Abstract:
A vehicle access system for moving a passenger between the vehicle and ground. Some embodiments have an electrical system, a motive source coupled to the electrical system, an arm coupled to the motive source, a platform coupled to the arm, and a safety restraint system coupled to the electrical system and the platform. The vehicle access system has at least a vehicle access position and a ground access position, wherein the passenger can safely access the platform at either access position. The platform is unable to move from either access position until the safety restraint system is in place. Once operation of the access system has begun, it can continue to operate and move the passenger to one of the access positions even if the safety restraint system is subsequently removed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. provisional Application Ser. Nos. 60/361,989 filed 5 Mar. 2002 and 60/355,175 filed 7 Feb. 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present application relates generally to the field of vehicular access systems for handicapped persons, and more particularly to the field of safety devices related to those systems.  
         [0004]     2. Description of the Related Art  
         [0005]     People who have difficulty walking and people who use wheelchairs often have difficulty moving between different levels, such as getting into and out of vehicles. Consequently, there is a great need for devices that are capable of transporting people into and out of vehicles. Therefore, many different vehicular wheelchair access systems, such as lifts and ramps, have been developed to fulfill this need. These systems can be mounted on vehicles and manipulated between deployed and stowed positions with respect to the vehicle. When these systems are in the deployed position, wheelchair users typically must move their wheelchair along the lift and ramp platforms in order to transfer from the ground to the vehicle and from the vehicle to the ground. During the use of convention vehicle access systems, the passenger or operator can encounter potential dangers, such as falling off of the lift or ramp. Therefore, it is desirable to provide a safety system to assist lift operators and users in operating the access system in a safe manner. The invention of the present application is directed to satisfying these needs, among others.  
         [0006]     Many vehicle access systems such as passenger lifts and ramps are known in the art. However, there is a constant desire in the art to make these systems more reliable, cost effective and safe. Many safety features are currently used on several access systems, such as safety belts, barrier plates, and sensors. These restraining devices help prevent wheelchairs from rolling off the access system while in operation or can prevent operation of the access system altogether. However, they can have certain problems that can make them unsafe.  
         [0007]     Some vehicle access systems utilize belt buckle with an electronic safety interlock to prevent all movement of the access system until the safety belt is fastened to the buckle. In such devices, the safety interlock is a normally open electric switch located in the buckle. Thus, when the safety belt is unbuckled, the switch is open and the lift is incapable of operation. Once the safety belt is buckled, the switch is closed and the system is capable of operating. However, if the belt is unbuckled in the middle of operation, the system will stop operating. This can create a dangerous situation wherein the passenger is stuck in an elevated position in which the passenger cannot safely access either the vehicle or the ground. Furthermore, the passenger is stuck in this position, unrestrained by the safety belt. Thus, despite other safety features, the passenger may be able to roll off the access system while the system is in a position in which its is not safe to dismount. In such devices, operation of the system will not and cannot continue until the safety belt is buckled once again.  
         [0008]     In light of the problems and limitations described above, a need exists for a vehicle access system that is reliable, cost effective, and safe so that either safety restraint systems cannot be removed while in operation or that operation does not automatically cease between access positions even if the safety belt is removed during operation of the system. Each embodiment of the present invention achieves one or more of these results.  
       SUMMARY OF THE INVENTION  
       [0009]     The vehicle access system according to some embodiments of the present invention has an electrical system, a motive source coupled to the electrical system, an arm coupled to the motive source, a platform coupled to the arm, and a safety restraint system coupled to the electrical system and the platform. The vehicle access system can be mounted to the vehicle and operable to move a passenger between the ground and the vehicle. If the vehicle access system is mounted to the vehicle, it can have three or more main positions and numerous intermediate positions. The main positions can include a stowed position, vehicle access position (loading/unloading position into and out of the vehicle), and a ground access position (loading/unloading position onto and off of the ground). Thus, the passenger can safely access the platform at either access position. Once the passenger is situated and restrained on the platform, the platform can be moved between levels and the passenger can safely dismount the platform at the other access position. The platform, however, is unable to move from either access position until the safety restraint system is in place.  
