a maximum backward tipping moment bearable by the base without tipping may be determinable. The maximum backward tipping moment may be a product of a backward tipping force and a backward displacement in a backward direction opposite to the frontward direction. The backward tipping force may be borne by the back pillar, acting toward the base plane, and may be displaced by the backward displacement from the back pillar axis. The maximum backward tipping moment may be less than half the maximum forward tipping moment. 
         [0020]    In accordance with a further aspect of an embodiment of the invention, the base may be configured, and oriented such that a maximum first sideways tipping moment bearable by the base without tipping may be determinable. The maximum first sideways tipping moment may be a product of a first sideways tipping force and a sideways displacement in a first sideways direction. The first sideways direction may be orthogonal to the frontward direction and the back pillar axis, and may be orientated away from the back pillar axis towards one of the at least two rear supports. The first sideways tipping force may be borne by the back pillar, acting toward the base plane, and may be displaced by the sideways displacement from the back pillar axis. The base may be further configured and oriented such that a maximum second sideways tipping moment bearable by the base without tipping may be determinable. The maximum second sideways tipping moment may be a product of a second sideways tipping force and a second sideways displacement in a second sideways direction. The second sideways direction may be opposite to the first sideways direction. The second sideways tipping force may be borne by the back pillar, acting toward the base plane, and may be displaced by the sideways displacement from the back pillar axis. The maximum first sideways tipping moment and the maximum second sideways tipping moment may each be less than half the maximum forward tipping moment. 
         [0021]    In accordance with a further aspect of an embodiment of the invention, each support in the plurality of supports may be one of a wheel and a ball, which may provide rolling motion along the surface parallel to the base plane. 
         [0022]    In accordance with a further aspect of an embodiment of the invention, the instrument carrier being held substantially adjacent to the back pillar and the base plane during transport may define a storage and transport position. In the storage and transport position, the base may be configured such that the back pillar is tippable about the rear support axis, such that the at least two rear supports may support an entire weight of the cart. Each support in the at least two rear supports may be a fixed, uni-directional support, which may be configured to move the base in a horizontal direction orthogonal to the rear support axis. 
         [0023]    In accordance with a further aspect of an embodiment of the invention, the cart may further comprise a handle, which may be supported by the back pillar and spaced from the base for holding and transporting the cart in the storage and transport position when the back pillar is tipped about the rear support axis such that the at least two rear supports support the entire weight of the cart. 
         [0024]    In accordance with a further aspect of an embodiment of the invention, the at least two rear supports may comprise a first side support closest to a first side of the base and a second side support closest to a second side of the base. The second side may be opposite the first side. The second side support may be displaced from the first side support by between 10 and 50 cm. The at least one front support may define a front support axis, which may intersect the at least one front support and may be substantially parallel to the rear support axis. The front support axis may be displaced from the rear support axis by between 10 and 50 cm. 
         [0025]    In accordance with a further aspect of an embodiment of the invention, the boom arm, link arm, instrument carrier, and back pillar may each be made of a lightweight material. The base may be made of a heavier material. The heavier material may have a density of at least twice the lightweight material. 
         [0026]    In accordance with a further aspect of an embodiment of the invention, a centre of mass of the cart may be displaced within a centre of mass range. The centre of mass may be movable within the range by movement of the instrument carrier and the boom arm. 
         [0027]    In accordance with a further aspect of an embodiment of the invention, a total weight of the cart may be less than 25 kg. In each different position in the plurality of different positions, the instrument carrier may be configured and positioned to support a weight of up to 5 kg without tipping the cart in any direction. 
         [0028]    In accordance with a further aspect of an embodiment of the invention, in each different position in the plurality of different positions, the instrument carrier may be substantially parallel to the back pillar axis. 
         [0029]    In accordance with a further aspect of an embodiment of the invention, in the storage and transport position, the instrument carrier may be held substantially adjacent to the back pillar and the base plane by a spring. 
