Abstract:
A steering mechanism is provided for tandem wheeled vehicles. The steering mechanism employs casters that are capable of swivelling. The casters are attached to a base member and a pair of resilient members is used to provide control over the degree of swivel of the casters. When turning, the caster rotates in the direction of turn and is restricted by the resilient members. The degree of rotation which the caster is allowed depends on the resilience of the resilient members and the force being applied to motivate the turn. A skateboard is also provided which incorporates the steering mechanism.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to turning mechanisms for wheeled vehicles. The invention is specifically concerned with those turning mechanisms capable of being adapted to tandem wheeled vehicles. 
     Many attempts have been made in the past to incorporate turning capabilities in vehicles equipped with tandem wheels. In general, vehicles equipped with tandem wheels are incapable of turning while all the wheels are on the ground. In-line roller skates, for example, suffer from this inconvenience. Typical in-line roller skates employ an arrangement in which three to five wheels are placed in tandem. One of the biggest drawbacks of the in-line roller skate is that the operator is incapable of making right or left turns during single foot skating. Skateboards typically overcome this problem by employing a plurality of suspension frames which carry a wheel on either side, Turning is subsequently accomplished by movement of the suspension frame and not the wheels themselves. A variety of spring and tension assemblies have been employed by the prior art to control the turning of wheels in vehicles where the wheels are in tandem, but these devices are often complicated and difficult to manufacture economically. Accordingly, a simple and inexpensive turning mechanism would be beneficial for tandem wheeled vehicles. 
     Several designs have been proposed by the prior art to eliminate the problems associated with the turning of tandem wheeled vehicles. For example, U.S. Pat. No. 5,398,949 discloses a roller skate having a steering mechanism which allows the operator to execute figure skating maneuvers. The roller skate includes a steering cushion mechanism and a pivotal-turntable brake wheel mechanism. The steering cushion mechanism utilizes either a combination of screws and springs, or resilient members in conjunction with the axle of each wheel. In certain instances, a combination of resilient members, screws, and springs is utilized. However, the mechanism is still somewhat complicated because the frame must be designed to accommodate all of the additional parts. 
     U.S. Pat. No. 4,382,605 shows a steering mechanism for tandem wheeled vehicles. The mechanism includes a frame to which a pair of suspension members is attached. Two subsuspension members are also attached to the frame, one at each point of attachment of the suspension members. Each subsuspension member carries two wheels. The subsuspension members allow their respective sets of wheels to turn and follow a curved path dictated by the operator. However, the steering mechanism requires the addition of a suspension member and a subsuspension member, both of which must be attached to the base. These additional members increase the number of parts and create a more complex system. 
     U.S. Pat. No. 1,778,850 shows a roller skate suitable for figure skating. The roller skate includes a main wheel which is centrally positioned below the skate and a pair of auxiliary wheels, such as casters, at the front and rear positions of the skate. The auxiliary wheels are typically of smaller diameter than the main wheel and capable of swivelling. However, the auxiliary wheels are free to swivel uncontrolled, thereby creating an imprecise control system. 
     While the foregoing arrangements address the need for providing simple and inexpensive turning capabilities to tandem wheeled vehicles, the problem persists. Most of the prior art focuses on arrangements suitable only for roller skates and figure skating. Others are unable to adequately provide a mechanism that is simple and easy to manufacture. Consequently, it remains difficult to turn tandem wheeled vehicles. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to overcome the disadvantages of the prior art. 
     It is another object of this invention to provide a steering mechanism for tandem wheeled vehicles. 
     It is yet another object of this invention to provide a steering mechanism for tandem wheeled vehicles which is simple in design. 
     It is yet another object of this invention to provide a steering mechanism for tandem wheeled vehicles that is inexpensive to manufacture. 
     In accordance with the objects of this invention, a turning mechanism is provided for vehicles equipped with tandem wheels. The turning mechanism includes a base with a bottom surface to which a caster is mounted. The caster includes an axle and a wheel which is mounted on the axle. Since casters are well known in the field, a detailed description of casters and their components will not be provided. Only the parts essential to providing an understanding of the invention are described. A pair of rotation limiters having resilient properties is positioned with each rotation limiter on one side of the caster. Each rotation limiter is attached at one end to the respective end of the axle corresponding to its position on the side of the caster. The opposite end of each rotation limiter is attached to the bottom surface of the base. Each of the rotation limiters applies a tension force to one side of the caster. The tension force applied by each individual rotation limiter is equal and the tension tends to force the caster to swivel in the direction of that particular rotation limiter. Since this tension force is equal for each of the rotation limiters, the net result is that the two tension forces cancel each other and the caster remains in a straight orientation. 
