Abstract:
A utility cart includes an auxiliary swivel caster wheel assembly, a locking mechanism, and a trigger mechanism for causing the locking mechanism to releasably lock the auxiliary swivel caster wheel assembly. The auxiliary swivel caster wheel assembly is unlocked to enable the auxiliary swivel caster wheel to rotate about a vertical axis for improved maneuverability in small areas, and is locked to hold the auxiliary swivel caster wheel in a predetermined position for improved steering as the cart is moved from one location to another. The trigger mechanism is disposed on a steering handle to enable dynamic actuation of the locking mechanism while the cart is in motion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an auxiliary swivel caster wheel assembly and a caster direction-locking mechanism for a mobile utility cart, and more particularly to such a wheel assembly and locking mechanism for a mobile utility cart commonly called a “medical emergency crash cart” or simply a “crash cart”, for medical emergency use in hospitals and other medical institutions. The auxiliary swivel caster wheel assembly and direction-locking caster mechanism in accordance with the present invention provide the crash cart with improved high speed stability and maneuverability. A trigger mechanism for selectively locking and unlocking the direction-locking caster mechanism also is included. 
     2. Description of Related Art 
     A medical emergency crash cart commonly contains medical equipment, instruments, and supplies that may be required while responding to medical emergencies, particularly for medical procedures practiced in cases of cardiac emergencies. However, the crash cart may be equipped for any type of medical emergency. The crash cart generally includes a housing having a plurality of drawers, shelves, and/or compartments for storing medical equipment and supplies such as syringes and drugs. The housing is supported by a plurality of wheels or casters so that it may be moved rapidly from its place of storage to a location of a medical emergency. To provide maximum efficiency during a medical emergency, a crash cart must therefore provide both agile and stable mobility. 
     One drawback of many known crash carts is a lack of stability during high speed travel. First, as a crash cart must be able to maneuver quickly in small areas of patients&#39; or hospital emergency rooms, it is desirable to support the housing on swivel casters. Second, as medical equipment, instruments, and supplies are expensive, hospitals may maintain only a limited number of crash carts (e.g. one crash cart per floor or station). Therefore, when a medical emergency occurs, a crash cart operator must rush the cart through the hospital corridors often over relatively long distances to a patient. However, the swivel casters may cause the cart to be difficult to steer at high speeds particularly when an attempt is made to change the direction of movement, for example, by going around corners in corridors or turning into a patient&#39;s room. Therefore, the crash cart operator must either reduce his speed through the corridors or risk overturning the cart. The risk of overturning increases when the operator must negotiate the cart around a corner, as swivel casters do not provide a firm pivot about which to turn but rather permit inertia of the cart to cause it to tend to continue to move in its original direction. Alternatively, a crash cart may be operated by two persons. However, this is less efficient and may, in fact, not be possible during a given emergency. 
     U.S. Pat. No. 4,790,610 (Welch et al.), U.S. Pat. No. 4,875,696 (Welch et al.), and U.S. Pat. No. 7,370,867 (Olson et al.) disclose mechanisms for selectively locking swivel caster wheel assemblies in predetermined positions. However, while the mechanisms disclosed in these patents have many advantages, they are not well suited for dynamic actuation while a cart is in motion. For example, actuators for these mechanisms may be located on a side of a cart and/or may be positioned for actuation by an operator&#39;s foot, or may be otherwise inconvenient for the operator to actuate while the cart is in motion. 
     In addition, U.S. Pat. No. 6,725,956 (Lemire) discloses a hospital bed having four wheels in contact with a floor surface, and a motorized assembly that is employed to raise and lower an auxiliary or fifth wheel away from and toward the floor. When the fifth wheel is raised, the hospital bed functions as a conventional hospital bed. When the fifth wheel is lowered, it contacts the floor surface and the motorized assembly causes the fifth wheel to rotate, which propels the hospital bed. The fifth wheel is held at a predetermined position relative to a frame of the hospital bed, thus, the fifth wheel must be raised when maneuvering the hospital bed in a small area, such as a patient&#39;s room. However, the fifth wheel cannot be raised and lowered quickly. Accordingly, the fifth wheel disclosed in the Levine Patent is not well-suited for use in emergency situations. 