         [0010]     Some embodiments of the present invention utilize a belt and buckle that has a current path through it as part of a safety restraint system. The current path is open when the belt and buckle are unbuckled and closed when they are buckled. The current path through the safety belt, in some embodiments, is coupled to a silicon controlled rectifier diode that is coupled to the electrical system of motive source. The diode has a turned-on and a turned-off state. The motive source can be powered when the diode is turned-on and cannot be powered when the diode has been turned-off. The diode is turned-on and off by a gate coupled to the current path in the buckle. When the current path through the buckle is closed, current flows to the gate of the diode to turn-on the diode and allow current to flow to the motive source. Once the diode is turned-on and so long as current continues to be drawn to the motive source, the diode can remain turned-on regardless of the state of the current path through the buckle. Thus, once operation of the access system has begun, it can continue to operate and move the passenger to one of the safe access positions even if the buckle is subsequently released.  
         [0011]     Other embodiments of the present invention can utilize one or more additional safety features alone or in combination with the above mentioned features. For example, some embodiments utilize roll-stops coupled to the platform, while other embodiments utilize a lock on the safety belt to prevent unbuckling during operation to prevent the passenger from rolling off the platform. Yet other embodiments utilize various audible and/or visual signals to alert the operator that the safety belt is unbuckled. Finally, other embodiments can utilize pressure switches coupled to the platform to prevent movement of the platform to the stowed position while the passenger is on the platform.  
         [0012]     A better understanding of the principles of the invention will become apparent from the following detailed description of the illustrated embodiments of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention is further described with reference to the accompanying drawings, which show preferred embodiments of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in embodiments which are still within the spirit and scope of the present invention.  
         [0014]     In the drawings, wherein like reference numeral indicate like parts:  
         [0015]      FIG. 1  is a perspective view of a vehicular wheelchair access and safety belt system with the platform unfolded and extending from the vehicle in a horizontal entry level position and the safety belt engaged;  
         [0016]      FIG. 2  is a perspective view of the system of  FIG. 1  with the platform at the ground level position and the safety belt engaged;  
         [0017]      FIG. 3  is a perspective view of the system of  FIG. 1  with the platform folded to a vertically stowed position and the safety belt engaged;  
         [0018]      FIG. 4  is an electrical schematic including for the wheelchair access system including the safety belt system of the present invention; and  
         [0019]      FIG. 5  is one embodiment of a wiring diagram for the electrical system of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any such alterations and further modifications in the illustrated embodiments, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0021]     Referring now to  FIG. 1  there is illustrated a vehicular access system  10 . Although access system  10  is illustrated as a wheelchair lift type system, it is also contemplated that principles discussed herein have application in wheelchair ramp type systems. Access system  10  is mounted in the door of a vehicle (not shown) to provide wheelchair passenger access to and from the vehicle. Access system  10  has a platform  22  movable in the inboard and outboard directions relative to the vehicle, as indicated by arrow I (inboard direction) and arrow  0  (outboard direction.) Examples of wheelchair access systems are provided in U.S. Pat. No. 6,238,169; U.S. Pat. No. 5,806,632; U.S. Pat. No. 5,261,779; U.S. Pat. No. 6,065,924; and U.S. Provisional Application Ser. No. 60/355,175 filed Feb. 7, 2002, each of which is incorporated herein by reference in its entirety. Another example of a wheelchair access system is The Braun Corporation&#39;s EV BRAUN ENTERVAN® wheelchair access ramp.  
         [0022]     In the illustrated embodiment, access system  10  includes a motive source  12  operatively coupled to paired parallelogram type lifting mechanisms  14 . Parallelogram lifting mechanisms  14  include vertical arms  20  to which an inboard end of platform  22  is pivotally coupled. When not in use, it is desirable to stow platform  22  in the vehicle in a vertical orientation adjacent the door of the vehicle to minimize its intrusion into the vehicle. Platform  22  can also be provided with foldable sections for stowage in a reduced height configuration, such as described in the aforementioned Provisional Application No. 60/355,175 filed Feb. 7, 2002.  
         [0023]     Access system  10  also includes articulated lever assemblies  16  pivotally connected to the inboard end of platform  22  at one end and to a corresponding one of the vertical arms  20  at their other end. Articulated lever assemblies  16  can include a longer arm pivotally connected to a shorter arm at a common center along with a saddle block for contacting the bottom arm of parallelogram lifting mechanisms  14 , such as shown and described in the aforementioned U.S. Pat. No. 6,238,169 and Provisional Application No. 60/355,175 filed Feb. 7, 2002. A safety shield  18  extends from a corresponding one of the vertical arms  20  along each side of articulated lever assemblies  16  to protect against the potential placement of a part of a person or object therebetween before and/or during lift operation.  