     In order to execute a turn, the base is tilted in the desired turning direction. This action forces the caster to swivel in the same direction. The force applied by the tilted base also increases the tension on one of the rotation limiters; the one opposite of the turning direction. This increased tension acts on the caster to reduce the degree of swivelling which would freely occur. 
     The rotation limiters provide a certain level of stability to the overall operation of the steering mechanism. First, the rotation limiters maintain the caster in a straight orientation. Next, the rotation limiters prevent the caster from swivelling excessively during turns. In order to accomplish this task, it is evident that there are a variety of materials with resilient properties that are capable of being substituted while performing the same function. For example, a band having elastomeric properties may function as a rotation limiter. As yet another example, a spring could also function as a rotation limiter. 
     In one embodiment of the invention, the turning mechanism is provided with a mounting plate attached to the bottom surface of the base. The mounting plate provides a reinforced surface for attaching the caster. This may be necessary in situations where the material from which the base is constructed is incapable of withstanding the forces that will act upon it during regular operation. 
     In an application of the invention, a skateboard is equipped with the turning mechanism. The skateboard includes a base which has a bottom surface, a front portion, and a rear portion. A first caster is rotated so that it is facing forwardly and positioned at the front portion of the base. The first caster is then secured to the bottom surface of the base. The first caster includes a first axle and a first wheel which is mounted on the first axle. 
     A first pair of rotation limiters is positioned with each rotation limiter on one side of the first caster. Each of the first pair rotation limiters is attached at one end to the corresponding end of the first axle. The opposite end of each of the first pair of rotation limiters is attached to the bottom surface of the base. The rotation limiters are preferably selected such that they have resilient properties. Each of the first pair of rotation limiters applies a tension force to the first caster which urges it to rotate in the direction of the rotation limiter. The tension forces applied by each of the first rotation limiters react with each other and cancel. The net result is that the first caster remains in a straight orientation when the base is in a horizontal position. 
     A second caster is rotated so that it is facing rearwardly and positioned at the rear portion of the base. The second caster is then secured to the bottom surface of the base. The second caster includes a second axle and a second wheel mounted on the second axle. A second pair of rotation limiters is positioned with each rotation limiter on one side of the second caster. Each rotation limiter of the second pair of rotation limiters is attached at one end to the corresponding end of the second axle. The opposite end of each of the second pair of rotation limiter is attached to the bottom surface of the base. Each of the second pair of rotation limiters applies a tension force to the second caster which urges it to rotate in the direction of that particular rotation limiter. The two tension forces react with each other and cancel so that the second caster remains in a straight orientation. 
     In order to turn, the base is tilted in the desired turning direction. The first caster responds by swivelling in the same direction. The second caster, on the other hand, swivels in the opposite direction. The force applied by the base also places an increased tension in two of the rotation limiters, one rotation limiter from the first pair and one rotation limiter from the second pair. These increased tensions act to respectively reduce the degree of swivelling which would normally occur in the first and second casters. 
     The above and many other objects, features and advantages of this invention will be better understood from the ensuing description of selected preferred embodiments, which should be read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a bottom plan view of the turning mechanism. 
     FIG. 1 b  is a side elevational view of the turning mechanism. 
     FIG. 2 a  is a bottom plan view of the turning mechanism during a turn. 
     FIG. 2 b  is a front view of the turning mechanism during a turn. 
     FIG. 3 a  is a bottom plan view of another embodiment of the turning mechanism during a turn. 
     FIG. 3 b  is a front elevational view of the same embodiment during a turn. 
     FIG. 4 a  is a bottom plan view of a skateboard which utilizes the turning mechanism. 
     FIG. 4 b  is a side elevational view of a skateboard which utilizes the turning mechanism. 
     FIG. 5 a  is a bottom plan view of an embodiment of the skateboard which utilizes a spring as a rotation limiter. 