     For these and other reasons, the crash carts and related mechanisms for improving mobility of wheeled apparatuses of the prior art are not entirely satisfactory. A need exists for an improved crash cart and related mechanisms for providing even greater high speed stability and maneuverability. 
     SUMMARY OF THE INVENTION 
     Generally speaking, the present invention will be referred to as a “cart,” which is highly maneuverable and which may incorporate an enclosed cabinet for storing items, such as medical supplies used in responding to medical emergencies. However, the present invention may be used in conjunction with a variety of wheeled apparatus, including stretchers, medical storage carts, and hospital beds, for example, as well as other utility carts that have general application outside of the medical field. Accordingly, the present invention is not limited to crash or other medical carts, but may be used in conjunction with any wheeled structure that can benefit from improved maneuverability and stability. 
     In one embodiment, the present invention is directed to a cart having a first end and a second end. The cart includes at least four swivel casters supporting the cart. A first two of the swivel casters are adjacent each other and support the cart in the region of the first end, and a second two of the swivel casters are adjacent each other and support the cart in the region of the second end. Each swivel caster includes a wheel rotatable about a horizontal axis, and is mounted with the cart for swiveling movement about a generally vertical axis. An auxiliary swivel caster assembly also supports the cart. The auxiliary swivel caster assembly includes a wheel rotatable about a horizontal axis, and is mounted with said cart for swiveling movement about a generally vertical axis. The cart also includes locking means selectably operable to lock the auxiliary swivel caster assembly against swiveling movement when the wheel of the auxiliary swivel caster assembly swivels to a predetermined position. Further, the cart includes actuator means for actuating the locking means to selectably engage and disengage the auxiliary swivel caster assembly. 
     In another embodiment, the present invention is directed to cart including a base portion. A pair of leading end swivel casters support the base portion, each of the pair of leading end swivel casters includes a rotatable wheel. A pair of trailing end swivel casters supporting the base portion, each of the pair of trailing end swivel casters includes a rotatable wheel. An auxiliary swivel caster assembly also supports the base portion, the auxiliary swivel caster assembly swivels about a substantially vertically extending axis, and includes a rotatable wheel. The cart also includes means for urging the wheel of the auxiliary swivel caster assembly toward a floor supporting the cart. A locking mechanism engages the auxiliary swivel caster assembly in a locked position to prevent swivel action thereof, when the auxiliary swivel caster assembly is rotated about its axis to a predetermined position. Further, the cart includes means for biasing the locking mechanism toward an unlocked position to permit swivel action of the auxiliary swivel caster assembly. An actuator is operable when actuated to move the locking mechanism from the unlocked position, and when the actuator is deactivated to permit the locking mechanism to be biased by the biasing means toward the unlocked position. The cart also includes means located on said cart for operating said actuator with a user&#39;s hand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view, taken from the front top right, of a preferred embodiment of a crash cart in accordance with the present invention. 
         FIG. 2  is a perspective view taken from the front of the crash cart illustrated in  FIG. 1 . 
         FIG. 3  is a perspective view taken from the bottom of the crash cart illustrated in  FIG. 1 . 
         FIG. 4  is a perspective view taken from the front of an auxiliary swivel caster wheel assembly in accordance with an embodiment of the present invention. 
         FIG. 5  is a side view of the auxiliary swivel caster wheel assembly illustrated in  FIG. 4 . 
         FIG. 6  is a top view of the auxiliary swivel caster wheel assembly illustrated in  FIG. 4 . 
         FIG. 7  is a bottom view of a caster direction-locking mechanism in accordance with an embodiment of the present invention and the auxiliary swivel caster assembly wheel assembly illustrated in  FIGS. 4 through 6 , shown in an unlocked position. 
         FIG. 8  is a top view of the caster direction-locking mechanism and the auxiliary swivel caster wheel assembly illustrated in  FIG. 7 . 
         FIG. 9  is a perspective view taken from the bottom of the caster direction-locking mechanism and the auxiliary swivel caster wheel assembly illustrated in  FIG. 7 . 
         FIG. 10  is a vertical cross-sectional view of the caster direction-locking mechanism and the auxiliary swivel caster wheel assembly illustrated in  FIG. 8 , partly shown in phantom, as viewed from plane  10  in the direction of the arrows shown in  FIG. 8 . 