         [0030]    In accordance with a further aspect of an embodiment of the invention, the back pillar may comprise a recess for receiving the boom arm when in the storage and transport position, such that the boom arm in the storage and transport position may be substantially parallel to and coincident with the back pillar axis. 
         [0031]    In accordance with a further aspect of an embodiment of the invention, each support in the plurality of supports may define a diameter. The diameter of each support in the at least two rear supports may be at least 50% larger than the diameter of each support in the at least one front support. 
     
    
     
       DRAWINGS 
         [0032]    The person skilled in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicants&#39; teachings in any way. 
           [0033]      FIG. 1  illustrates a cart according to one embodiment of the present invention, with its boom arm in the operative position to carry instruments during a medical or dental procedure. 
           [0034]      FIG. 2  illustrates a cart with its boom arm folded down in the storage and transport position according to one embodiment of the present invention. 
           [0035]      FIG. 3A , in a cross-sectional view, illustrates a portion of the cart, including the adjustable instruments support structure, with the boom arm extended as shown in  FIG. 1 . 
           [0036]      FIG. 3B , in a cross-sectional view, illustrates a portion of the cart, including the adjustable instruments support structure and the base, with its boom arm in a storage and transport position as shown in  FIG. 2 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0037]    Referring to  FIGS. 1-3 , the main structural parts of the cart  10  are mobile base  100 , back pillar  103  mounted vertically on top of the base  100  and orthogonal to the base plane  140 , a hollow boom arm  112  connected to the back pillar  103  through hinged joint  34 , and an instrument carrier  104  connected to boom arm  112  through hinged joint  36  and held substantially parallel to the back pillar axis  151  using link arm  32 . Four wheels may be fixed to the base  100 , with the two front wheels  91 ,  92  being omni-directional wheels (or balls), able to move in any direction, including sideways. The wheels (or balls) may be configured to allow the cart  10  to roll along the ground, either to and from storage, or into position at a desired distance from the treatment field. The two front wheels  91 ,  92  may be displaced in the frontward direction  161  relative to the back wheels  101 ,  102 . The instruments to be carried by the cart  10  may be attached to instrument carrier  104 , either through rigid clamps or through pivotal couplings  38 , allowing each instrument to be rotated and/or tilted individually. 
         [0038]    The instruments may also be supported by a support platform, which may be connected to the boom arm  112  and instrument carrier  104  via pivotal coupling  38 . In a preferred embodiment, the pivotal coupling  38  may be configured such that the support platform is pivotable about an axis parallel to the back pillar axis  151 . The attitude (azimuth and elevation) of each device or support platform attached to instrument carrier  104  can be adjusted using a pivotal coupling  38 , which can be a friction/lockable ball joint or, preferably, two separate rotational joints. The pivotal coupling  38  may thus be configured to hold the instruments or support platform in a fixed position, subject to manual rotation and or/tilting, such that the instruments or support platform can maintain a substantially fixed orientation relative to the base plane  140  throughout the range of motion of the boom arm  112  and the link arm  32 . 
         [0039]    Link arm  32  can keep the instruments at a constant attitude throughout the range of motion of the boom arm  112 , and can be hidden inside hollow boom arm  112 . Power and signal cables may be hidden inside back pillar  103 , boom arm  112  and instrument carrier  104 , protecting them from damage and reducing visual clutter. A power cable may exit the base  100  at the back, between back wheels  101 ,  102 . Excess cable can be wrapped around spindle  27  (or two opposing hooks) at the back of back pillar  103 . Compression spring  40  provides support for the boom arm  112  to counter gravitation when it is open, and a positive locking force when the boom arm  112  is closed. Ballast  50  may be mounted above the back wheels  101 ,  102  to provide stability to, and impede tipping of, the cart  10 . 