     FIG. 5 b  is a side elevational view of the same embodiment. 
     FIG. 6 b  is a bottom plan view of a skateboard during a turn. 
     FIG. 6 b  is a front elevational view of a skateboard during a turn. 
     FIG. 7 b  is a bottom plan view of another embodiment of the skateboard during a turn. 
     FIG. 7 b  is a front elevational view of the same embodiment during a turn. 
     FIG. 8 a  is a bottom plan view of another embodiment of the skateboard, which utilizes a caster mount and a mounting plate to secure the casters. 
     FIG. 8 b  is a side elevational view of another embodiment of the skateboard, which utilizes a caster mount and a mounting plate to secure the casters. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawing, and initially to FIGS. 1 a  and  1   b , a turning mechanism  10  is shown mounted to a base  12  which includes a bottom surface  14 . The base  12  can take on a variety of shapes and may be composed of various materials depending on the specific application. A mounting plate  16  is attached to the bottom surface  14  of the base  12 . A caster  18  is secured to the mounting plate  16 . The mounting plate  16  provides a reinforced surface for securing the caster  18 . The mounting plate  16  may be made of any appropriate material capable of providing the necessary wear resistance. For example, a metal or composite material could be used if capable of providing the necessary features. 
     The caster  18  includes an axle  20  to which a wheel  22  is mounted. The caster  18  is capable of rotating about a swivel axis z. A rotation limiter  30  is positioned on each side of the caster  18 . In a preferred embodiment, the rotation limiter may be an elastomeric band. Each rotation limiter  30  is attached at one end to the bottom surface  14  of the base  12 . The opposite end of each rotation limiter  30  is attached to the corresponding end of the axle  20 . As seen in FIG. 1B, the swivel axis z is offset from the point of ground contact of the wheel  22 . Each rotation limiter  30  exerts a tension force on the caster  18  which urges it to rotate in the direction of the rotation limiter  30 . The rotation limiters  30  perform two basic functions for the steering assembly  10 . First, the rotation limiters  30  maintain the caster  18  in a straight orientation when the base  12  is positioned horizontally. Second, the rotation limiter  30  prevent the caster  18  from swivelling freely during turns. 
     Turning now to FIGS. 2 a  and  2   b , the turning mechanism  10  is illustrated while engaged in a turning maneuver. With particular reference to FIG. 2 b , the base  12  of the turning mechanism  10  is shown tilted in the direction of turn. As a result, the caster  18  is forced to swivel in the direction of the turn. A resulting tension t is maintained on the rotation limiter  30  which is in the direction of the turn. The tension t reacts with the caster  18  to minimize the degree of swivelling which takes place during the turn. 
     FIGS. 3 a  and  3   b  illustrates another embodiment of the turning mechanism  10 . As seen more particularly from FIG. 3 b , a turning maneuver is in progress. A base  12  is shown which includes a bottom surface  14 . A mounting plate  16  is attached to the bottom surface  14  of the base  12 . A caster  18  is secured to the mounting plate  16 . The mounting plate  16  provides a reinforced surface for attaching the caster  18 . The caster  18  includes an axle  20  to which a wheel  22  is mounted. The caster  18  is capable of rotating about a swivel axis z. This particular embodiment of the turning mechanism  10  incorporates a pair of rotation limiters  32  which take the form of a spring. The rotation limiters  32  are positioned one on either side of the caster  18 . Each rotation limiter  32  is attached at one end to the bottom surface  14  of the base  12 . The opposite end of each of the rotation limiter  32  is attached to the corresponding end of the axle  20 . Each rotation limiter  32  exerts a tension force on the caster  18  which urges it to rotate in the direction of the rotation limiter  32 . The rotation limiters  32  function to maintain the caster  18  in a straight orientation when the base  12  is horizontal, and to prevent the caster  18  from swivelling excessively during turns. 
     FIGS. 4A and 4B illustrate a skateboard  50  adapted to incorporate a turning mechanism  51  as previously described. The skateboard  50  includes a base  52  which has a front portion  54 , a rear portion  55 , and a bottom surface  56 . A first mounting plate  58  is positioned at the front portion  54  of the base  52 . The first mounting plate  58  is then attached to the bottom surface  56  of the base  52 . A second mounting plate  59  is positioned at the rear portion  55  of the base  52 . The second mounting plate  59  is then attached to the bottom surface  56  of the base  52 . 
