Abstract:
An extendable ramp assembly includes a chassis, a first ramp slidably movable relative to the chassis and hingably connected to the chassis, and a second ramp carried by the first ramp and movable relative to the chassis and the first ramp. Separate structure is provided for extending and retracting both the first and second ramps. A first mechanism is provided for detecting whether either or both of the first and second ramps abuts an obstruction when at least one of the ramps is being extended. A second mechanism is provided for stopping the extension of at least one of the ramps or for retracting at least one of the ramps in the event of the detecting mechanism detecting the obstruction.

Description:
FIELD OF THE INVENTION 
     This invention relates to a ramp. More especially but not exclusively the ramps are for entrance to or egress from vehicles. The ramp of the invention can however be used in other application such as for entrance to or egress from buildings. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     According to the invention there is provided an extendible ramp comprising: 
     i) a chassis; 
     ii) a first ramp slidable movable relative to the chassis and hingable connected to the chassis; 
     iii) a second ramp carried by the first ramp and movable relative to the chassis and the first ramp; 
     iv) means for extending and retracting the first ramp; 
     v) means for extending and retracting the second ramp; 
     vi) means for detecting whether the ramp abuts an obstruction when the ramp is being extended; and 
     vii) means for retracting the ramp if it abuts an obstruction during extension. 
     The first ramp can be hingably connected to a linking member movable relative to the chassis. 
     A ramp can be movable by a rotatable leadscrew received in a feed nut. 
     The feedscrew can be driven by an electric motor. Means for monitoring the current drawn by the motor can be provided. Means for stopping or reversing the motor if the current drawn exceeds a predetermined value can be provided. 
     The second ramp can be slidably receivable within the first ramp. 
     Means for extending a ramp or a member can be resiliently biased away from a switch such that when load on the extending means or members exceeds a predetermined value the switch is actuated actuating means for stopping or retracting the ramp. 
     A top face of a ramp can be pivotally mounted. Means for urging the face to a pivotted position and means for biasing the face away from a pivoted position can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described by way of non-limiting example by reference to the accompanying figures of which: 
     FIG. 1 is a side elevation of a first embodiment in a retracted configuration; 
     FIG. 2 is a cutaway plan view of the embodiment of FIG. 1; 
     FIG. 3 is a side elevation of the embodiment of FIG. 1 with the first and second ramps deployed; 
     FIG. 4 is a side elevation of the embodiment of FIG. 1 with the face pivoted; 
     FIG. 5 is a top plan of the embodiment of FIG. 1 with first and second ramps deployed; 
     FIG. 6 is a side elevation of a second embodiment in a retracted configuration; 
     FIG. 7 is a side elevation of a second embodiment in an extended configuration; 
     FIG. 8 is an enlarged partially cutaway side view of the embodiment of FIG. 6 in an extended configuration; and 
     FIG. 9 is an enlarged partial side view of the embodiment of FIG. 8 in a retracted configuration. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrated embodiment is primarily intended for fitment to a low floor bus. 
     Cassette  1  is provided for a mounting of operative components of the ramp. The ramp can be supplied to vehicle builders for inclusion in the vehicle at an early stage of construction or retrofitted to an existing vehicle. 
     Cassette  1  is secured to the vehicle for example by screw threaded fasteners with edge  2  about flush with the vehicle side. 
     Motor  10  is provided. In the illustrated embodiment this motor is a low voltage dc motor. It will be apparent to the skilled however that other motors, such as air and hydraulic motors could be provided. 
     Drive shaft  11  of motor  10  is provided with a bevel gear  12 . Second drive shaft  13  is mounted for rotation in bearings  14 . Drive shaft  13  provided with a plurality of bevel gears,  15 ,  16 ,  17 . Second bevel gear  15  is in meshing engagement with bevel gear  12  such that actuation of motor  10  causes second drive sheet  13  to rotate. 
     First and second lead screws  20 ,  21  are provided about perpendicular to second drive shaft  13 . Lead screws  20 ,  21  are each provided with a bevel gear  22 ,  23 . Third bevel gear  16  of second drive shaft  13  is in meshing engagement with fifth bevel gear  22  of first lead screw  20 . 
     Fourth bevel gear  17  of second drive shaft is in meshing engagement with sixth bevel gear of second lead screw. 
