Abstract:
A lift includes a first telescoping member including a flange for attaching the lift to a vehicle, a second telescoping member coupled to the first telescoping member, and a tool coupled to the second telescoping member, wherein the tool is movable along two orthogonal axes of motion as determined by the two telescoping members. The telescoping members include at least two nested slides. A first slide includes a first pair of rollers on one side thereof and a second pair of rollers opposite the first pair. The second slide includes a pair of opposed U-shaped channels that enclose the rollers to provide a telescoping action. If one axis of motion is vertical, a block is included between each pair of rollers. Each block is dimensioned to engage the bottom of a channel, whereby the blocks help stabilize the motion of the first slide. Motion along two axes is controlled by actuation of a single switch.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a lift for loading or unloading goods into a light duty motor vehicle such as a van, utility vehicle, minivan, or even a large scooter such as a golf cart.  
         [0002]     A variety of small motorized scooters have been developed to carry a seated person through areas intended for pedestrian traffic. These scooters are battery powered, ride on either three or four small wheels, and are relatively compact but can be rather heavy because of the battery and electric motor. Unlike powered or unpowered wheelchairs, motorized scooters are usually not driven into a van or other vehicle with a person seated on the scooter. Rather, a lift is provided for attaching a scooter to the van for traveling long distances.  
         [0003]     Powered wheelchairs and scooters are evolving toward each other, making terminology imprecise. One manufacturer avoids the problem and calls its product a “highly maneuverable vehicle.” Some vehicles have wheels at the corners of a rectangle with the driven axle parallel to one side of the rectangle. Other vehicles have wheels at the corners of a diamond, with the driven axle parallel to a diagonal of the diamond. As used herein, “scooter” is intended to be generic to all such vehicles for aiding a person of limited mobility.  
         [0004]     Scooter lifts are either external, as illustrated in U.S. Pat. No.  5 , 011 , 361  (Peterson) and U.S. Pat. No.  5 , 567 , 107  (Bruno), or internal, as illustrated in U.S. Pat. No.  5 , 205 , 700  (Lin et al.) and U.S. Pat. No.  5 , 853 , 282  (Bechler et al.). External lifts typically have a fold-down platform for receiving the scooter. An internal lift is typically a small derrick mounted in the rear portion of a vehicle that hooks onto a portion of the scooter for lifting.  
         [0005]     An exterior platform lift is typically attached to the rear of a vehicle, e.g. via a trailer hitch, and is exposed to dirt and weather. Further, such a lift increases vehicle length and substantially changes the driving characteristics of the vehicle when carrying a scooter. An interior lift typically hooks onto a scooter in two or more places but does not prevent the scooter from turning, which can make it difficult to load the scooter.  
         [0006]     Enclosed or interior platform lifts are known the art, typically for raising an occupied wheelchair into a vehicle. Such lifts are attached to the side of a vehicle, and usually require a substantial re-working of the structure of the vehicle, e.g. replacing a portion of the frame and floor of a vehicle, as disclosed in U.S. Pat. No.  6 , 190 , 112  (Danilovic). Such lifts are quite expensive, often too expensive for those who need the lift. Enclosed platforms often take up a substantial amount of interior space, which can be a problem is smaller vehicles such as a minivan. Interior platform lifts are essentially restricted to vans and minivans. Station wagons, utility vehicles, pick-up trucks, and other light duty motor vehicles are unlikely candidates for such lifts because of lack of space or lack of weather protection.  
         [0007]     It is known in the art to provide a platform lift with a powered, telescoping mast or column; see the Peterson patent, U.S. Pat. No.  5 , 984 , 613  (Motilewa), or U.S. Pat. No.  6 , 007 , 290  (Schulz et al.). These lifts are for scooters. Platform lifts with more than one axis of movement (vertical or z-axis) are wheelchair lifts that are part of a highly modified vehicle and typically have a scissors type of action for moving the platform vertically and rotate the platform about one end to a vertical position; e.g. see U.S. Pat. No.  4 , 958 , 979  (Svensson) and U.S. Pat. No.  6 , 435 , 804  (Hutchins). In the Svensson patent, the platform is stored under the floor of the vehicle when not lifting or lowering.  