         [0040]    Foot rests  90  on the sides of the base  100  allow users to hold the base  100  stable on the floor while pulling or pushing the instrument carrier  104  during movement of the boom arm  112  into and out of the storage and transport position, and throughout the range of motion in the operative position. Baskets  108 ,  109  on the sides of the cart  10  provide storage space for small accessories and literature. Handrail  105  can allow a user to easily move the cart  10 , when in the storage and transport position, by tilting the back pillar  103  about the rear support axis  150  and rolling it on its back wheels  101 ,  102  (similar to a dolly/hand-truck). In a preferred embodiment, when in the storage and transport position, back wheels  101 ,  102  may support an entire weight of the cart, and may be configured to provide movement of the base  100  along the ground in a direction that is orthogonal to the rear support axis  150 . While the back wheels  101 ,  102  may support an entire weight of the cart  10  and can provide smooth travel over uneven surface during long transport, the front wheels  91 ,  92  are lifted off the ground during the transport. The back wheels may, therefore, have a diameter larger by 50% or more than the front wheels. 
         [0041]    In one embodiment, a laptop computer  120  and an enclosure  130  containing a stereoscopic camera and an illumination panel are attached to the instrument carrier  104 . 
         [0042]      FIGS. 1 and 3A  show the cart  10  in the operative position, where the base  100  may be positioned next to the patient&#39;s bed or chair, and the instruments may be placed above and next to the treatment field anywhere in the patient&#39;s body. The combination of the upward force applied by compression spring  40  and the friction in hinged joint  34  can hold the instruments in a desired position.  FIG. 2  shows the cart  10  in the storage and transport position, ready to be moved or stored. To open the cart  10 , the user may place one foot on footrest  90  and pull instrument carrier  104  forward and up. 
         [0043]    The force applied by spring  40  may be adjusted to balance the weight of the instruments being carried (payload) when the boom arm  112  is in different positions. Preferably, spring  40  is a gas spring and the internal pressure may be adjusted to control the force. Alternatively, or in addition, the force may also be adjusted by moving one end of the spring  40  closer to, or farther from, the other end of the spring  40  using a screw. To allow stable positioning over a wide range of boom arm elevation angles, for example, from  30  degrees below horizontal to  45  above horizontal, friction may be added to hinged joint  34 . The friction in hinged joint  34  may be adjusted, at the factory and later by users, to provide a balance between ease of movement on the one hand, and resistance to “drift” of the boom arm  112  from its intended position on the other. The friction in hinged joint  34  may be provided by a washer-like friction plate surrounding the axle of hinged joint  34 , pressed against an opposing steel (or other friction-coated) surface by a spring force. The force of the friction spring can be adjusted by the user using an adjustment screw. 
         [0044]    To adjust the height and position of instrument carrier  104 , the user may grab and move the instrument carrier  104 , or the instruments attached to it. Movement of instrument carrier  104  and the boom arm  112  in a substantially sideways direction may be impeded by hinged joints  34 ,  35 . In some embodiments, the hinged joints  34 ,  35  may be located at least partly within a recess  60  of the back pillar  103 , such that the portions of the back pillar  103  forming the sidewalls of the recess  60  themselves prevent substantial sideways motion of the boom arm  112 . Movement of just the instrument carrier  104  in a substantially sideways direction relative to the boom arm  112  may be impeded by hinged joints  36 ,  37  to impede sideways rotation in order to impede sideways tipping of the cart  10 . The front wheels  91 ,  92  allow the instrument carrier  104  to move in a substantially sideways direction, since the front wheels  91 ,  92  can rotate about the back pillar axis  151  when it is located approximately between back wheels  101 ,  102 . 