     A first feed nut  30  is in meshing engagement with first lead screw  20  and second feed nut  31  is in meshing engagement with second lead screw  21 . Linking member  32  extends between first and second feed nuts  30 ,  31 . 
     Actuation of motor  10  thus causes linking member  32  to move in direction of arrow A. 
     Those skilled in the art will have little difficulty in devising other ways of providing a linearly movable linking member  32 . 
     In preferred embodiments of the invention the end of one or both feed screw is provided with a dog  33 . Engagement of dog  33  with a tool allows linking member to be moved in the event of failure of actuating motor  10 . This is useful in emergencies for example if motor  10  fails. The shape of dog  33  is not critical for the purposes of the invention. Slots engagable by bladed tools or male or female squares or hexagons can be used. In some cases it is desirable to use a standard square for example corresponding to the drive shaft of a torque or ratchet wrench. However when used in public service vehicles with a roster of drivers the tool may be subject to loss by petty theft. To reduce the likelihood of this a dog of special shape with a tool of corresponding shape can be provided. 
     Hinge  40  is provided on the edge of linking member  32  nearer the edge. In the illustrated this comprises a strip of flexible polyurethane. Those skilled in the art will have no difficulty in devising other hinges. 
     First ramp  50  is hingably mounted of linking member  32  by hinged member  40 . Actuation of motor  10  thus causes first ramp  50  to be extended or retracted. 
     A position sensor for sensing the position of ramp  50  is provided. In the illustrated embodiment the position sensor comprises microswitches  60 ,  61  adjacent the lead screws toward the ends of the lead screws. As the ramp is extended or retracted to the limit of normal operation linking member  32  or feed nuts actuate the microswitches. A control unit  65  can then switch off motor  10  and, as will be apparent hereafter control other features of the invention. 
     In some embodiments of the invention control unit  65  monitors the current drawn by motor  10 . If movement of the ramp is inhibited for example by contacting a person motor  10  draws a higher current. The control unit senses this and if the current exceeds a predetermined value control unit  65  either switches off or reverses motor  10 . 
     Those skilled in the art will have little difficulty in devising suitable control units. A preferred system uses the multiplexing scheme described in U.S. Pat. No. 4,907,222 the disclosure of which is incorporated herein by reference. By way of example control unit  65  may comprise lo an Intellitec PMC CPU 98A and two Intellitec PMC I/O Modules. 
     Edge  2  of the cassette  1  is provided with a resiliently biased flap  70 . The resilient bias urges the flap to close slot  71  through which the first ramp  50  can be projected by motor  10 . Flap  70  serves a number of purposes. Flap  70  improves the aesthetic appearance of the vehicle. Flap  70  reduces the amount of dirt and water entering the cassette. Flap  70  reduces the height of the step between the platform of the vehicle and the ramp. 
     The top surface of ramp  50  is generally provided with a ribbed surface or other textured surface which may be resilient to improve traction of people and vehicles such as wheelchairs ascending or descending the ramp  50 . Second ramp  80  is received in the first ramp  50  when the ramp as a whole is retracted. Second ramp  80  is slidably movable relative to the first ramp. In the illustrated embodiment this is achieved by providing slide guides  81  at the edges of the first in which are received the edges of second ramp. 
     In the illustrated embodiment second ramp  80  is actuated by a pneumatic ram  81 . It will be appreciated however that other ways of actuating the ramp can be used examples include hydraulic rams and electric motors. In response to a command from control unit  65 , ram  81  is actuated. In general the first ram will be partially extended at this point. It will be understood however that this is primarily a matter of convenience. 
     Desirably second ramp is retractable in the event that it contacts an obstruction. In the illustrated embodiment ram  81  is mounted resiliently on the first ramp. Resilient bias  85  urges ram  81  away from microswitch or other actuator  86 . The bias is sufficiently strong that actuation of the ram  81  does not cause ram  81  to actuate actuator  86  unless the ramp meets an obstruction. In a similar manner to that described hereinbefore control unit  65  can then cause ram  81  to stop or retract. 