         FIG. 11  is an exploded view of a portion of the caster direction-locking mechanism shown in  FIGS. 7 through 10 . 
         FIG. 12  is a top view the crash cart shown in  FIG. 1 . 
         FIG. 13  is a top view of an upper member and a handle of the crash cart shown in  FIG. 1 . 
         FIG. 14  is a bottom view of the upper member and the handle shown in  FIG. 13 . 
         FIG. 15  is a bottom view of a trigger mechanism according to an embodiment of the present invention. 
         FIG. 16  is a top view of the trigger mechanism shown in  FIG. 15 . 
         FIG. 17  is a bottom view of the upper member, the handle, and the trigger mechanism of the crash cart shown in  FIG. 1 . 
         FIG. 18  is a perspective view of the caster direction-locking mechanism and the auxiliary swivel caster wheel assembly illustrated in  FIGS. 7 through 10 , shown in a locked position. 
         FIG. 19  is a top view of the caster direction-locking mechanism shown in  FIG. 18 . 
         FIG. 20  is an exploded view of a portion of a caster direction-locking mechanism according to a second embodiment of the present invention. 
         FIG. 21  is a top view an auxiliary swivel caster wheel assembly according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Initially, the principal features of the present invention will be described generally in order to provide an overview of its various aspects. Then those features will be described in detail. 
       FIGS. 1 through 3  show one embodiment of a crash cart  100  according to the present invention. As shown in those figures, the crash cart  100  has a substantially rectangular horizontal cross-section or foot print as defined by a base portion  102 . The base portion  102  is comprised of four horizontal base members  104   a ,  104   b ,  104   c , and  104   d . Four vertical support members  106   a ,  106   b ,  106   c , and  106   d  are attached to or near respective corners of the base portion  102 . Side panels (not shown) may be attached to the vertical support members  106   a ,  106   b ,  106   c , and  106   d  to form an enclosure in which shelves and/or drawers are provided for holding medical supplies. The base portion  102  and vertical support members  106   a ,  106   b ,  106   c , and  106   d  could be integrally formed, or constructed according to other known techniques without departing from the scope of the invention. 
     An upper member  108  is attached to upper ends of the vertical support members  106   a ,  106   b ,  106   c , and  106   d , for example using a plurality of fasteners and screws (not shown). The upper member  108  has a recessed portion  108   a  for holding medical supplies. In addition, the upper member  108  includes a handle  112  for steering the cart  100 . A trigger mechanism  114  is slidably attached to the handle  112 , as will be described below. The trigger mechanism  114  preferably is disposed near the handle  112  so that it can be actuated while a cart operator (not shown) is steering the cart  100 . In the exemplary embodiment, the upper member  108  and the handle  112  are integrally formed. However, in other embodiments the upper member  108  and the handle  112  are discrete components attached according to known techniques. 
     Four conventional swivel caster wheel assemblies  116   a ,  116   b ,  116   c , and  116   d  are provided at or near respective corners of the base portion  102 . In addition, an auxiliary wheel support member  118  is attached to the base portion  102 , generally toward the rear end of the cart  100 , i.e., the end where the handle  112  is provided. More specifically, the wheel support member  118  is formed with a lower plate  118   a , which spans the distance between front and rear base members  104   d  and  104   b , and opposing upstanding flanges  118   b  each at one extreme end of the lower plate  118   a  thereby to be outside of the base members  104   d  and  104   b . Each flange  118   b  is attached to the adjacent base member  104   d  and  104   b  by a pivot pin  119  so that a rear edge of the support member can pivot toward and away from a supporting floor. 
     Auxiliary Swivel Caster Wheel Assembly 
     First Embodiment 
     An auxiliary swivel caster wheel assembly  120  is attached to the auxiliary wheel support member  118 . The auxiliary swivel caster wheel assembly  120  may be attached to the auxiliary wheel support member  118  in a center portion thereof, i.e., midway between horizontal base members  104   b  and  104   d . Alternatively, the auxiliary swivel caster wheel assembly  120  may be biased or offset from the center portion of the auxiliary wheel support member  118 . That is, the auxiliary swivel caster wheel assembly  120  may be attached to the auxiliary wheel support member  118  at a position that is closer to one of the horizontal base members  104   b  and  104   d  than to the other of the horizontal base members  104   b  and  104   d.    