         [0045]    Hollow boom arm  112  may be connected through hinged joint  36  to block  30 , which is rigidly attached to instrument carrier  104 , on one side, and through hinged joint  34  to back pillar  103 , on the other side. Link arm  32 , hidden inside hollow boom arm  112 , may be connected through hinged joint  35  to back pillar  103  on one side, and through hinged joint  37  to block  30  on the other side. Hinged joints  34 ,  35 ,  36 ,  37  may be arranged in a parallelogram, such that the link arm  32  may be kept substantially parallel to the boom arm  112 , and such that the instrument carrier  104  may be held at a substantially fixed orientation relative to the base plane  140 , throughout the range of movement of boom arm  112 . Thus, at any given point in the range of movement of boom arm  112 , instrument carrier  104  may be at a different height from the base  100 . Hinged joints  34 ,  35  may be configured to limit the range of movement of the boom arm  112 , and thus the range of movement of the instrument carrier  104 , to positions in the frontward direction relative to the back pillar axis  151 . Instrument carrier  104  may thus remain substantially parallel to back pillar axis  151  throughout the range of motion of boom arm  112 , keeping the attitude of the instruments constant as the user moves instrument carrier  104  about. In the parallelogram configuration, hinged joint  35  may be offset from hinged joint  34 , and hinged joint  37  may be offset from hinged joint  36 , to allow the boom arm  112  a range of motion from about 90 degrees below horizontal to about 45 degrees above horizontal. 
         [0046]    When the boom arm  112  is moving within its range of movement, hinged joints  34 ,  35  may impede the movement of boom arm  112  in a substantially sideways direction. Hinged joints  34 ,  35  may be configured to impede sideways rotation in order to impede sideways tipping of the cart  10 . The front wheels  91 ,  92  may allow the boom arm  112  to move in a substantially sideways direction, since the front wheels  91 ,  92  can rotate about the back pillar axis  151 . 
         [0047]    In one embodiment, the distance between the two back wheels  101 ,  102 , and the distance between the front support axis  154  and the rear support axis  150 , may each be about 10-50 cm. A plate may hold the back wheels  101 ,  102  and back pillar  103  in place. The height of hinged joint  34  from the floor may be about 90 cm, and the boom arm  112  may be about 70 cm long, allowing the bottom of instrument carrier  104  to operate at a height range of about 60-135 cm, which is sufficient for accommodating a wide range of patient treatment setups and user preferences. In this embodiment, the range of motion of the boom arm  112  may allow the range of positions of the instrument carrier  104  to include positions displaced in the frontward direction  161  relative to the front wheels  91 ,  92 . 
         [0048]    Ballast  50  may be placed above, or around, the rear support axis  150 , to counter-balance the weight of the boom arm  112 , instrument carrier  104 , and the instruments that the instrument carrier  104  carries when the cart  10  is in the operative position. The support provided by the front wheels  91 ,  92  in the front support direction  162  may also help to counter-balance the weight of the boom arm  112 , instrument carrier  104 , and the instruments that the instrument carrier  104  carries when the cart  10  is in the operative position. The front support direction  162  may be orientated to impede frontward tipping of the base  100 . 
         [0049]    The displacement in the frontward direction  161  of the boom arm  112 , the instrument carrier  104 , and the instruments that the instrument carrier  104  carries when the cart  10  is in the operative position may create a forward tipping moment. The forward tipping moment may be borne by the back pillar  103  so as to impede tipping of the cart  10 . It is contemplated that tipping moments may occur in directions other than the frontward direction  161 , such as in a backward direction opposite to the frontward direction  161 , or in a sideways direction. Since the boom arm  112  and the instrument carrier  104  may be configured such that their ranges of motion may be limited to positions in the frontward direction  161  relative to the back pillar axis  151 , a backward or sideways tipping moment would typically be smaller than a forward tipping moment. In a particular embodiment, a maximum tipping moment in the backward direction opposite to the frontward direction  161 , or in a sideways direction orthogonal to the frontward direction  161  and parallel to the base plane  140 , may be less than half of the maximum forward tipping moment (all tipping moments being measured relative to the back pillar axis  151 ). In other embodiments, the maximum tipping moment in the backward direction opposite to the frontward direction  161 , or in the sideways direction orthogonal to the frontward direction  161  and parallel to the base plane  140 , may be less than 40%, 30%, 20% or even 10% of the maximum forward tipping moment. 
