Abstract:
The present invention configures a pushcart, in particular a baggage cart such as is used in airports, for ease of maneuverability in negotiating an escalator stairway. The cart is fitted with a front wheel assembly and pivotable rear wheel assemblies, as well as with drop-attenuating mechanisms fitted to each wheel assembly. The rear wheel assemblies each include a reverse-releasable, pivoting-lock mechanism. The drop attenuating mechanisms function when the pivotable wheel assemblies are locked in the pushcart advancing direction, and include damped-swing traction members for establishing adhesive friction in contacting the treads of a sloping escalator stairway. The traction members bear the pushcart through a damped swing if the wheel assemblies are not riding on the treads of the escalator steps. The pushcart user can readily orient the vehicle toward an escalator by slightly backing up the cart, swinging it into the desired orientation, and then, by pushing the cart forward, the rear wheel assemblies automatically lock straight ahead. Thus, the wheel drop attenuators are able to function effectively to smooth the dropping of the pushcart in case the wheels are caught on the edges of the escalator stairway as it slopes.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to pushcarts for transporting baggage and the like; in particular the invention is directed to a baggage pushcart for use in airports, train stations, etc., maneuverable to negotiate an escalator stairway. 
     2. Description of Related Art 
     In large transportation centers, such as airports, handcarts or pushcarts are usually provided to assist with moving large suitcases, trunks, bags, etc. Passengers load their baggage on the carts and travel within the airport. Escalators are usually installed within airports, and users often ride the escalators with the carts loaded with their baggage. 
     The user of such a pushcart loaded with baggage confronts difficulties when boarding an escalator. Conventionally, pivotable caster wheels are employed on the cart, typically as the front wheel(s), and the rear wheels are fixed in the cart advancing direction to ensure that the cart moves straightforward. If available room on the way to the escalator is limited, the user may consequently find it difficult to maneuver the cart to board the escalator stairway. Further, once on board the escalator, the user has to be concerned with positioning the cart wheels centrally along the length of the escalator treads lest the cart drop when the moving stairway treads begin to slope, forming the escalator steps. With a heavily loaded cart, thus having to position the wheels can be a nuisance; worse than this bother is the danger should the cart drop if the wheels are caught on the edges of the formed escalator steps. 
     A separate consideration is that airport personnel who are charged with storing the baggage pushcarts join them together in long chains for transport to designated locations. Thus joining the carts, however, makes it very difficult to move the long chain sideways. Because the rear wheels are fixed in the advancing direction as noted above, the rear wheels of the joined carts must be skidded laterally. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to configure a pushcart, in particular a baggage cart such as is used in airports, for ease of maneuverability in negotiating an escalator stairway. 
     A further object is to enable the cart to travel straightforward securely and yet to be readily moved laterally as needed. 
     The present invention configures a pushcart, in particular a baggage cart such as is used in airports, for ease of maneuverability in negotiating an escalator stairway. 
     In accordance with the invention, in a principal embodiment, the cart comprises a cart body and a plurality of wheel assemblies carrying wheels. At least two of the wheel assemblies, for example two rear wheel assemblies, each includes a pivotable wheel mount that is attached to the cart body and holds a wheel. Thus, the two rear wheel assemblies are pivotable against the cart body for running the pushcart in lateral and advancing directions. Further, each rear wheel assembly includes a releasable pivoting-lock mechanism for releasably locking its pivotable wheel mount in the pushcart advancing direction. 
     Additionally, drop-attenuating mechanisms are fitted to each wheel assembly of the plurality, for example, to a front as well as to the two rear assemblies. The drop-attenuating mechanisms include damped-swing traction members disposed at a predetermined separation from level surfaces. With the pivotable wheel assemblies locked in the pushcart advancing direction, the damped-swing traction members establish adhesive friction in contacting the treads of a sloping escalator stairway. Accordingly, if the wheel assemblies are not riding on the treads of the escalator steps, that is, if the wheels are pitched off the edge of a forming step, the traction members bear the pushcart through a damped swing. 