         [0008]     Known external platforms typically have a single side from which the platform can be entered or exited. This is needlessly inconvenient and potentially dangerous because the entrance to the platform is often on the driver&#39;s side or traffic side of the vehicle; e.g. see the Peterson patent. Another inconvenience in lifts of the prior art having more than one powered axis of movement is a control system that has a separate button for each axis. The user is challenged in some way but is assumed to have the manual dexterity of a child playing video games when operating the controls for a lift.  
         [0009]     In view of the foregoing, it is therefore an object of the invention to provide an internal lift for light duty motor vehicles.  
         [0010]     Another object of the invention is to provides adequate location for the goods, i.e. not letting the goods dangle on the end of a rope, during lift and storage in a vehicle.  
         [0011]     A further object of the invention is to provide an internal platform lift that can store goods during transit.  
         [0012]     Another object of the invention is to provide a lift having a platform that can be entered from more than one direction.  
         [0013]     A further object of the invention is to provide a platform lift that fully retracts into a light duty motor vehicle.  
         [0014]     Another object of the invention is to provide a lift that operates in two axes of motion with the push of a single button.  
         [0015]     A further object of the invention is to provide an internal lift for light duty motor vehicles that does not require significant structural changes of the vehicle for installation.  
       SUMMARY OF THE INVENTION  
       [0016]     The foregoing objects are achieved in this invention in which a lift includes a first telescoping member including a flange for attaching the lift to a vehicle, a second telescoping member coupled to the first telescoping member, and a tool coupled to the second telescoping member, wherein the tool is movable along two orthogonal axes of motion as determined by the two telescoping members. The telescoping members include at least two nested slides. A first slide includes a first pair of rollers on one side thereof and a second pair of rollers opposite the first pair. The second slide includes a pair of opposed U-shaped channels that enclose the rollers to provide a telescoping action. If one axis of motion is vertical, a block is included between each pair of rollers. Each block is dimensioned to engage the bottom of a channel, whereby the blocks help stabilize the motion of the first slide. Motion along two axes is controlled by actuation of a single switch. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0018]      FIG. 1  is a perspective view of a lift constructed in accordance with a preferred embodiment of the invention and located in the rear portion of a minivan;  
         [0019]      FIG. 2  is a perspective view of a lift constructed in accordance with a preferred embodiment of the invention, showing the lift head fully extended horizontally and the platform fully extended vertically;  
         [0020]      FIG. 3  is a perspective view of a lift constructed in accordance with a preferred embodiment of the invention, showing the lift head fully retracted horizontally and the platform fully retracted vertically in a minivan;  
         [0021]      FIG. 4  is a perspective view of the lift head constructed in accordance with an alternative embodiment of the invention, wherein the platform is replaced by a box for holding goods;  
         [0022]      FIG. 5  is a perspective view of the lift head constructed in accordance with an alternative embodiment of the invention, wherein the platform is replaced by a fork for holding goods on a pallet;  
         [0023]      FIG. 6  is a detail of a roller and track mechanism for moving the lift head horizontally;  
         [0024]      FIG. 7  is a detail of a roller and track mechanism for moving the lift head horizontally;  
         [0025]      FIG. 8  is a detail of a roller and track mechanism for moving the lift head horizontally;  
         [0026]      FIG. 9  is a perspective view of the telescoping mast fully retracted;  
         [0027]      FIG. 10  is a perspective view of the telescoping mast partially extended;  
         [0028]      FIG. 11  is a perspective view of the telescoping mast fully extended;  
         [0029]      FIG. 12  is a perspective view of the telescoping mast with cut-aways showing the roller and track mechanism for guiding the mast sections;  
         [0030]      FIG. 13  is a rear perspective view of the telescoping mast with a cut-away showing the powered capstan for raising the mast sections;  
         [0031]      FIG. 14  is a perspective view of the telescoping mast with cut-aways showing the roller and track mechanism in greater detail;  
         [0032]      FIG. 15  is a perspective view of the powered screw for moving the lift head horizontally;  
         [0033]      FIG. 16  is a perspective view of the trapped nut and release mechanism attached to the lift head;  
         [0034]      FIGS. 17-20  are block diagrams of a circuit for providing single button control of the lift; and  
         [0035]      FIG. 21  is a block diagram of a microprocessor based circuit for providing single button control of the lift. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]      FIG. 1  is a perspective view of a lift constructed in accordance with the invention and mounted in a light duty motor vehicle, represented by minivan  10 . Lift  11  includes two telescoping members, horizontally telescoping member  12  and vertically telescoping mast  13 . The lower portion of vertically telescoping mast  13  is attached to platform  14 . As illustrated in  FIG. 1 , platform  14  is adapted to receive a motorized scooter. As further described below, a variety of tools can be attached to the moving end of vertically telescoping mast  13  to adapt the lift to a wide variety of tasks.  