         [0050]    The base  100  is configured to resist the forward tipping moment caused by the displacement of the boom arm  112  and the instrument carrier  104  in the frontward direction  161 , whether or not there is instruments attached to the instrument carrier  104 . In a preferred embodiment, the weight that may be supported by the instrument carrier  104  is about 5 kg. 
         [0051]    In one embodiment, a total weight of the cart  10  may be less than 25 kg. In a preferred embodiment, when the boom arm  112  is moving within its range of movement in the frontward direction  161  relative to the rear support axis  150 , the instrument carrier  104  may be configured and positioned to support a weight of up to 5 kg. Since movement of the instrument carrier  104  can be impeded in a substantially sideways direction, the weight of ballast  50  and base  100 , as well as the support provided by the front wheels  91 ,  92  can be sufficient to impede tipping of the cart  10  in any direction. 
         [0052]    The centre of mass  160  of the cart  10  may move. Since the cart  10  can include moving components, the centre of mass  160  may be displaced in the frontward direction  161  or in a backward direction opposite to the frontward direction  161  by movement of the boom arm  112  and instrument carrier  104 . 
         [0053]    Back wheels  101 ,  102  may be uni-directional wheels (or balls). Front wheels  91 ,  92  may be smaller omni-directional wheels 
         [0054]      FIGS. 2 and 3B  show the cart  10  in the storage and transport position, which may be used for shipping, storage or moving between locations. In this state, boom arm  112  may be at a position that is at or near an endpoint of the range of motion allowed by the hinged joints  34 ,  35 , such that boom arm  112  and instrument carrier  104  are positioned adjacent to back pillar  103 , and substantially parallel to back pillar axis  151 . Boom arm  112  may further be located in a recess  60  in the back pillar  103 , such that the boom arm  112  is aligned with the back pillar axis  151 . In this embodiment, there may be sufficient space between the back pillar  103  and the instrument carrier  104  for the user to grab the instrument carrier  104  as needed to move the cart  10  into the operative position. When the cart  10  is in the storage and transport position, spring  40  may apply a force on boom arm  113  in the opposite rotational direction than when the boom arm  113  is in the operative position, thereby applying an extra “locking” force on the boom arm  112  to prevent it from rising up unintentionally. In one embodiment, a unidirectional rotary damper may be added to one of the hinged joints  34 ,  35 ,  36 , or  37 . In another embodiment, a soft rubber bumper may be added to back pillar  103 , facing the boom arm  112 , to slow and soften the movement of the boom arm  112  into the storage and transport position. 
         [0055]    To keep the center of mass  160  of the cart  10  as low as possible, parts located above the base  100 , especially the boom arm  112  and anything connected to it, and including the back pillar  103 , may be made of either a strong plastic (such as polycarbonate) or a thin metal alloy with a high tensile strength to weight ratio, such as aluminum 6061-T6 or Chromoly steel. Alternatively, the parts located above the base  100  may be made of carbon fibre, fiberglass, or titanium. The base  100  may be made of a heavier material, such as steel, or another high-density metal or metal alloy. In a preferred embodiment, the material of the base may have a density twice as large as that of the material of the boom arm, link arm, back pillar, and instrument carrier. The weight of the base  100  may help to impede frontward tipping of the cart  10 . Ballast  50  is preferably made of a low cost material with a high specific weight, such as iron or copper. The base  100  and the sides of back pillar  103  may be covered in thin plastic sheets to make them more visually attractive. 
         [0056]    A handrail  105  may be located at the top of back pillar  103  to allow users to easily grab and tilt the cart  10  back, and to then roll it behind them (or in front of them) as they walk. The narrow wheel base of the cart  10  can reduce the likelihood that a user&#39;s leg will hit the cart  10  unintentionally during walking. Baskets  108 ,  109  may be added to the sides of back pillar  103  for the storage of accessories, without substantially increasing the overall width of the cart  10  or substantially raising its center of mass  160 . 
         [0057]    It will be understood that other variations and modifications of the invention are possibly. All such modifications and variations are believed to be within the sphere and scope of the invention as defined by the claims appended hereto.