     The auxiliary swivel caster wheel assembly  120  is attached to the auxiliary wheel support member  118  using a plurality of nuts and bolts (not labeled), for example. As will be described in detail below, a caster direction-locking mechanism  122  also is attached to the auxiliary wheel support member  118  to releasably engage the auxiliary swivel caster wheel assembly  120  to permit or prevent rotation of the auxiliary swivel caster wheel assembly  120 . 
     An embodiment of the auxiliary swivel caster wheel assembly  120  of the present invention is described with reference to  FIGS. 4 through 6 . A swivel mount  124  is rigidly attached to a mounting plate  126 , for example, by a welding process. The mounting plate  126  includes a plurality of apertures  126   a  formed therein, through which a plurality of bolts (not shown in  FIGS. 4 through 6 ) are inserted to secure the auxiliary swivel caster wheel assembly  120  to the auxiliary wheel support member  118 . 
     A generally inverted U-shaped horn  128  is rotatably mounted to the swivel mount  124 . More particularly, a post  130  is provided within the swivel mount  124  and bearings (not shown) are disposed about the post  130 . The bearings (not shown) enable the horn  128  to rotate or swivel freely about the post  130 , with a full 360° of rotational freedom, as is customary with conventional swivel caster wheels. The post  130  serves as a vertical axis of rotation for the horn  128 . 
     The horn  128  includes a top portion  128   a , a first leg portion  128   b , a second leg portion  128   c , and a notch  128   d  formed in the top portion  128   a . An aperture (not shown) is formed in each of the first leg portion  128   b  and the second leg portion  128   c  of the horn  128 . A threaded end of a bolt  132  is inserted though the aperture of the second leg portion  128   c , an aperture (not shown) of a wheel  136 , and the aperture of the first leg portion  128   b . A nut  134  is secured to the threaded portion of the bolt  132 . The bolt  132  serves as a horizontal axis of rotation for the wheel  136 . Bearings (not shown) disposed within the wheel  136  enable the wheel  136  to rotate about the bolt  132 , with a full 360° of rotational freedom. 
     As shown in  FIG. 2 , the wheel support member  118  is urged to rotate in the clockwise direction by a pair of comparison springs  121  each interposed between the top of the lower plate  118   a  and a bottom surface of one of the base members  104   d  and  104   b . In this way the wheel  136  of the assembly  120  is always urged toward a supporting floor. Rotation of the support member  118  as described is limited by interference of forward edge  118   c  with the base members  104   d  and  104   b.    
     As best illustrated in  FIG. 6 , as noted above the top portion  128   a  of the horn  128  has a notch  128   d  formed therein. As will be explained below in detail, a locking member  152  of the caster direction-locking mechanism  122  releasably engages the notch  128   d  to selectively prevent or permit rotation of the horn  128  about the post  130  of the auxiliary swivel caster wheel assembly  120 . When the notch is engaged to prevent rotation of the horn  128 , the wheel  136  is constrained to rotate with its axis substantially parallel to the front of the cart. 
     Caster Direction-Locking Mechanism 
     First Embodiment 
     An embodiment of the caster direction-locking mechanism  122  of the present invention is described with reference to  FIGS. 7 through 19 . A mounting plate  140  is provided to attach the caster direction-locking mechanism  122  to the auxiliary wheel support member  118 . The mounting plate  140  includes three apertures  140   a ,  140   b , and  140   c  formed therein, as shown in  FIG. 11 . A threaded end of a bolt (not labeled) is inserted into each of the apertures  140   a  and  140   b , and through corresponding apertures (not shown) formed in the auxiliary wheel support member  118 . A nut (not labeled) is securely attached to the threaded end of each of the bolts, thereby securing the mounting plate  140  to the auxiliary wheel support member  118 . 