     A first caster  60  is rotated so that it is facing forwardly and secured to the first mounting plate  58 . The first caster  60  includes a first axle  62 . A first wheel  64  is mounted on the first axle  62 . The first caster  60  is also capable of rotating about a swivel axis z. A second caster  72  is rotated so that it is facing rearwardly and secured to the second mounting plate  59 . The second caster  72  includes a second axle  74 . A second wheel  76  is mounted on the second axle  74 . The second caster  72  is capable of rotating about a swivel axis z. 
     A first pair of rotation limiters  80  is positioned with each rotation limiter  80  on one side of the first caster  60 . In a preferred embodiment, the rotation limiter may be an elastomeric band. Each of the first pair of rotation limiters  80  is attached at one end to the corresponding end of the first axle  62 . The opposite end of each of the first pair of rotation limiters  80  is attached to the bottom surface  56  of the base  52 . Each of the first pair of rotation limiters  80  applies a tension force to the first caster  60  which urges it to rotate in the direction of the rotation limiter  80 . The net result of these tension forces causes the first caster  60  to remain in a straight orientation when the base  12  is positioned horizontally. 
     A second pair of rotation limiters  82  is positioned with each rotation limiter  82  on one side of the second caster  72 . Each of the second pair of rotation limiters  82  is attached at one end to the corresponding end of the second axle  74 . The opposite end of each of the second pair of rotation limiters  82  is attached to the bottom surface  56  of the base  52 . Each of the second pair of rotation limiters  82  applies a tension force to the second caster  72 . The net result of these tension forces maintains the second caster in a straight orientation. As illustrated in FIGS. 4 a  and  4   b , the first and second pair of rotation limiters  80 ,  82  take the form of elastomeric bands. 
     Turning now to FIGS. 5 a  and  5   b , an alternative embodiment of a skateboard  50  is illustrated. The skateboard  50  includes a base  52  which has front portion  54 , a rear portion  55 , and a bottom surface  56 . A first mounting plate  58  is positioned at the front portion  54  of the base  52 . The first mounting plate  58  is next attached to the bottom surface  56  of the base  52 . A second mounting plate  59  is positioned at the rear portion  55  of the base  52 . The second mounting plate  59  is then attached to the bottom surface  56  of the base  52 . 
     A first caster  60  is rotated so that it is facing forwardly and secured to the first mounting plate  58 . The first caster includes a first axle  62  to which a first wheel  64  is mounted. The first caster  60  is capable of rotating about a swivel axis z. A second caster  72  is rotated so that it is facing rearwardly and secured to the second mounting plate  59 . The second caster  72  includes a second axle  74  to which a second wheel  76  is mounted. The second caster  72  is capable of rotating about a swivel axis z. 
     A first pair of rotation limiters  84  is positioned with each rotation limiter  84  on one side of the first caster  60 . Each of the first pair of rotation limiters  84  is attached at one end to the corresponding end of the first axle  62 . The opposite end of each of the first pair of rotation limiters  84  is attached to the bottom surface  56  of the base  52 . A second pair of rotation limiters  86  is positioned with each rotation limiter  86  on one side of the second caster  72 . Each of the second pair of rotation limiters  86  is attached at one end to the corresponding end of the second axle  74 . The opposite end of each of the second pair of rotation limiters  86  is attached to the bottom surface  56  of the base  52 . As illustrated in FIGS. 5A and 5B, this embodiment incorporates a first and second pair of rotation limiters  86  which take the form of springs. 
     FIGS. 6 a  and  6   b  illustrate a skateboard  50  engaged in a turning maneuver. With particular reference to FIG. 6 a , the base  52  of the skateboard  50  is shown tilted in the direction of turn. As a result, the first caster  60  is forced to rotate in the direction of the turn. The second caster  72 , on the other hand, rotates in the opposite direction. The force applied to the base  52  in order to tilt it in the turning direction also places an increased tension t in one rotation limiter from the first pair of rotation limiters  80  and one rotation limiter from the second pair of rotation limiters  82 . These increased tensions act respectively on the on the first and second casters  60  and  72  to reduce the degree of swivelling which would normally occur. 