     The two rear wheel assemblies each includes a fixed member fastened to the cart body. A swivel joins each pivotable wheel mount to the fixed member, such that the wheel mount is pivotable against the fixed member about a vertical axis. 
     The releasable pivoting-lock mechanism includes an engagement member mounted on the fixed member of each rear wheel assembly. Each engagement member has a rearward notch oriented along the pushcart advancing direction. Each releasable pivoting-lock mechanism also comprises a stop formed for engagement with the rearward notch in the engagement member, and a stop retainer. The stop retainer is fixed to the horizontal part of the wheel mount for retaining the stop in contact with the wheel. 
     Accordingly, when the pushcart is pushed in the advancing direction, the stop is urged by frictional contact with the wheel into engagement with the rearward notch. When the pushcart is reversed slightly against the advancing direction, the stop is urged out of engagement with the rearward notch by frictional contact with the wheel such that the wheel assembly is pivotable against the cart body. 
     Furthermore, the drop attenuating mechanisms comprise damping means connected to the traction members. The damping means are configured for damping the traction members through a swing approximately equal to the specification slope of the escalator. 
     The user of a fully loaded cart embodied as described above can readily orient the vehicle toward an escalator by slightly backing up the cart reverse to its advancing direction and swinging the cart into the desired orientation. Then, by pushing the cart in its advancing direction toward the escalator, the rear wheel assemblies automatically lock straight ahead. In the principal embodiment, the front wheel assembly is fixed in the advancing direction, and with the rear wheel assemblies locked straight, the front- and rear-wheel drop attenuators are able to function effectively. The user of the cart can then board the escalator without concern for the back-and-forth cart positioning with respect to the treads of the escalator stairway. Even if the cart is brought to a stop with the wheel assemblies riding on the between-step breaks in the flat way before the stairway begins to slope, the user need not reposition the cart. If the tires and are caught on the edges of the sloping stairway, the front- and rear-wheel drop attenuators—the latter being secured into functioning position by the locking mechanisms—will smooth the dropping of the cart, either ascending or descending. Users of a pushcart embodied in accordance the present invention should especially welcome its inventive capabilities wherein the cart is heavily loaded with baggage. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a cart in accordance with one embodiment of the present invention; 
     FIG. 2 is a fragmentary, cutaway, overhead view of the right front half of the cart, as split along a line of symmetry O—O, therein illustrating a front-wheel drop attenuator; 
     FIG. 3 is a view of the front-wheel drop attenuator and the front wheel with which it is associated, seen in the direction of the arrows III in FIG. 2 on a fragment of the cart frame; 
     FIG. 4 is a view of the front wheel assembly including a piston mechanism of the front-wheel drop attenuator, with the cart frame indicated in phantom, seen in the direction of the arrows IV in FIG. 2; 
     FIG. 5 is an overhead view of a rear wheel assembly shown off the cart, including a wheel lock mechanism in combination with a rear-wheel drop attenuator; 
     FIG. 6 is a cutaway, partly in section, side elevational view of the FIG. 5 rear wheel assembly including the wheel lock mechanism in combination with the rear-wheel drop attenuator; 
     FIG. 7 is a fragmentary, enlarged-scale sectional view depicting details of the rear wheel assembly lock mechanism; 
     FIG. 8 is a fragmentary, enlarged-scale sectional view corresponding to FIG. 7; 
     FIG. 9 is an overhead view corresponding to FIG. 5; 
     FIG. 10 is a cutaway, partly in section, side elevational view corresponding to FIG. 6; and 
     FIG. 11 schematically illustrates a user and the cart loaded with baggage, riding the stairway of a descending escalator; 
     FIGS. 12-14 depict the cart alone on the descending escalator stairway, illustrating stages of the action of the front- and rear-wheel drop attenuators; 
     FIG. 15 schematically illustrates a user and the cart loaded with baggage, riding the stairway of an ascending escalator; and 
     FIGS. 16-18 depict the cart alone on the ascending escalator stairway, illustrating stages of the action of the front- and rear-wheel drop attenuators. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an airport cart as an embodiment of the present invention. The cart  1  is used at an airport for carrying and transporting baggage such as suitcases. The cart  1  is primarily composed of a cart body  2 , a handle  3 , a front wheel assembly  4 , two rear wheel assemblies  5 , a front-wheel drop attenuator  6 , a rear-wheel drop attenuator  8 , lock mechanisms  9  fitted to each of the rear wheel assemblies  5 , and a (not shown) brake mechanism. 