     The caster direction-locking mechanism  122  is pivotally attached to the mounting plate  140  using a shoulder screw  146  and a nut  148 . More particularly, as best shown  FIG. 11 , a threaded end of the shoulder screw  146  is inserted through an aperture of a first washer  149   a , an aperture  142   a  formed in a floating pin bracket  142 , an aperture of a spacer  158 , an aperture of a torsion spring  160 , an aperture  144   a  of a swivel lock bracket  144 , the aperture  140   c  of the mounting plate  140 , and an aperture of a second washer  149   b . A nut  148  is securely attached to the threaded end of the shoulder screw  146  thereby securing the shoulder screw  146 , and thus, the caster direction-locking mechanism  122 , to the mounting plate  140 . 
     The floating pin bracket  142  also includes an aperture  142   b  formed therein. A first end of a locking member  152  is inserted through the aperture  142   b  of the floating pin bracket  142 . A nut  153  is secured to threads formed on a portion of the locking member  152 . As will be explained in detail below, actuation of the caster direction-locking mechanism  122  causes the locking member  152  to releasably engage the notch  128   d  of the top portion  128   a  of the horn  128  of the auxiliary swivel caster wheel assembly  120 , when the notch  128   d  becomes aligned with the locking member  152 . 
     The floating pin bracket  142  also includes a first flange  142   c  and a second flange  142   d . When the caster direction-locking mechanism  122  is assembled, a first end  160   a  of the torsion spring  160  exerts a force on the first flange  142   c  of the floating pin bracket  142 . Similarly, the swivel lock bracket  144  includes a first flange  144   c  and a second flange  144   d . When the caster direction-locking mechanism  122  is assembled, a second end  160   b  of the torsion spring  160  exerts a force on the first flange  144   c  of the swivel lock bracket  144 . 
     When the caster direction-locking mechanism  122  is assembled, the spacer  158  is disposed about a portion of the shoulder screw  146  having no threads thereon. The spacer  158  preferably is formed from nylon and permits the torsion spring  160  to rotate substantially unimpeded about the unthreaded portion of the shoulder screw  146 . 
     The arrangement of the shoulder screw  146 , the spacer  158 , the torsion spring  160 , the first flange  142   c  of the floating pin bracket  142 , and the first flange  144   c  of the swivel lock bracket  144  cause the floating pin bracket  142  to be urged or biased towards the swivel lock bracket  144  until the second flange  142   d  of the floating pin bracket  142  contacts the second flange  144   d  of the swivel lock bracket  144 . As will be described below, the mentioned arrangement causes the locking member  152  to engage smoothly the notch  128   d  of the top portion  128   a  of the horn  128 , when the caster direction-locking mechanism  122  is activated. 
     As shown in  FIGS. 7-10 ,  18 , and  19 , a cable  154  is provided within a cable housing  156 . The cable  154  and the cable housing  156  in conjunction with a trigger mechanism  114 , cause the caster direction-locking mechanism  122  to rotate about the shoulder screw  146  so as to releasably engage the locking member  152  in notch  128   d  the top portion  128   a  of the horn  128 . 
     As shown in  FIG. 11 , the swivel lock bracket  144  includes a second aperture  144   b  formed in the second flange  144   d . As shown in  FIG. 8 , for example, the first end of a barrel adjuster bolt  162  is inserted through the second aperture  144   b  of the swivel lock bracket  144 , and a nut (not shown) is secured thereto. A barrel adjuster nut  164  is positioned on an opposing second end of the barrel adjuster bolt  162  and advanced until it contacts the second flange  144   d , as shown in  FIG. 8 , for example. A first end of the cable housing  156  is attached to the second end of the barrel adjuster bolt  162 . The barrel adjuster bolt  162  enables a distance between the second flange  144   d  of the swivel lock bracket  144  and the first end of the cable housing  156  to be adjusted. The barrel adjuster bolt  162  and barrel adjuster nut  164  are adjusted in a manner that is similar to adjusting a cable of a bicycle caliper brake system. 
     As shown in  FIG. 8 , a first end of the cable  154  is inserted through the barrel adjuster bolt  162  and a tension spring  150  prior to being attached to the auxiliary wheel support member  118 . A bolt  166  includes an aperture (not shown) formed in a threaded portion thereof. The bolt  166  is inserted through an aperture (not shown) of the auxiliary wheel support member  118 , and the first end of the cable  154  is inserted through another aperture (not shown) of the auxiliary wheel support member  118  and through the aperture of the bolt  166 . A nut  168  is securely attached to the bolt  166  thereby clamping the first end of the cable  154  to the auxiliary wheel support member  118 . 
