Abstract:
A utility cart is provided which minimizes damage caused by impact with objects, particularly for use on a windy airport tarmac, the cart comprising a frame having main wheels bearing most of the cart&#39;s weight, these main wheels being fitted with latch-type brakes. The cart has a top structure, such as a roof, which extends horizontally above the frame, the periphery of which approximates or extends beyond the periphery of the frame. The top structure is normally supported above the cart&#39;s frame using three or more laterally collapsible supports for permitting the top structure to be displaced laterally while remaining substantially horizontal so as to minimize energy transfer upon lateral impact of the periphery of the top structure with an object. Each of the preferred collapsible supports comprises a tubular member elastically sandwiched between top and bottom plates mounted to the top structure and frame respectively.

Description:
FIELD OF THE INVENTION 
     The present invention relates to wheeled carts used for carrying a payload such as baggage, particularly those used in the airport environment which is subject to wind and around equipment which is sensitive to impact damage. 
     BACKGROUND OF THE INVENTION 
     An airport tarmac is just one environment in which windy conditions can adversely affect the serviceability of utility carts. The airport tarmac is a utilitarian surface, used primarily by support personnel in the business of servicing aircraft and transporting baggage. Baggage is some times transported on carts towed behind small motorized vehicles. Other carts are hand-powered. In the case of commuter aircraft, passengers also access the tarmac for boarding the aircraft from the ground. In such cases, it is usual for the airline operator to park a small hand-powered cart between the terminal building and the aircraft. 
     Passengers place their baggage on this cart as they leave the terminal. Airline personnel may also place the baggage on such a cart for passengers to pick up as they deplane and approach the terminal. 
     The cart is manually pushed about the tarmac. When placed in the vicinity of aircraft, the cart is subject to aircraft jet blast, propeller wake, and general wind conditions unimpeded by barriers. Baggage carts present a large wind catching surface, particularly when loaded. The above incidents of wind can cause the carts to roll on their wheels, to overpower friction brakes, or to pivot or skid about a non-rotating wheel or wheels. A moving cart is a hazard for personnel, but more frequently becomes a hazard to aircraft. Incidents of an impact of a cart with an aircraft are known and damaging. Contact of a cart is typically between the top or roof of a cart and the highly engineered and easily damaged skin of an aircraft fuselage or with the propeller which can result expensive repair and service costs. 
     In U.S. Pat. No. 5,862,884 issued to Applicant, the problem of wind has been partially addressed in the implementation of an airfoil on a portable wheelchair lift for use on airport tarmacs. While the use of airfoils on a lift or a cart convert lateral wind loading to a downward force for resisting overturning, it does not address the eventual impact issues with a cart, whether during handling or due to wind. 
     A variety of prior art carts are in use, none of which have proven particularly satisfactory to the airlines in part because: 
     they are hard to push; 
     the carts are insufficiently resistant to being wind driven into the aircraft; or 
     regardless of the reason for an impact, the contact of a cart and an aircraft results in damage. 
     It is known to equip prior art carts with brakes, as described in U.S. Pat. No. 3,651,894 to Auriemma. Auriemma discloses a serving cart with friction brakes, operated with a dead-man arrangement of a handle and drum-brakes with an actuating cable therebetween. A spring normally applies braking pressure until the handle is pushed or pulled. In U.S. Pat. Nos. 3,986,582 to Dye and 4,084,663 to Haley, latching type dead-man braking arrangements disclosed for a serving cart and carriage respectively. Both Dye and Haley disclose braking systems which use spring-biased pins which engage complementary opening in the sides of supporting wheels. Dye locates supporting wheels mid-cart and both are fitted with the brakes to avoid rotation. 
     When the operator releases the brake however, operator inattention can result in a collision with other objects. In the context of an airport tarmac, accidental contact of lower portions of the cart are rarely significant, being with tires or other sturdy structures. However, contact of the top of the cart can happen and is usually with the sensitive aircraft fuselage or a propeller. 
     No known prior art utility carts employ energy absorbing means about the cart&#39;s upper periphery. 