         [0037]      FIG. 2  illustrates lift  11  fully extended horizontally and vertically. Horizontally telescoping member  12  includes base  21 , middle slide  22 , and inner slide  23  including head  24  to which vertically telescoping mast  13  is attached, preferably by welding. Vertically telescoping mast  13  includes base unit  26 , first slide  27 , second slide  28 , and end post  29 . For both members, the slides are hollow and nest within one another, like little boxes, to provide a compact but sturdy support. As described in detail below, each box has pairs of wheels on opposite sides thereof, near one end, to support the box and provide the telescoping action.  
         [0038]     In accordance with another aspect of the invention, platform  14  can be entered from either end. Platform  14  includes first wall  31  and second wall  32  on opposite sides of floor  33 . The ends are open, enabling entry from either end. This provides a great convenience for the user and eliminates the risk associated with entering the platform from the traffic (left) side of the platform. Floor  33  includes raised, transverse portions  36  and  37  for locating a scooter centrally on the platform. With the wheels locked, a scooter is relatively securely located for transit. A plurality of apertures in walls  31  and  32  provide attaching points for tie downs to further secure a scooter.  
         [0039]     The telescoping action can be powered by pneumatic, hydraulic, or other means. In a preferred embodiment of the invention, horizontal telescoping member  12  is powered by a threaded shaft powered by electric motor through suitable reduction gearing. Vertical telescoping member  13  is powered by woven tape  43  wound on a capstan (not shown in  FIG. 2 ) powered by electric motor  44  through suitable reduction gearing.  
         [0040]      FIG. 3  is a perspective view of lift  11 , showing platform  14  fully raised and head  24  fully retracted in minivan  10 . Depending upon application, one could rotate platform  14  about the rear edge to obtain even more compact storage. As it is, lift  11  and whatever cargo or goods may be on platform  14  are fully contained within minivan  10 , providing secure, protected storage during transport.  
         [0041]      FIG. 4  is a perspective view of an alternative embodiment of the invention, wherein platform  14  is replaced by box  47  for holding goods. Box  47  is suitably attached to the end post of vertically telescoping mast  13  by welding or other means. Box  47  can be provided with suitable skids or feet (not shown) for engaging the floor of the minivan to prevent rocking during transport.  
         [0042]      FIG. 5  is a perspective view of an alternative embodiment of the invention, wherein platform  14  is replaced by fork  49  for holding goods on a pallet. From these alternative embodiments, one can see that a great variety of tools can be attached to the vertically telescoping member in accordance with the invention. It is not intended to name them all individually but all are intended to be covered by the claims that follow.  
         [0043]      FIGS. 6, 7 , and  8  illustrate details of a roller and track mechanism for moving the lift head horizontally.  FIG. 6  illustrates the mechanism fully retracted. Head  24  is attached to inner slide  23 , which is supported on each side by at least a pair of rollers, such as rollers  51  and  52  within U-shaped channel  54 . Channel  54 , in turn, is attached to middle slide  22 , which is supported on each side by at least a pair of rollers, including roller  56  within U-shaped channel  58 . Channel  58  is attached to the floor or, preferably, the frame of the vehicle by angle bracket  59 . Angle bracket  59  is preferably welded to channel  58  and includes a plurality of holes for bolting the lift to the floor of a vehicle or through the floor to the frame or other structural member, such as a crossbeam, of a vehicle. Stop block  61  provides a mechanical stop for a tool attached to the lift and prevents damage to the horizontal telescoping member when the tool is fully retracted.  