     Trigger Mechanism 
     As shown in  FIG. 14 , a bottom side of the handle  112  includes a first flange  112   a , a second flange  112   b , and apertures  112   c  and  112   d . As shown in  FIG. 16 , a top side of the trigger mechanism  114  includes a notch  114   a , a first side member  114   b  that forms a first groove, a second side member  114   c  that forms a second groove, and elongated apertures  114   d  and  114   e.    
     Attachment of the cable  154  and the trigger mechanism  114  to the handle  112  is described with reference to  FIGS. 14 through 17 . A cable stop (not shown) is secured to the second end of the cable  154 . The cable stop is similar to cable stops that are attached to conventional bicycle brake cable wires. The second end of the cable  154  is placed in the notch  114   a  such that the cable stop is disposed within the trigger mechanism  114 . 
     The top side of the trigger mechanism  114  is placed in contact with the bottom side of the upper member  108  such that the first groove formed by the first side member  114   b  of the trigger mechanism  114  is disposed about the second flange  112   b  of the handle  112 , and the second groove formed by the second side member  114   c  of the trigger mechanism  114  is disposed about the first flange  112   a  of the handle  112 . A screw (not shown) is inserted through each the elongated apertures  114   d  and  114   e  of the trigger mechanism  114 , and these screws are secured within the apertures  112   c  and  112   d  of the handle  112 , respectively. The trigger mechanism is now slidably attached to the handle  112 . 
     Accordingly, the first ends of the cable  154  and the cable housing  156  are connected to the locking mechanism  122  and the second ends of the cable  154  and the cable housing  156  are connected to the trigger mechanism  114 . Portions of the cable  154  and the cable housing  156  between the first ends and the second ends are disposed within the cart  100 . For example, such portions are housed in a hollow, center portion of a panel (not shown) that is attached to the trailing end of the cart, i.e., the end where the handle  112  is provided. 
     Actuation of the Caster Direction-Locking Mechanism 
     As noted above, the wheel  136  of the caster assembly  120  is always urged toward a supporting floor by springs  121 . Further, when the trigger mechanism  114  is not actuated by a user, a biasing force of the tension spring  150  urges the swivel lock bracket  144  away from the auxiliary swivel caster wheel assembly  120 , as shown in  FIGS. 7 through 10 . In addition, the second flange  144   d  of the swivel lock bracket  144  exerts a force on the second flange  142   d  of the floating pin bracket  142 , which causes the floating pin bracket  142  also to be urged away from the auxiliary swivel caster wheel assembly  120 . When the swivel lock bracket  144  and the floating pin bracket  144  are urged away from the auxiliary swivel caster wheel assembly  120  via the tension spring  150 , the locking member  152  does not engage the notch  128   d  of the upper portion  128   a  of the horn  128 , as shown in  FIG. 9 . Accordingly, when the trigger mechanism  114  is not actuated by a user, the horn  128 , and thus the wheel  136 , are permitted to rotate freely about the post  130  of the auxiliary swivel caster wheel assembly  120 . Even though the wheel  136  is in contact with the floor, the cart may be moved as all five wheels may swivel. 
     When a user pulls the trigger mechanism  114  in a direction toward the user, the notch  114   a  of the trigger mechanism  114  exerts a force on the cable stop attached to the second end of the cable  154  thereby causing the second end of the cable  154  to move in the direction toward the user, which activates the caster direction-locking mechanism  122 . When the user releases the trigger mechanism  114 , the caster direction-locking mechanism  122  causes the cable stop attached to the second end of the cable  154  to exert a force on notch  114   a  of the trigger mechanism  114  in a direction away from the user, which causes the trigger mechanism  114  to return to its original position on the handle  112 . 