     Accidental impact has been addressed by others is situation where the damage-sensitive object is moving. In U.S. Pat. No. 2,546,026 to Coon for instance, an early use of a closed coil spring is disclosed as a mounting between an antenna and an automobile. Lateral impact of the antenna causes the spring to deflect, absorbing the energy and avoiding damage to the antenna. In U.S. Pat. No. 5,199,814 to Clark et al., a signpost is fitted with coupling to a base, the coupling permitting the signpost to pivot over from an upright to a prone position when struck by a vehicle. Deflection of the signpost limits damage to the post and to the vehicle. The coupling arrangement utilizes a tension cable between the base and the signpost. Deflection of the signpost and cable compresses a spring within the signpost, allowing the signpost to move and creating a righting force. The top of the post can rotate to the ground if run completely over by the offending vehicle. 
     In the context of a utility cart used at an airport, the upper structure often serves also as a load-carrying platform. In the case of the prior art coil spring mounting of Coon, the spring is unsuitable for supporting vertical loads, tending to buckle or collapse upon itself. The signpost coupling of Clark et al. has a narrow point of contact which aids in its rotation but does not assist, nor anticipate incorporation of a load-supporting structure while continuing to permit energy-absorbing deflection when struck from the side. 
     Regarding the braking issue, prior art use of friction brakes is limited to instances where the lateral forces can exceed the frictional pre-load. The extraordinary wind loading imposed on a cart on an airport tarmac can easily overcome friction brakes, particularly if the effectiveness of the brakes depends on wear or maintenance. 
     Those prior art carts which are fitted with latching type brakes have not dealt with the impact issue which can also occur when an operator has consciously released the brakes. 
     Therefore, there is a demonstrated need for a utility cart which has a system of supporting wheels and brakes which ensures immobility when stopped and which has an energy absorbing periphery for minimizing or eliminating impact damage regardless of the state of the cart. 
     SUMMARY OF THE INVENTION 
     A novel utility cart is provided which permits safe operation around sensitive equipment, particularly due to the cart&#39;s ability to absorb the energy of accidental impact therewith. In the case of operation in windy environments, the cart is further resistant to induced movement which can contribute to such accidental impact. Induced movement includes that due to wheel skidding, cart rotation or brake failure. Factors contributing to the cart&#39;s newfound sure-footedness includes: concentrating the carts weight on two or more main wheels for minimizing wind-induced rotational moments and for lessening wheel skidding, implementing positive latching type brakes on those main wheels to avoid brake failure, and applying an airfoil roof for lessening the overturning moment and increasing the wheel loading for reinforcing the anti-skid advantages. 
     Therefore, in a broad apparatus aspect, a utility cart is provided which minimizes damage caused by impact with objects, the cart comprising a wheeled frame having a top structure extending horizontally above the frame, the top structure having a periphery which approximates the periphery of the frame; and supports for normally supporting the top structure above the frame, the supports being laterally collapsible for permitting the top structure to be displaced laterally while remaining substantially horizontal so as to minimize energy transfer upon lateral impact with the periphery of the top structure. 
     Preferably, three or more upright-biased supports are used to support the top structure, such as a roof, so that payloads can supported thereon yet, under lateral impact, they will still deflect laterally, absorbing the energy of the impact. The preferred support is a tubular member sandwiched between top and bottom plates and having a tensioning means secured between the top and bottom plates for elastically connecting the top and bottom plates. One such a tensioning member is a cable having a spring compressed between the bottom plate and the bottom end of the cable. 
     When a roof is employed as the top structure, it is preferably shaped as an airfoil for interacting with airflow flowing thereover so as to generate downward forces with the associated advantages therewith. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a perspective view of a utility cart, typically used as an airport tarmac baggage cart, which implements several embodiments of the present invention, the top periphery being formed as a roof; 
     FIG. 1 b  is partial perspective view of an alternate top structure for the cart of FIG. 1 a , the illustrated periphery having no roof but still having an energy-absorbing function; 
     FIG. 2 is a fanciful side view of a cart according to an embodiment of the invention which has impacted an aircraft fuselage wherein the roof structure has deflected, avoiding damage to the aircraft; 
     FIG. 3 a  is a side view of a cart according to FIG. 1 a;    
     FIG. 3 b  is an end view of a cart according to FIG. 1 a;    
     FIG. 4 a  is a side, cross-sectional view of a simplified flat top structure mounted to supports depicted in the normally upright position; 
     FIG. 4 b  is a side, cross-sectional view according to FIG. 4 a  illustrating deflected top structure and supports after a lateral impact; 
     FIG. 5 a  is a side, cross-sectional view according to FIGS. 4 a  and  4   b  illustrating the support in its normally upright (solid lines) and in the deflected position (phantom lines) positions; 
     FIG. 5 b  is a side, cross-sectional view of an alternate form of the support using an elastic tensioning means; 
     FIG. 6 is a partial side view of the main supporting wheels, a dead-man braking system and a hand-actuating handle as applied to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Having reference to FIG. 1, a utility cart  1  comprises a rigid frame  2  supported on main pneumatic wheels  3  and secondary casters  4 . The cart is about an airport tarmac  5  on wheels  3  and  4 . The cart&#39;s frame  2  is substantially a rectangular parallelepiped stick-frame construction of a mixture of round and square tubing. Significant use of aluminum tubing material aids in minimizing the cart&#39;s weight. 