     Face  90  of second ramp  85  is pivotally mounted on the ramp  85  toward the outer edge  91 . The underside of face  90  is provided with a first wedge  92 . Second wedge  93  is provided on the ramp. Faces  94 ,  95  of the first and second wedges abut. The first and second wedges are relatively movable. In the illustrated embodiment second wedge  93  is movable. Movement of the wedges in a first direction urges the face  90  upwardly. This provides a more even ramp than would otherwise be the case. In the illustrated embodiment second wedge is actuated by a second pneumatic ram  98  controlled by control unit  65 . Those skilled in the art will have little difficulty in devising other suitable ways of actuating the second wedge such as electric motors or hydraulic cylinders. Preferably, as is shown the illustrated embodiment, a resilient bias  99  is provided urging the second ram to a position in which the face is not raised. In this arrangement if supply of air to the ram fails face  90  will retract allowing the ramp to be stowed. It will be apparent that it is important for face  90  not to be pivoted until its free edge is sufficiently advanced for it not to fail. Similarly the face should be allowed to retract before second ramp is withdrawn. Those skilled in the art will have no difficulty in devising suitable ways in which control unit  65  can ensure that this is the case. 
     In some embodiments of the invention face  90  is not pivotally movable. 
     FIGS. 6 to  9  illustrate an embodiment of this kind. Face  90  is not pivotally mounted and consequently second pneumatic ram resilient bias and first and second wedges are not provided. 
     Flap  90  is provided with nose  100 . A cam track  101  is provided towards the end of the first ramp. Nose  100  of the flap engages cam track  101 . A second flap  110  is also provided. Second flap is resiliently mounted on the bottom of the first ramp. A resilient bias urges the second flap in the direction of arrow B to close the slot through which the second ramp extends. The free tip  102  engages nose  100 . In the closed configuration the arrangement is as shown in FIG. As the first ramp extends the resilient bias of the first and second flaps is overcome. The first ramp descends the cam track and abuts the top surface of the ramp providing a relatively obstruction free surface and second flap is urged outwardly. FIG. 8 shows the ramp extended. As the ramp is retracted the ends of the ramps move in board of the tip of the second flap. The resilient bias causes the flap to rotate in the direction of arrow B. The first ramp is moved upwardly as the nose engage the cam track. This allows the second flap to rotate fully home before the resilient bias urges the first flap into the position shown in FIG.  9 . 
     In some embodiments of the invention a hole is provided near the front edge of the second ramp. A tool can be provided having an arm receivable in the hole. This allows the second ramp to be deployed or stowed manually if desired. 
     In some embodiments sensors are provided to sense the condition of one or more of the handbrake, the speed of the vehicle and the vehicle doors. The control unit  65  can monitor the sensor or sensors and for example can prevent actuation of the ramp until the handbrake is on and the vehicle speed is less than a predetermined speed for example 5 kmh −1 . 
     In an embodiment of the invention the control unit prevents deployment of the ramp unless the vehicle is moving at less than 5 kmh −1 , the handbrake is on and the doors are closed. 
     To deploy the ramp a deployment switch is pressed and held until the ramp is fully deployed. Release of the deployment switch causes the control unit to retract the ramp. When the ramp is fully extended the deployment switch can be released and the doors opened. The control unit may actuate a ramp extended warning indicator. A warning signal for example visual and/or audible may be given during deployment. 
     To retract the ramp the control unit monitors the handbrake and the doors. Retraction can not be performed unless the doors are shut and the handbrake is on. Redeployment can be prevented until a time delay for example 10 seconds has expired. 
     A number of ways of reducing the likelihood of the vehicle being driven while the ramp is extended can be provided. They can include one or more of a warning signal for example visual and/or audible, the control unit could actuate the vehicle&#39;s brakes such as the handbrake could prevent engagement of the vehicle drive and/or could prevent an engine speed from being increased above a particular level. 
     In some embodiments of the invention the vehicle must be stationary before the ramp can be deployed. 
     Other ways of detecting an obstruction either alone or in combination with those previously described can be used. An example is providing a resettable fuse for example one employing positive temperature coefficient materials. When the motor draws too high a current for example following contact with an obstruction the fuse trips. This prevents the motor from working. The control unit monitors the fuse tripping and when power is restored retracts the ramp. A further example provides a member carried by the ramp on a resilient portion of the ramp such that if the ramp abuts an obstruction the member moves relative to other parts of the movable ramp. Abutment causes the member to actuate a switch stop or reversing the ramp. A still further example transposes the position of the switch and member.