     When a user actuates the trigger mechanism  114 , the first end of the cable housing  156  is urged toward the auxiliary swivel caster wheel assembly  120 . Because the first end of the cable housing  156  is secured to the second flange  144   d  of the swivel lock bracket  144  via the barrel adjuster bolt  162 , actuation of the trigger mechanism  114  causes the swivel lock bracket  144  to be urged toward the auxiliary swivel caster wheel assembly  120 . As described above, the torsion spring  160  urges the floating pin bracket  142  toward the swivel lock bracket  144 . Accordingly, when the swivel lock bracket  144  is urged toward the auxiliary swivel caster wheel assembly  120  by actuation of the trigger mechanism  114 , the floating pin bracket  142  also is urged toward the auxiliary swivel caster wheel assembly  120 . 
     If the notch  128   d  is not aligned with the locking member  152  when the trigger mechanism  114  is actuated, the top portion of the  128   a  of the horn  128  will contact the locking member  152  and inhibit the floating pin bracket  142  from meeting the swivel lock bracket  144 . As the cart  100  is moved, the horn  128  rotates about the post  130  and the notch  128   d  of the horn  128  becomes aligned with the locking member  152  of the floating pin bracket  142 . The biasing force of the torsion spring  160  causes the locking member  152  of the floating pin bracket  142  to engage the notch  128   d , when the notch  128  becomes aligned with the locking member  152 , as shown in  FIG. 18 . As shown in  FIG. 6 , the upper portion  128   a  has a round shape which facilitates engagement of the locking member  152  into the notch  128   d  as the horn  128  rotates. The torsion spring  160  enables the floating pin bracket  142  to be spaced apart from the swivel lock bracket  144  as the horn  128  rotates to a predetermined position where the locking member  152  and the notch  128   d  are aligned. 
     Engagement of the locking member  152  into the notch  128   d  prevents the horn  128  from rotating about the post  130  of the auxiliary swivel caster wheel assembly  120 . The notch  128   d  is disposed on the horn  128  such that the wheel  136  of the auxiliary swivel caster wheel assembly  120  is held in a predetermined position, which is preferably substantially parallel to horizontal base members  104   b  and  104   d , when the locking member  152  engages the notch  128   d . Accordingly, when a user actuates the trigger mechanism  114 , the horn  128 , and thus the wheel  136 , are prevented from rotating about the post  120 , thereby providing a firm pivot for steering and maneuvering the cart  100 . 
     For example, if a user actuates the trigger mechanism  114  just before attempting to steer the cart  100  around a corner, the fixed position of the wheel  136  of the auxiliary swivel caster wheel assembly  120  provides a firm pivot that enables the cart  100  to round the corner without overturning and without the user otherwise loosing control of the cart  100 . The user would likely release the trigger mechanism  114  when maneuvering the cart  100  in a patient&#39;s room, which enables the tension spring  150  to cause the locking member  152  to disengage from the notch  128   d , thereby permitting the horn  128 , and thus the wheel  136 , to rotate freely about the post  130 . 
     The above-described arrangement of the floating pin bracket  142  and the notch  128   d , advantageously prevents the locking member  152  from causing the horn  128  to stop rotating in any position other than a position in which the locking member  152  is aligned with the notch  128   d . That is, if the locking member  152  were attached directly to the swivel lock bracket  144 , actuation of the trigger mechanism  114  would likely cause the horn  128  to stop rotating when the horn  128  is positioned at a random orientation, which would degrade steering and maneuverability of the cart  100 . 
     Caster Direction-Locking Mechanism 
     Second Embodiment 
       FIG. 20  illustrates an exploded view of a second embodiment of a caster direction-locking mechanism  1122  of the present invention. The caster direction-locking mechanism  1122  operates in a similar fashion to the caster direction-locking mechanism  122  described above. 
     The caster direction-locking mechanism  1122  is pivotally attached to the mounting plate  140  using a shoulder screw  1146   a  and a first nut  1148   a . More particularly, a threaded end of the shoulder screw  1146   a  is inserted through an aperture of a first washer  1149   a , an aperture of a first thrust bearing  1170   a , an aperture  1142   a  formed in a floating pin bracket  1142 , an aperture of a second thrust bearing  1170   b , an aperture  1144   a  of a swivel lock bracket  1144 , the aperture  140   c  of the mounting plate  140 , and an aperture of a second washer  1149   b . The first nut  148   a  is securely attached to the threaded end of the first shoulder screw  1146   a  thereby securing the first shoulder screw  1146   a , and thus the caster direction-locking mechanism  1122 , to the mounting plate  140 . The first thrust bearing  1170   a  and the second thrust bearing  1170   b  enable the floating pin bracket  1142  to pivot freely about the first shoulder screw  1146   a.    