     Referring to FIGS. 1 a  and  3   a , the cart&#39;s frame  2  is supported upon the two main wheels  3  which are fitted with a braking system  6 . The main wheels are located near the cart&#39;s center of gravity G, supporting about 85% of the cart&#39;s weight and ensuring low-rolling resistance. The secondary casters  4  pick up the remaining 15% and enable ease of turning. Tertiary safety casters  7  are normally not in contact with the tarmac  5  may do so if the cart is rocked or if improperly loaded. 
     Two parallel baggage-supporting shelves  8  are arranged in the cart&#39;s frame  2 , covered by a roof  9 . The roof  9  is a substantially horizontal top structure  10  which has peripheral edges  11  which extend beyond the plan or periphery of the frame  2 . Preferably, the profile of the roof  9  is formed as an airfoil—i.e. having a convex upper curved surface or peak. 
     Accordingly, when wind or jet blast impinges on the cart  2 , the central positioning of the main support wheels  3  tends to balance the resulting rotational torque produced. Further, as the bulk of the cart&#39;s weight is on the braking wheels  3 , maximal sliding resistance is generated between the wheels  3  and the tarmac  5 . Finally, the wind also flows over the airfoil roof  9 , producing a downward force and thereby adding to the wheel&#39;s normal force and further aiding in resisting overturning and rotation. 
     The roof  9  may also be used as an additional baggage-supporting shelf (see FIG. 2) and thus is also capable of supporting typical baggage loads. The roof  9  can be fitted with a small rail to prevent baggage from sliding off (not shown). 
     As shown in FIG. 2, the top of the cart  2  is typically the point of first contact with objects such as an aircraft  12 . Accordingly, the top structure  10  is designed to deflect laterally and absorb the energy of any contact or impact having a lateral component. 
     Referring to FIG. 1 b , the roof of FIG. 1 a  is alternatively replaced with a mere bumper frame  13 . As is the case with a roof-type structure  9 , the periphery  11  of the top structure  10  of the bumper frame  13  extends laterally from the plan of the frame  2 , so as to increase the probability that the bumper  13  will be the first to contact the aircraft  12  and thus absorb impact-energy. Additional resilient nosing material (not detailed) can be added to the periphery  11  to provide additional contact protection. 
     In any case, the top structure  10  is itself rigid, but is supported on movable supports  15 . 
     Having reference to FIGS. 4 a ,  4   b  and  5   a , each support  15  comprises a base  16 , formed in the frame  2 , a bottom plate  19 , a tubular member  18 , a top plate  17  and a tensioning means  20 . The top plate  17  is mounted to the top structure  10 . Three or more supports  15  are provided so that the top structure  10  remains substantially horizontal when deflected laterally (FIGS.  2 , 4   b ) thereby preventing spillage of any supported baggage. 
     The tensioning means  20  extends between the top plate  17  and the bottom plate  19 , elastically sandwiching the tubular member  18  therebetween. The tubular member  18  is a tubular body having a bore  21  and parallel right planer top and bottom ends  22 , 23 . The top plate  17  has a planer surface  24  and the bottom plate  19  has a planer surface  25  which is parallel to and faces the top plate&#39;s planer surface  24 . The tubular member&#39;s planer top and bottom ends  22 , 23  are complementary to the top and bottom plate planer surfaces  24 , 25 . Without further structure, a vertical load on the top plate  17  is supported by the tubular member  18  and bottom plate  19 . Practically however, such an arrangement is unstable and slight lateral movement causes the tubular member  18  and the supported top structure to collapse side ways. 
     Accordingly, the tensioning means  20  comprises an elongated connector or cable  26  extending between the top and bottom plates  17 , 19  and through bore  21 , increasing the support&#39;s overall stability. Typically, the cable  26  is formed of wire rope which is substantially inextensible, but is weak laterally so that it may be readily deflected to the side. 