     Arrow D 1  in FIG. 1 indicates the forward moving (advancing) direction of the cart  1 . In the following description, “longitudinal” and “lateral” are directions defined relative to the advancing direction D 1 . Specifically, “lateral” indicates horizontal directions generally perpendicular to the direction D 1  and “longitudinal” indicates horizontal directions generally parallel to the direction D 1 . 
     The longitudinal distance between the front and rear wheel assemblies  4  and  5  (that is, the wheelbase) is, in this example, 800 mm, and is on the order of double the tread length of escalator steps. The lateral distance between the two rear wheel assemblies  5  (that is, the wheel track) is 600 mm, and the entire length of the cart  1  including the handle  3  is 1300 mm. The cart  1  is designed for a specification 25° escalator, for example. 
     As shown in FIGS. 2 and 4, the front wheel assembly  4  is a double caster construction, and more specifically is composed of a fixed portion  4   a  and two tires  4   b . The front wheel assembly  4  is carried on a support plate  61 , which is described in greater detail below, and is pivotable around a vertical axis with respect to the cart body  2 . 
     The front-wheel drop attenuator  6  chiefly comprises, as shown in FIGS. 2-4, the support plate  61 , two first oil dampers  64 , a first shaft  65 , first and second arms  68  and  71 , and first and second traction members  73  and  75 . 
     The support plate  61  is fixed at opposing ends to the front portion of the cart body  2 . The front wheel assembly  4  is disposed under the center (indicated by the dashed line  0 — 0  in FIG. 2) of the support plate  61 . The fixed portion  4   a  of the front wheel assembly  4  is fastened to the support plate  61  by bolts  62 . The support plate  61  is furnished with two coupling plates  63  symmetrically about the center axis O—O and extending from the front end of the support plate  61  near its center. The coupling plates  63  are provided with pin-receiving holes. 
     Two first oil dampers  64  are provided symmetrically on either side of the center  0 — 0 . Each first oil damper  64  chiefly comprises a cylinder  64   a , a cylinder-end joint  64   b , a piston  64   c , and a piston-end joint  64   d . The cylinder-end joint  64   b  is fixed to the forward end, in the advancing direction D 1 , of the cylinder  64   a , and is joined to the coupling plate  63  via a pin. The piston-end joint  64   d  is fixed to the rear end, in the advancing direction D 1 , of the piston  64   c , and is joined to a coupling plate  65   a , described below. 
     A first shaft  65  is rotatably supported at either end by shaft carrying members  66 . The shaft carrying members  66  are fixed to the bottom surface of the support plate  61 . As shown in FIGS. 2 and 4, two coupling plates  65   a  are non-rotatably fixed to the first shaft  65  symmetrically about the center axis O—O, extending upward. Holes for pin engagement with the piston-end joint  64   d  of the first oil damper  64  are formed in the upper portion of the coupling plates  65   a , in a position offset from the center of the first shaft  65 . A first gear  67  and a first arm  68  are fixed to opposite end portions of the first shaft  65  further outward than the shaft support member  66 . 