         [0024]     Motive source  12  is operable to swing lifting mechanisms  14  generally along path R to move platform  22  from the vertically stowed position of  FIG. 3 , to the transfer level position or horizontal entry level position of  FIG. 1 , to the ground level position of  FIG. 2 , and back. Motive source  12  can be electrically coupled to the vehicle power source and include hydraulic pumps and/or electrical motors and other components to accomplish the desired movement for lifting mechanisms  14 .  
         [0025]     Mounting members  93  are secured to a floor plate  56  of the vehicle. Lifting mechanisms  14  are pivotally mounted to a corresponding one of mounting members  93 . Each lifting mechanism  14  includes an upper arm  88  and a lower arm  90 . Upper arms  88  are each pivotally coupled at their inboard end to a corresponding one of the mounting members  93 . Lower arms  90  are also each pivotally coupled at their inboard end to a corresponding one of the mounting members  93  below upper arm  88 . Each lifting mechanism  14  also includes a cylinder  92  pivotally coupled at its outboard end to lower arm  90  and also to vertical arm  20 . The inboard end of each cylinder  92  is pivotally coupled to the inboard end of the respective upper arm  88  at mounting member  93 . A deploy assist mechanism  86  can be provided around each cylinder  92 . Further details regarding cylinder  92  and deploy assist mechanism  86  are provided in the aforementioned Provisional Application 60/355,175 filed Feb. 7, 2002.  
         [0026]     When platform  22  is in its vertically stowed position, there may be a tendency for platform  22  to drift in the outboard direction due to, for example, a slow loss of hydraulic pressure in cylinder  92 . When the platform drifts, it could push against the vehicle door, making opening of the door difficult and also damaging the interior of the vehicle. Thus, there is provided anti-drift mechanism  100 . One embodiment of anti-drift mechanism  100  is shown in the aforementioned Provisional Application No. 60/355,175 filed Feb. 7, 2002. Other embodiment anti-drift mechanisms are provided in U.S. patent application Ser. No. 09/702,397 filed on Oct. 31, 2000, which is incorporated herein by reference.  
         [0027]     Platform  22  is pivotally coupled at its inboard end to each of the vertical arms  20 . Platform  22  has side barriers  28  extending along each side thereof. Platform  22  can be provided with meshed grid-like or solid plate-like transfer surface between the side barriers and between the inboard/outboard ends of platform  22 .  
         [0028]     Access system  10  also includes a spring-loaded rollstop  46  pivotally connected to the outboard end of platform  22  that is normally spring-biased to a raised safety barrier position as shown in  FIG. 1 . Rollstop  46  includes feet  46   a ,  46   b  ( FIG. 1 ) that contact the ground to move rollstop  46  to lower rollstop  46  to transfer level position extending from the outboard end of platform  22  as shown in  FIG. 3 .  
         [0029]     Access system  10  includes a bridge plate  50  pivotally coupled to the inboard end of platform  22 . A pair of actuator assemblies can be provided to couple bridge plate  50  to each of the articulated lever assemblies  16 . The actuator assemblies and articulated lever assemblies  16  operate in concert such that contact between articulated lever assemblies  16  and bottom arms  90  of lifting mechanisms  14  variously raise and lower bridge plate  50  between a raised safety barrier position ( FIG. 2 ) and a generally horizontal transfer level position ( FIG. 1 .) Further details regarding bridge plate  50  are provided in the aforementioned Provisional Application 60/355,175 filed Feb. 7, 2002 and also in U.S. Pat. No. 6,238,169. Other mechanisms for raising and lowering bridge plate  50  are also contemplated.  
         [0030]     Access system  10  further includes handrails  42  extending horizontally from vertical arms  20  when platform  22  is deployed in a horizontal position as shown in  FIGS. 1 and 2 . When folded, as shown in  FIG. 3 , handrails  42  each extend along a corresponding one of the vertical arms  20 . A bumper  78  can be coupled to the upper side of each handrail  42  to eliminate or reduce noise and abrasion when the handrail is positioned against vertical arm  20 . Each handrail  42  further includes an outboard end bent to conform to the upper end of vertical arm  20  when folded thereagainst. A grip handle can be placed over the outboard ends of each handrail  42  to facilitate gripping thereof.  