     The cable  26  has top and bottom ends  27 , 28 , the top end  27  being secured to the top plate  17 . The cable  26  extends through the bore  21  and through the bottom plate  19 . The bottom end  28  of cable  26  is affixed to the bottom of a compression spring  30 . The compression spring  30  is preloaded by sandwiching it between a spring stop  31 , which bears against the bottom plate, and the bottom end  28  of the inextensible cable  26 . For assembly purposes, the spring stop  31  is installed within the bore of a tubular portion of the frame  2  and affixed therein using a retaining pin  32 . 
     As shown in FIG. 4 b  and the shadow lines in FIG. 5 a , upon lateral deflection of the top structure  10 , such as from impact, the tubular member  18  pivots and the tensioning means  20  absorbs the energy of the deflection. 
     It can be seen that use of a tensioning means  20  which extends through the bore  21  of the tubular member  18  also guides the member and prevents its dislodging from the top and bottom plates  17 , 19 . However, a more preferred arrangement is to provide a centrally-located protuberance  33  in the center of each of the top and bottom plates  17 , 19 . Accordingly, the bore  21  of the tubular member  18  is constrained substantially concentric with the top and bottom plates  17 , 19 , ensuring its return to its original upright position when the deflecting force is removed. 
     As stated above, incidents of accidental impact can be minimized if the cart  2  is not able to move except when consciously operated. To that end, a dead-man braking system  6  is provided. If an operator is not actively moving the cart  2  then the braking system  6  engages, positively locking the wheels  3  which then must skid if the cart  2  is to move at all. 
     As shown in FIG. 6, the braking system  6  utilizes latch-type brakes  40  fitted to each of the two main wheels  3 , and a hand-release push-handle or actuator  41 . Each brake  40  comprises a disc  42  co-rotating with each wheel  3 . A plurality of circumferentially-spaced index slots  43  are cut radially into the disc  42 . A spring-loaded latch  44  radially engages the slots  43  to positively prevent disc and wheel rotation. The latch  44  extends from a lever  45 , pivoted from the frame  2 . A spring  46  is affixed to the lever for biasing the latch into engagement with the disc slots  43 . The push-handle actuator  41  is connected to the lever using a release cable  47 . The release cable  47  is wrapped around a cam  48  on the actuator  41 . When the push-handle actuator  41  is rotated for pushing operation of the cart  2 , the rotation is converted into a release cable-pulling action. The release cable  47  extends about a pulley  49  and runs beneath the cart  2  to the brake&#39;s levers  45 . For operating the brakes  40  simultaneously, a bar and V-yoke  50  (not detailed) connects both levers  45  for both brakes  40  and the release cable  47  connects to the apex of the yoke  50 . 
     The apparatus of the invention may be employed whether the cart  2  is standing or is moving. When moving, the operator rotates the push-handle actuator  41  for releasing the brakes  40  and pushes or pulls the cart  2  which can subsequently impact an object  12 . When standing, the brakes  40  are positively engaged, minimizing the opportunity for the cart to move, but if it does skid, or another object  12  moves into contact with it, the structure  10  on the novel cart deflects. 
     When an impact of the top structure  10  results in a lateral force component, the top structure deflects laterally, rotating the supports  15  for absorbing the impact energy. Lateral deflection causes the tubular member  18  to rotate, laterally bending the cable  26  causing each top plate  17  to pull their respective cables  26 , drawing each cable  26  upwardly through their bottom plate  19 . The bottom end  28  of each inextensible cable  26  compresses its spring  30 , increasing the spring&#39;s compression and the tension in the cable  26  for producing increased resistance to deflection as the support  15  rotates. Depending upon whether baggage is also being carried on the top structure  10  it may or may not self-right itself under the increased tension in the cable  26 . 
     An example of a utility cart which is based upon the above elements is a 1.34 m high, 2.34 m long by 0.84 m cart, constructed substantially of 6061 T-6 aluminum and having a tare weight of about 85 kgs. With two shelves, the cart has a capacity of about 350 kgs and can be manipulated by one person. Fitted with latch-type brakes on the two main pneumatic wheels and using an airfoil roof as the top structure, the cart is stable in a 100 kph wind. Wind effect and stability is obviously a function of the nature and arrangement of the baggage on the cart. 
     As shown in FIG. 5 b , other tensioning means such as a low-creep elastic cord  51  could be utilized for tensioning the supports, thereby replacing both the inextensible cable and the compression spring. 
     While various embodiments to the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.