     The first arms  68  are fixed at one end to the ends of the first shaft  65 , and, as shown in FIG. 3, extend to a position behind the front wheel assembly  4 . A third shaft  72  joins together the other ends of the left and right first arms  68  (with respect to a user in the position of normal cart operation, as depicted in FIGS.  11  and  15 ), and is rotatably supported on both first arms  68 . The third shaft  72 , near either of the right and left ends, is fitted with the first traction members  73 , which are made of rubber or the like. 
     Each first traction member  73  has a larger outer diameter than the third shaft  72 . As shown in FIG. 3, the lower end of the first traction member  73  is positioned slightly higher than the lower end of the front wheel assembly  4  when the front wheel assembly  4  is grounded on a floor surface. 
     The second arms  71  are fixed at one end to a second shaft  69 , and, as shown in FIG. 3, extend forward of the front wheel assembly  4 . The second shaft  69  is supported by the shaft support member  66 . A second gear  70  is fixed to the second shaft  69 , and meshes with the first gear  67 , as indicated in FIGS. 2 and 3. 
     Accordingly, when the first arm  68  travels describing an arc with its center about the first shaft  65 , the first shaft  65  rotates; the rotation is transmitted via the first and second gears  67  and  70 ; the second shaft  69  rotates; and the second arm  71  travels describing an arc with its center about the second shaft  69 . An example following this travel is indicated by the dotted line in FIG.  3 . Note that the arc described by either the first and second arms  68  and  71  should be approximately the specification slope of the escalator. 
     Conversely, when the second arm  71  travels describing an arc with its center about the second shaft  69 , the second shaft  69  rotates; the rotation is transmitted via the first and second gears  67  and  70 ; the first shaft  65  rotates; and the first arm  68  travels describing an arc with its center about the first shaft  65 . 
     A fourth shaft  74  joins together the other ends of the left and right second arms  71 , and is rotatably supported on the first arms  71 . The fourth shaft  74 , near either end, is fitted with the second traction members  75 , which are made of rubber or the like. 
     Each second traction member  75  has a larger outer diameter than the fourth shaft  74 . As shown in FIG. 3, the lower end of the second traction member  75  is positioned slightly higher than the lower end of the front wheel assembly  4  when the front wheel assembly  4  is grounded on a floor surface. 
     When the first and second arms  68  and  71  spread from the state indicated by solid lines to the state indicated by dotted lines in FIG. 3, the first shaft  65  rotates, and the point of engagement of the coupling plate  65   a  and the piston-end joint  64   d  moves forward as well as downward. This inclines the first oil damper  64  toward the vertical, at the same time the piston  64   c  and the cylinder  64   a  move relatively. Therein, the piston  64   c  and the cylinder  64   a  undergo resistance while moving relative to each other, and therefore the turning speed of the first shaft  65 , and in turn the moving speed of the first and second arms  68  and  71 , is damped. 
     One each of the rear wheel assemblies  5  is provided on either of the right and left sides of the cart  1 . As indicated in FIGS. 5-10, each rear wheel assembly  5  includes a stationary plate (fixed member)  51 , a wheel mount  52 , a fifth shaft  53  (wheel support device), a tire  54  (wheel) and a lock mechanism  9 . 
     The stationary plate  51  is fastened to the rear portion of the cart body  2 . The wheel mount  52  chiefly comprises a horizontal plate  52   a , a first flanking plate  52   b  and a second flanking plate  52   c.    
     The horizontal plate  52   a  is disposed beneath the stationary plate  51 , wherein it is supported to be pivotable against the stationary plate  51  around a vertical shaft. The first flanking plate  52   b  extends downward from the outer edge of the horizontal plate  52   a  (the facing side in the FIG. 6 view), and the second flanking plate  52   c  extends downward from the inner edge of the horizontal plate  52   a  (the side opposite in the FIG. 6 view—shown in the cutaway). The lower ends of the first and second flanking plates  52   b  and  52   c  are provided respectively with round apertures, in which the fifth shaft  53  is rotatably supported. 