         [0031]     A safety belt system  200  is provided with access system  10 . System  200  includes a safety belt  202  extending between handrails  42 . Safety belt  202  is mounted at one end to one of the handrails  42  and removably engaged to a buckle  204 , which is mounted on the other handrail  42 . It is contemplated that safety belt  202  can include a strap and end member like that of an automobile seat belt for engagement with buckle  204 . Other configurations are also contemplated, so long as safety belt  202  is removably engageable with buckle  204 . Safety belt  202  can be non-retractable, although a retractable belt is also contemplated. Buckle  204  can have any configuration suitable for engagement with the end member of safety belt  202 . Buckle  204  includes a current path therein that is coupled with the electrical system  210  of motive source  12  by, for example, electrical wiring  206 . It is contemplated the current path in buckle  204  is normally open, and is closeable upon engagement of the end member of safety belt  202  with buckle  204 . Closing the current path in buckle  204  enables electrical system  210  to provide power to move platform  22  with motive source  12 .  
         [0032]     Platform  22  has three main positions including the vertically stowed position ( FIG. 3 ), the horizontal transfer level position ( FIG. 1 ), and the ground level position ( FIG. 2 .) Access system  10  includes sensors providing signals to electrical system  210  indicating when the platform is at one of the three main positions. The platform position signals from platform sensors for the stowed position and the floor level position may be used to stop platform movement when the desired position is reached.  
         [0033]     When the current path in buckle  204  is closed by engaging the end member of belt  202  to buckle  204 , electrical system  210  can provide power to motive source  12  to move platform  22  between the three main positions with lifting mechanisms  14  based on operator signal input indicating the desired platform movement. When safety belt  202  is not coupled with buckle  204 , the current path of electrical system  210  in buckle  204  is open and platform movement cannot be initiated by operator input signals.  
         [0034]     The safety belt system of the present invention enhances operator control of the lift during platform movement. If the current path in buckle  204  is closed with the end member of safety belt  202 , and platform movement has been initiated by operator signal inputs, and the current path in buckle  204  is thereafter opened during platform movement by disengaging the end member of belt  202 , the current path in electrical system  210  is maintained for platform movement to one of the three main positions. However, platform movement can be stopped at any position intermediate the three main positions by the operator. Thus, the operator maintains control over lift operation even if safety belt  202  is unbuckled.  
         [0035]     When safety belt  202  is unbuckled, and when platform is at one of the three main positions or has been stopped by the operator at an intermediate position, the current path of electrical system  210  is open to prevent platform movement. Platform movement can continue when the end member of belt  202  is engaged to buckle  204  to close the current path in buckle  204 .  
         [0036]     In  FIG. 4 , there is shown an electrical schematic of one embodiment of electrical system  210  for providing power to move platform  22 . In  FIG. 5  there is shown one embodiment of a wiring diagram for electrical system  210  of  FIG. 4 . Electrical system  210  is electrically coupled to safety belt system  200 . In the illustrated embodiment, electrical system  210  includes an operator input device  212  electrically coupled to a microswitch station  214 . It is contemplated that input device  212  could also employ infrared or radio signals to communicate input signals from the operator. It is further contemplated that a programmable controller could be provided in lieu of or in addition to microswitches  214 . Electrical system  210  further includes a power source  218 . It is contemplated that power source  218  can be the vehicle&#39;s main battery or backup battery, or a stand-alone battery dedicated to electrical system  210 . Input device  212 , microswitches  214  and power source  218  are electrically coupled to a pump housing  215 .  
         [0037]     Pump housing  215  includes a drive means  220 , an up/fold controller  222 , a down controller  224  and an unfold controller  226 . In the illustrated embodiment, controller  222  is a controller which controls operation of drive means  220 , and controllers  224  and  226  are solenoids that control operation of valves of a hydraulic system coupled between drive means  220  and cylinder  92 . Drive means  220  includes a hydraulic pump and motor to supply hydraulic pressure to cylinders  92  to raise platform  22  from the ‘ground level position to the entry level position, and also to vertically fold platform  22  from the entry level position. An interlock  228  is provided to allow coupling of additional sensors and the like to electrical system  210 . For example, a sensor can be mounted on the vehicle door and coupled to electrical system  210  via interlock  228 . Control of the operation of platform  22  can be based on satisfaction of an external condition determined by the sensor, such as whether the vehicle door is completely open.  
         [0038]     Safety belt system  200  is electrically coupled between power source  218  and pump housing  215  to control the operation of drive means  220 . In the illustrated embodiment, safety belt system  200  includes a safety belt switch  230  in buckle  204 , a current flow control device  232  in the form of an SCR diode, and a resistor  234 . Current flow control device  232  includes gate G that prevents current flow therethrough when the current path in buckle  204  is open. When the current path in buckle  204  is open, current flow control device  232  disables electrical system  210  by blocking the current path to operate drive means  220  and controllers  222 ,  224 , and  226  with operator input signals from input device  212 .  