     A threaded end of a second shoulder screw  1146   b  is inserted into an aperture of a bearing assembly  1172 , an aperture of a third washer  1149   c , an aperture  1142   b  of the floating pin bracket  1142 , and an aperture of a fourth washer  1149   d . A second nut  1148   b  is secured to the threaded end of the second shoulder screw  1146   b . The bearing assembly  1172  includes an outer portion  1172   a  and an inner portion  1172   b , which are separated by a plurality of ball bearings (not illustrated). When the bearing assembly  1170  is secured to the floating pin bracket  1142 , the outer portion  1172   a  is enabled to rotate freely about a vertical axis, i.e., the second shoulder screw  1146   b.    
     A tension spring  1160  is employed to urge the floating pin bracket  1142  toward the swivel lock bracket  1144 . More particularly, a first end  1160   a  of the tension spring  1160  is inserted into an aperture  1142   c  formed through the floating pin bracket  1142 , which secures the tension spring  1160  to the floating pin bracket  1142 . A second end  1160   b  of the tension spring  1160  is inserted into an aperture  1144   e  formed through the swivel lock bracket  1144 , which secures the tension spring  1160  to the swivel lock bracket  1144 . 
     The barrel adjuster bolt  162  is secured to an aperture  1144   b  formed in a flange  1144   d  of the swivel lock bracket  1144 . The first end of the cable  154  is inserted through the barrel adjuster bolt  162  prior to being attached to the auxiliary wheel support member  118 , as described above for the caster direction-locking mechanism  122 . Accordingly, actuation of the trigger mechanism  114  causes the swivel lock bracket  1144  to move toward the auxiliary wheel support member  118 , as described above for the caster direction-locking mechanism  122 . 
     Auxiliary Swivel Caster Wheel Assembly 
     Second Embodiment 
       FIG. 21  illustrates a top view of a second embodiment of an auxiliary swivel caster wheel assembly  1120  of the present invention. The swivel caster wheel assembly  1120  operates in a similar fashion to the caster direction-locking mechanism  120  described above. The swivel caster wheel assembly  1120  includes a horn  1128  having a top portion  1128   a  that has a notch  1128   d  formed therethrough. The notch  1128   d  of the swivel caster wheel assembly  1120  shown in  FIG. 21  is deeper and wider than the notch  128   d  of the swivel caster wheel assembly  120  shown in  FIG. 6 . The shape of the notch  1128   d  enables the outer portion  1172   a  of the bearing assembly  1172  to engage the notch  1128   d , when the trigger mechanism  114  is actuated. 
     As described above, the outer portion  1172   a  of the bearing assembly  1172  is enabled to rotate freely about the second shoulder screw  1146   b . When the trigger mechanism  114  is actuated, the swivel lock bracket  1144  is urged toward the auxiliary swivel caster wheel assembly  1120 . The tension spring  1160  enables the floating pin bracket  1142  to be spaced apart from the swivel lock bracket  1144  as the horn  1128  rotates to a predetermined position. The tension spring  1160  urges the floating pin bracket  1142  toward the swivel lock bracket  1144  as the horn  1128  rotates to the predetermined position, which causes the outer portion  1172   a  of the bearing assembly  1172  to contact the curved top portion  1128   a  of the horn  1128  and rotate, as the horn  1128  rotates to the predetermined position. When the bearing assembly  1172  becomes aligned with the notch  1128   d  at the predetermined position, the tension spring  1160  causes the bearing assembly  1172  to engage the notch  1128   d  of the horn  1128 , which prevents the swivel caster wheel assembly  1120  from rotating about its vertical axis. The arrangement described above advantageously enables the bearing assembly  1172  of the caster direction-locking mechanism  1122  to engage smoothly the notch  1128   d  of the horn  1128  of the swivel caster wheel assembly  1120 . 
     While the present invention has been described with respect to what is presently considered to be the preferred embodiments, the present invention is not limited to the disclosed embodiments. Rather, the present invention covers various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the appended claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.