     The lock mechanism  9  is configured to restrict the wheel mount  52  from pivoting relative to the stationary plate  51  when the cart  1  is traveling in the advancing direction D 1 , and to release the restriction on the wheel mount  52  from pivoting relative to the stationary plate  51  when the cart  1  is moves opposite to the advancing direction D 1 . The lock mechanism  9  has an engage plate (engagement member)  91 , a stop  92  and a stop retainer  94 . 
     The engage plate  91  is supported to be non-rotatable on the fixed portion  51 . An arcuate notch  91   a  is formed in the rear edge of the engage plate  91 , as shown in FIGS.  5  and  7 - 9 . 
     The stop  92  is composed of columnar lock, retained and contact portions  92   a ,  92   b  and  92   c , respectively, which are coaxial and of different diameters. The lock portion  92   a  penetrates oblong hole  93   a  (described later). Therein, the lock portion  92   a  can be caught into the notch  91   a  (the state in FIGS.  5  and  6 ), into locking engagement with the engage plate  91 . The retained portion  92   b  is held within the stop retainer  94  (also described later), and is of larger diameter than, and is disposed between, the lock and contact portions  92   a  and  92   c . The contact portion  92   c  extends downward from the retained portion  92   b , and its lower surface in contact with the tire  54 . 
     The stop holding member (stop retainer)  94  is attached to the lower surface of the horizontal plate  52   a  of the wheel mount  52 , and holds the lower surface of the retained portion  92   b  of the stop  92 . An oblong hole  94   a  is formed in the stop retainer  94 , and the contact portion  92   c  of the stop  92  penetrates the oblong hole  94   a . The oblong hole  94   a  is an opening lengthened in the rotational direction of the tire  54 —that is, in the direction orthogonal to the fifth shaft  53 —and its width is about equal to the diameter of the contact portion  92   c . Consequently, being that the contact portion  92   c  cannot move against the oblong aperture  94   a  in the direction along the fifth shaft  53 , the stop  92  cannot move against the stop retainer  94  and the wheel mount  52  in the direction along the fifth shaft  53 . Nevertheless, because the contact portion  92   c  is movable along the lengthwise direction of the oblong hole  94   a , the stop  92  can move just a predetermined distance along the rotational direction of the tire  54  (the direction orthogonal to the fifth shaft  53 ). 
     As shown in FIGS. 5,  7  and  8 , the above-mentioned oblong hole (stop holder)  93   a  is formed in the horizontal plate  52   a  of the wheel mount  52 . The oblong hole  93   a  is an opening lengthened in the rotational direction of the tire  54 —that is, in the direction orthogonal to the fifth shaft  53 . Because the lock portion  92   a  of the stop  92  penetrates the oblong hole  93   a , the stop  92  is essentially immobile in the direction against the wheel mount  52 , along the fifth shaft  53 . 
     As shown in FIGS. 5 and 6, the rear-wheel drop attenuator  8  primarily comprises second oil dampers  81 , third outer arms  82 , third inner arms  84  and third traction members  87 . 
     Each second oil damper  81  is composed chiefly of a cylinder  81   a , a cylinder-end joint  81   b , a piston  81   c  and a piston-end joint  81   d . The cylinder-end joint  81   b  is fixed to the lower end of the cylinder  81   a , and is rotatably coupled to a portion of the fifth shaft  53  outside the first flanking plate  52   b . One end of the piston  81   c  is fitted onto the piston-end joint  81   d , and is in pin engagement with the upper end of the third outer arm  82 . 
     One end of each third outer arm  82  is in pin engagement with the piston-end joint  81   d , and, as shown in FIG. 5, extends from there rearward (leftward in FIG. 5) of the rear wheel assembly  5 . The other end of the third outer arm  82  carries an end of a sixth shaft  86  (referring to FIG.  6 ). 
     Each third outer arm  82 , between either end (in a location toward its engagement with the piston-end joint  81   d ), is rotatably supported on the first flanking plate  52   b  by a pin  83 . Therefore, the second outer arm  82  is rotatable about the pin  83  as its center. 