         [0044]      FIG. 7  illustrates the horizontal telescoping member partially extended. Rollers  56  and  57  are at the end of their travel in channel  58  but rollers  51  and  52  are not at the end of their travel in channel  54 . In  FIG. 8 , the horizontal telescoping member is fully extended. Rollers  56  and  57  are at the end of their travel in channel  58  and roller  51  (not shown in  FIG. 8 ) and roller  52  are at the end of their travel in channel  54 . At this point, mast  13  extends past the bumper of the vehicle to provide ample clearance for vertical movement of the telescoping mast.  
         [0045]     Because the rollers are attached at the rear of the slides, the front roller of each pair engages the lower side of a U-shaped channel and the rear roller of each pair engages the upper side of each U-shaped channel. Preferably, the rollers are pre-loaded, e.g. roller  51  is mounted slightly lower than roller  52 , to hold the slides approximately horizontal.  
         [0046]      FIGS. 9, 10 , and  11  illustrate the movement of telescoping mast  13 . Base unit  26  is attached to head  24 , preferably by welding. A single, cast unit could be used instead. In  FIG. 9 , telescoping mast  13  is fully retracted or raised. In this position, the mast clears the floor of the vehicle for retraction into the vehicle, despite the considerable length of the mast when extended.  
         [0047]      FIG. 10  illustrates mast  13  partially extended. Depending upon the internal construction of the mast, all sections may not extend together, as shown in  FIG. 10 . Tape  43  is attached at one end to end post  29 . First slide  27  and second slide  28  rest on their stops (not shown in  FIG. 10 ) and thus move with end post  29  until the slides encounter their respective stops at the upper end thereof. In this way, end post  29  does not extend until after second slide  28  extends, which is not until after first slide  27  is fully extended. Thus, the weakest part of the mast is not extended until last. By “weakest” is meant the ability to resist torque about a vertical centerline of mast  13 . Beca use the slides are wider, they resist torque better.  
         [0048]     In a preferred embodiment of the invention, gravity is used to lower the sections of the mast under the control of tape  43 , motor  44 , reduction gear  61 , and a capstan or drum (not shown) coupled to reduction gear  61 . That is, motor  44  provides a force that opposes gravity to a greater or lesser degree for retracting or extending mast  13 .  
         [0049]     Reduction gear  44  provides a secondary function in that the mast cannot drive motor  44  through the reduction gear. Thus, when motor  44  stops, the mast is effectively locked by the reduction gear. In theory, the mast could be retracted by an external force but such external force is unlikely and would have to be substantial, particularly if a load were held in a tool on the end of mast  13 .  
         [0050]     A tape drive has a further advantage in that, if the vehicle is parked on uneven ground, end post  29  simply stops when it encounters an obstacle because it is not being driven downward. Suitable control circuitry, not part of this invention, senses current through motor  44  and shuts off the motor if too much or too little current is drawn; the latter being the case when end post  29  encounters an obstacle.  
         [0051]      FIG. 11  illustrates mast  13  fully extended. If there is sufficient room, end post  29  is fully extended until an internal stop (not shown in  FIG. 11 ) is encountered. Slides  27  and  28  are also fully extended. In this position, in one embodiment of the invention, the lower end of end post  29  extends more than three feet below the level of the surface to which channel  58  ( FIG. 6 ) is attached.  
         [0052]     The long reach and sturdiness of telescoping mast  13  is due in part to the materials from which it is made (preferably steel) and in part to the internal design, which also provides a chatter free, smooth operation that is tight (small dimensional tolerances) without excessive friction.  FIG. 12  illustrates the channel and roller construction in cut-away. The construction of the sections of mast  13  are essentially symmetrical about a vertical centerline. Thus, only the left side of the mast is shown in cut-away and described in further detail.  