         [0039]     When the current path in buckle  204  is closed, current from power source  218  flows through resistor  234  and switch  230  to energize and open gate G of current flow control device  232 . With gate G open, current can flow through current flow restrictor  232 , and power is provided from power source  218  to operate controllers  222 ,  224  and  226  based on operator input signals from signal input device  212 . Such signals initiate folding or unfolding of platform  22  between the vertically stowed and horizontal entry level positions, and the moving platform  22  up or down between the horizontal entry level and ground level positions. If the current path in buckle  204  is opened by unbuckling belt  202  from buckle  204 , gate G remains opened until one of the platform positions is sensed at either stowed or floor level position or until platform operation is stopped by the operator. However, once one of the main positions of platform  22  is sensed or platform movement is stopped by the operator through signal input device  212 , power cannot be supplied to drive means  220  and controllers  222 ,  224 ,  226  until the circuit in buckle  204  is closed by engaging belt  202  to buckle  204 .  
         [0040]     In the illustrated embodiment, signal input device  212  includes an unfold input and a fold input selectable by the operator to provide signals indicative of the desired platform movement from the vertically stowed position to the horizontal transfer level position and back, respectively. Signal input device  212  also includes a down input and an up input selectable by the operator to provide signals indicative of the desired platform movement from the horizontal entry level position and the ground level position and back, respectively.  
         [0041]     It is contemplated that microswitch station  214  includes unfold/down microswitches and up/fold microswitches coupled to controllers  222 ,  224 ,  226  to control platform  22  movement in accordance with the commands received from signal input device  212  as selected by the operator. In the illustrated embodiment, the up/fold microswitch signals the up/fold controller  222  to start or stop drive means  220 . The unfold/down microswitch signals down controller  224  to open and close a first valve in the hydraulic system, and also signals unfold controller  226  to open and close a second valve in the hydraulic system.  
         [0042]     In operation, when the up input is selected by the operator and safety belt  202  is engaged to buckle  204 , controller  222  starts drive means  220  wherein the hydraulic pump provides pressurized hydraulic fluid to cylinder  92  to move platform  22  from the ground level position to the horizontal entry level position. Belt  202  can be disengaged from buckle  204  during this movement without affecting platform movement to the entry level position. When the platform reaches the entry level position sensors provide a signal to direct controller  222  to stop drive means  220 .  
         [0043]     When the fold input is selected by the operator and safety belt  202  is engaged to buckle  204 , controller  222  starts drive means  220  to provide pressurized hydraulic fluid to cylinder  92  to move platform  22  from the horizontal entry level position to the vertically stowed position. Belt  202  can be disengaged from buckle  204  during this movement without affecting platform movement to the vertically stowed position. When the platform reaches the vertically stowed position sensors provide a signal to direct controller  222  to stop operation of drive means  220 .  
         [0044]     When platform  22  is in the vertically folded position and safety belt  202  is engaged to buckle  204 , operator selection of the unfold input signals down controller  224  to open the first valve in the hydraulic system and also signals unfold controller  226  to open the second valve in the hydraulic system. Belt  202  can thereafter be disengaged from buckle  204  without affecting platform movement to the entry level position. Unfolding of platform  22  is controlled by directing the hydraulic fluid through the second valve, which includes or is in fluid communication with a restricted orifice. The restricted orifice causes the pressure to be relieved more slowly than would result if only the first valve were opened, thus&#39; slowing movement of platform  22  from the vertically stowed position to the horizontal entry level position. When the platform reaches the entry level position sensors provide a signal to direct controllers  224 ,  226  to shut the first valve and the second valve.  
         [0045]     When platform  22  is at the horizontal entry level position and safety belt  202  is engaged to buckle  204 , a down input from the operator signals down controller  224  to open the first valve to relieve hydraulic pressure from cylinder  92  to allow platform movement from the horizontal entry level position to the ground level position. Belt  202  can be disengaged from buckle  204  during this movement without affecting platform movement to the ground level position. There is no ground level sensor. See note on page 8.  