     Each third inner arm  84 , as shown in FIG. 5, is rotatably supported on the second flanking plate  52   c  by a pin  85  in a location equivalent to the height position and back-and-forth position of the pin  83 . The other end of the third inner arm  84  carries an end of the sixth shaft  86 . 
     The sixth shaft  86  joins together the ends of third outer arm  82  and the third inner arm  84 , wherein it extends horizontally right/leftward. The central portion of the sixth shaft  86  is fitted with the third traction member  87 , which is made of rubber or the like. 
     As shown in FIG. 6, the third traction member  87  is positioned slightly higher than the lower end of the rear wheel assembly  5  when the front wheel assembly  5  is grounded on a floor surface. 
     The third outer arm  82  and the third inner arm  84  can travel from the situation indicated by solid lines in FIG. 6 to that indicated by dotted lines. This travel describes an arc that is approximately the specification slope of the escalator. In thus moving, the point of engagement of the third outer arm  82  and the piston-side joint  81   d  travels forward as well as downward. This inclines the second oil damper  81 , and at the same time the piston  81   c  and the cylinder  81   a  move relatively and are compressed. Therein, the piston  81   c  and the cylinder  81   a  undergo resistance while moving relative to each other, and therefore the travelling speed of the point of engagement of the third outer arm  82  and the piston-side joint  81   d , and in turn the moving speed of the third traction member  87 , is damped. 
     A description of the operation of the cart follows. 
     When the cart  1  is run straight, an operator (user) grips the handle  3  and pushes the entire cart  1  in the advancing direction D 1 . Doing so orients each rear wheel assembly  5  along the advancing direction D 1 , wherein, as shown in FIGS. 5,  6  and  7 , the front portion of the oblong hole  93   a  and the recess  91   a  coincide superficially. The contact portion  92   c , contacting the outer peripheral surface of the tire  54 , receives a force in accordance with rotation of the tire  54 , moving the stop  92  forward (in the advancing direction D 1 ), engaging the lock portion  92   a  of the stop  92  with the notch  91   a  of the engage plate  91 . Thereby, via the lock portion  92   a , the engage plate  91  and the horizontal plate  52   a  of the wheel mount  52  (referring to FIG. 5) are made mutually non-rotatable, such that the wheel mount  52  and the wheel  54  cannot turn relative to the stationary plate  51  fixed to the cart body  2 . In other words, in running the cart  1  straight, the orientation of the tire  54  is fixed by the lock mechanism  9 , securing the straight forwardness of the cart  1 . 
     When the user desires to move the cart  1  laterally (in directions orthogonal to or crossing the advancing direction D 1 ), the tire  54  fixed by the lock mechanism  9  from pivoting relative to the cart body  2  is released. Concretely, the user brings the cart  1  to a stop, and moves the cart  1  slightly in a direction opposite to the advancing direction D 1 . Doing so rotates the tire  54  reverse to the advancing direction D 1 , shifting the contact portion  92   c  of the stop  92  rearward in accordance with the rotation of the tire  54 , and bringing the lock portion  92   a  of the stop  92  out of the notch  91   a  in the engage plate  91  (FIGS. 8,  9  and  10 ). Accordingly, the rotational locking engagement of the stop  92  and the notch  91   a  in the engage plate  91 , mutually non-rotatable against the stationary plate  51 , is released. That is, the check on relative rotation between the wheel mount  52  and the stationary plate  51  is released, such that the orientation of the tire  54  with respect to the cart body  2  can be changed. Accordingly, by thereafter applying a lateral force to the cart  1 , the user can change the orientation of the tire  54 , as for example indicated by the dotted lines in FIG. 9, and move the cart  1  sideways. 
     A description of running the cart  1  on a descending escalator follows. 