     FIGS. 7 a  and  7   b  illustrate an embodiment of the skateboard  50  which employs springs as rotation limiters. The skateboard is illustrated while engaged in a turning maneuver. With particular reference to FIG. 7 b , the base  52  of the skateboard  50  is shown tilted in the direction of turn. As a result, the first caster  60  is forced to swivel in the direction of the turn. The second caster  72 , on the other hand, rotates in the opposite direction. The force applied to the base  52  in order to tilt it in the turning direction also places an increased tension in one rotation limiter from the first pair of rotation limiters  84  and one rotation limiter from the second pair of rotation limiters  86 . These increased tensions t act on the first and second casters  60  and  72 , respectively, to reduce the degree of swivelling which would normally occur. 
     FIGS. 8 a  and  8   b  illustrate yet another embodiment of a skateboard  150  equipped to adapt a turning mechanism  151 . The skateboard  150  includes a base  152  which has front portion  154 , a rear portion  155 , and a bottom surface  156 . A first mounting block  157  is positioned at the front portion  154  of the base  152  and secured to the bottom surface  156  of the base  152 . A second mounting block  167  is positioned at the rear portion  155  of the base  152  and secured to the bottom surface  156  of the base  152 . The first and second mounting blocks,  157  and  167 , have a right triangular profile and are positioned so that their hypotenuses generally face each other. A first mounting plate  158  is angled to correspond to the angular displacement between the base  152  and the hypotenuse of the first mounting block  157 . The first mounting plate  158  is then secured to both the first mounting block  157  and the bottom surface  156  of the base  152 . A second mounting plate  159  is angled to correspond to the angular displacement between the base  152  and the hypotenuse of the second mounting block  167 . The second mounting plate  159  is then secured to both the second mounting block  167  and the bottom surface  156  of the base  152 . 
     A first caster  160  is rotated so that it is facing forwardly and secured to the first mounting plate  158 . The first caster includes a first axle  162  to which a first wheel  164  is mounted. The first caster  160  is capable of rotating about a swivel axis z. A second caster  172  is rotated so that it is facing rearwardly and secured to the second mounting plate  159 . The second caster  172  includes a second axle  174  to which a second wheel  176  is mounted. The second caster  172  is also capable of rotating about a swivel axis z. The first and second mounting blocks,  157  and  167  offset the swivel axis z such that it is not perpendicular to the ground surface. By offsetting the swivel axis z, there is a natural tendency for the first and second casters  160 ,  172  to maintain a straight orientation. Furthermore, when the first and second casters  160 ,  172  are rotated a specific angular displacement, the turning radius that would normally be traced with a swivel axis perpendicular to the ground is reduced due to the offset of the swivel axis z. Thus, the base  152  must also be tilted to a greater degree than necessary in a skateboard without the mounting blocks  157 ,  167  in order for the first and second casters  160  and  172  to trace the same turn. 
     A first pair of rotation limiters  184  is positioned with each rotation limiter  184  on one side of the first caster  160 . Each of the first pair of rotation limiters  184  is attached at one end to the corresponding end of the first axle  162 . The opposite end of each of the first pair of rotation limiters  184  is attached to the bottom surface  156  of the base  152 . A second pair of rotation limiters  186  is positioned with each rotation limiter  186  on one side of the second caster  172 . Each of the second pair of rotation limiters  186  is attached at one end to the corresponding end of the second axle  174 . The opposite end of each of the second pair of rotation limiter  186  is attached to the bottom surface  156  of the base  152 . Turning of this particular embodiment is accomplished in essentially the same manner previously described. 
     It will be appreciated that there are various modifications that may be made to the disclosed embodiments. For example, there are numerous materials that the rotation limiters can be made from. Also, the degree of offset applied to the swivel axis may be varied by selectively choosing the angles of the mounting blocks. Furthermore, the rotation limiters may be attached to various locations within the assembly. For example, one end of a rotation limiter may be attached to an axle while the opposite end is attached to the mounting block. 
     While the invention has been described with reference to selected preferred embodiments, it should not be limited to those embodiments. Rather, many modifications and variations will become apparent to those skilled in the art without departure from the scope and spirit of this invention as defined in the appended claims.