         [0046]     In one alternate embodiment, electrical system  210  does not include an unfold controller  226  coupled to a restricted orifice, but rather only a down controller  224  to open the first valve to relieve pressure from cylinder  92 . Hydraulic pressure is relieved through this first valve for platform movement both from the vertically stowed position to the entry level position, and from the entry level position to the ground level position. In such an alternate embodiment, the restricted orifice is not needed since controller  224  and the first valve coupled thereto allow platform  22  to unfold from the vertically stowed position at a rate within a desired range. Factors that influence whether the unfold rate of movement of platform  22  can be maintained in the desired range using only controller  224  and the first valve include the size of platform, the rates at which the desired range is established, and whether the first valve can be modulated for varying flow rates therethrough. Another factor is whether platform  22  is folded to a reduced height configuration when vertically stowed such as described in the aforementioned Provisional Application 60/355,175 filed Feb. 7, 2002. If platform  22  is provided as described therein, then only a single down controller  224  is needed since the reduced height, folded platform will unfold from the vertical position at a slower rate than if the platform were not folded to a reduced height configuration.  
         [0047]     Referring back to the illustrated embodiment, it is contemplated that the microswitches or other controller means can be configured so that with platform  22  in the entry level position signals from the unfold input and the up inputs of signal input device  212  are ignored or disabled. In the ground level position, signals from the fold input, unfold input and down input of signal input device  212  are ignored or disabled. In the vertically stowed position, signals from the fold input, down input and up input of signal input device  212  are ignored or disabled.  
         [0048]     From the horizontal entry level position, the operator can then either fold the platform to the vertically stowed position or again move the platform to the ground level position as discussed above. When platform  22  is at the horizontal entry level position, a wheelchair passenger can be positioned on platform  22  from the vehicle. Pressure switch  216  thereafter prevents movement of platform  22  from the horizontal entry level position to the vertically stowed position if the fold input is selected. Selection of the down input moves platform  22  from the horizontal entry level position to the ground level position where the wheelchair passenger exits the lift. Another wheelchair passenger may then board the lift, and platform  22  raised from the ground level position to the entry level position by selecting the up input. The wheelchair passenger on platform  22  can then enter the vehicle. Again, pressure switch  216  prevents platform  22  from being moved from the horizontal entry level position to the vertically stowed position until the wheelchair is off of platform  22 . When platform  22  is clear of passengers, the fold input can be selected to move platform  22  to the vertically stowed position. Further examples and discussion regarding pressure switch  216  are provided in U.S. patent application Ser. No. 09/430,436 which is incorporated herein by reference in its entirety.  
         [0049]     It is also contemplated that the fold and unfold inputs of signal input device can be integrated into a single input, and that the up and down inputs can be integrated into a single input. The single unfold/fold input would unfold the platform if the platform is determined to be in a folded condition, and fold the platform if the platform is determined to be at horizontal transfer level position. Activation of the single up/down input will lower the platform if the platform is determined to be in a horizontal entry level position, and raise the platform if the platform is determined to be at the ground level position. Platform movement can be stopped and reversed by providing a second input after initial movement has been initiated.  
         [0050]     It is contemplated that the fold and unfold inputs and up and down inputs on signal input device  212  can be momentary contact switches that require the operator to hold the switch closed for platform movement to a desired position. If the operator releases the switch, then platform movement stops immediately. When the switch is again activated, platform operation continues toward the desired position so long as the operator maintains the switch closed.  
         [0051]     It is also contemplated that the fold and unfold inputs and the up and down inputs on the input control device can be continuous contact switches that require the operator to activate the switch for platform movement. If the operator releases the switch, platform movement continues to the appropriate vertically stowed, horizontal entry level or ground level position unless the switch is reactivated or a stop signal is received.  
         [0052]     A further embodiment of safety belt system  200  contemplates providing an alarm to signal disengagement of safety belt  202  from buckle  204 . The alarm could be an audio signal and/or visual signal to the operator. The alarm would notify the operator that safety belt  202  is unbuckled so that the operator can take an appropriate action. For example, upon indication that safety belt  202  is unbuckled, the operator may want to immediately stop platform movement by providing the appropriate signal through signal input device  212 . For embodiments in which input device includes momentary contact switches, the operator could simply release the switch to stop platform movement intermediate one of the main positions. In another example, the operator may desire that platform movement continue to one of the main positions. For embodiments in which input device includes momentary contact switches, the operator could simply maintain the switch in the closed position to continue platform movement to the next main position.  
         [0053]     A further embodiment of safety belt system  200  includes a safety belt locling system that prevents unbuckling of safety belt  202  from buckle  204  during platform movement. Such an interlock device would receive a signal from electrical system  210  that platform movement has been initiated, and would thereupon lock safety belt  202  to buckle  204 . Once platform movement has stopped by reaching one of the main positions, or has been stopped by the operator, safety belt  202  would automatically unlock from buckle  204 , and could thereafter be unbuckled.  
         [0054]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.