     On a descending escalator, in the situation as shown in FIG. 11, when the front and rear wheel assemblies  4  and  5  are riding steps S 2  and S 4 , rotation of the rear wheel assemblies  5  is checked by operating a not-shown brake mechanism, which keeps the cart  1  from slipping back-and-forth. That is, in the situation shown in FIG. 11, the cart  1 , without dropping, is carried by the escalator. When the front and rear wheel assemblies  4  and  5  are riding on the middle portions tread-lengthwise of the steps S 2  and S 4  as shown in FIG. 11, the second traction member  75  is grounded on the frontward portion of the step S 4  on which the front wheel assembly  4  is riding, supplementing the check on back-and-forth shifting of the cart  1 . 
     In boarding a descending escalator wherein the front and rear wheel assemblies  4  and  5  are riding near the step-to-step breaks, when the escalator slopes, the cart  1  is brought into a situation as shown in FIG.  12 . The cart  1  thereupon begins to drop to steps S 6  and S 8  one step below, bringing about the situation as shown in FIG.  13 . Herein, at about the same time, the first and third traction members  73  and  87  initially gain traction on steps S 5  and S 7 , on which the front and rear wheel assemblies  4  and  5  had been riding. Then, with the first and third traction members  73  and  87  still adhesively in contact with the steps S 5  and S 7 , the cart  1  continues to drop, and the front and rear wheel assemblies  4  and  5  land one step below, on steps S 6  and S 8  (referring to FIG.  14 ). Nonetheless, whereupon the first and third traction members  73  and  87  have gained traction on the steps S 5  and S 7 , the speed of relative motion of the cart body  2  and the first and third traction members  73  and  87  is damped by the first and second oil dampers  64  and  81 , retarding the dropping speed of the cart  1 . Accordingly, an operator&#39;s uneasiness and apprehensiveness due to the cart  1  dropping on a descending escalator are ameliorated. Furthermore, because the impact is attenuated when the front and rear wheel assemblies  4  and  5  land one step below on steps S 6  and S 8 , tumbling and dropping of baggage loaded the cart  1  is held in check. 
     A description of running the cart  1  on an ascending escalator follows. 
     On an ascending escalator, in the situation as shown in FIG. 15, when the front and rear wheel assemblies  4  and  5  are riding steps Sll and S 12 , rotation of the rear wheel assemblies  5  is checked by operating the not-shown brake mechanism, which keeps the cart  1  from slipping back-and-forth. That is, in the situation shown in FIG. 15, the cart  1 , without dropping, is carried by the escalator. When the front and rear wheel assemblies  4  and  5  are riding on the middle portions tread-lengthwise of the steps S 11  and S 13  as shown in FIG. 15, the first and third traction members  73 ,  87  are grounded on the rearward portions of the steps S 11 , S 13  on which the front and rear wheel assemblies  4  and  5  are riding, supplementing the check on back-and-forth shifting of the cart  1 . 
     In boarding an ascending escalator wherein the front and rear wheel assemblies  4  and  5  are riding near the step-to-step breaks, when the escalator slopes, the cart  1  is brought into a situation as shown in FIG.  16 . The cart  1  thereupon begins to drop to steps S 16  and S 18  one step below, and as shown in FIG. 17 the second traction member  75  initially gains traction on step S 15 . At that time, moreover, the third traction member  87  lands one step below on step S 18 . Then, as shown in FIG. 18, the front and rear wheel assemblies  4  and  5  land one step below, on steps S 16  and S 18 . Nonetheless, whereupon the second traction member  75  has gained traction, the speed of relative motion of the cart body  2  and the second traction member  75  is damped by the first oil damper  64 , retarding the dropping speed of the cart  1 . Also, the falling speed of the rear wheel assemblies  5  and the rear portion of the cart  1  is attenuated by the second oil damper  81 . Accordingly, an operator&#39;s uneasiness and apprehensiveness due to the cart  1  dropping on an ascending escalator are ameliorated; further, tumbling and dropping of baggage loaded the cart  1  is held in check. 
     Various details of the present invention may be changed without departing from its spirit nor its scope. 
     Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.