         [0053]     Base unit  26  includes opposed U-shaped channels  63  and  65  on either side of the base unit. The channels are opposed in the sense that the open parts of the channels face each other. Within channel  63  are roller  71 , roller  72 , and block  73 , all attached to first slide  27 . Block  73  is preferably made from Teflon®, Delrin® or other suitable, low friction material. Rollers  71  and  72  have a width that is slightly less than the width of block  73 . Block  73  and the corresponding block in channel  65  are spaced to engage the bottom (of the U) of each channel. Rollers  71  and  72  engage one side of channel  63  and block  73  engages the other side of the channel to pre-load the rollers. Thus, the rollers can turn freely within channel  63 . A third roller could be used to pre-load rollers  71  and  72  but block  73  is less expensive and just as effective. The combination provides a tight but chatterless movement. Another advantage of this design is its resistance to dirt and contamination. The unit can provide many years of trouble free, maintenance free service unless used in an extremely dirty or hostile environment.  
         [0054]     In theory, the friction of the rollers and blocks is a blessing when extending the mast and a burden when retracting the mast. In fact, the friction is so small compared with the weight of the components that friction is insignificant.  
         [0055]     The remainder of mast  13  is similarly constructed. First slide  27  includes opposed U-shaped channels  74  and  75  attached to opposite edges of the slide. Within channel  74  are roller  77 , roller  78 , and block  79 , all attached to second slide  28 . Second slide  28  includes opposed U-shaped channels  83  and  84  attached to opposite edges of the slide. Within channel  83  are roller  85 , roller  86 , and block  87 , all attached to end post  29 . End post  29  is attached to an end of woven tape  43 , which is wound over sheave  89 . The drive mechanism for tape  43  is illustrated in  FIG. 13 .  
         [0056]     In  FIG. 13 , woven tape  43  is wound around capstan  91  on shaft  93 , the number of turns depending upon whether mast  13  is retracted or extended. The free end of tape  43  passes over sheave  89  and extends down through openings in base unit  26 , first slide  27 , second slide  28 , and is attached to end post  29 . Capstan  91  is coupled to electric motor  44  by at least one gear reduction mechanism. In a preferred embodiment of the invention, motor  44  is coupled to shaft  95  by reduction gear  62  ( FIG. 11 ), which is preferably a worm driven gear to provide the locking effect described above. Shaft  95  is coupled to shaft  93  to by chain drive  97 , which also provide some gear reduction and an efficient coupling of power.  
         [0057]      FIG. 14  illustrates the channel and roller construction in greater detail. Channel  74  contains roller  77 , roller  78 , and block  79 , as described above. In order to prevent second slide  28  from dropping out of first slide  28 , channel  74  also includes stop block  101  held in place at the lower end of the channel by bolt  102 . Similarly, stop block  103  is located at the end of channel  75  and is held in place by bolt  104 . Stop blocks  101  and  103  have a secondary function of preventing dirt and debris from entering the channels. The ends are not sealed as such but the parts fit closely enough to keep the internal components clean.  
         [0058]      FIG. 15  illustrates the drive mechanism for horizontally telescoping member  12  ( FIG. 2 ). Channel  58  is attached to the floor of the vehicle by angle bracket  59 , as described above. Opposing channel  111  is also attached to the floor of the vehicle. At the ends of the channels, cross-member  112  is attached, holding the channels in fixed spatial relationship when the lift is not attached to a vehicle. Also attached to cross-member  112  is electric motor  115  coupled to threaded shaft  116  by reduction gear  117  and a chain drive (not shown) behind cross-member  112 . Reduction gear  117  is preferably a worm gear, which has the secondary benefit of locking threaded shaft  116 . The chain drive provides further reduction, high coupling efficiency, and isolates the output shaft in reduction gear  117  from loads imposed on threaded shaft  116 . The whole drive mechanism is also relatively flat, with electric motor  115  being the thickest element. Thus, a minimum amount of room is taken up by the drive mechanism.  
         [0059]     Magnet  118  is also mounted on cross-member  112  and actuates limit switch  131  ( FIG. 16 ) when inner slide  23  ( FIG. 6 ) is fully retracted. Limit switch  131  is one of a plurality of sense switches used in the lift but which, in themselves, are not part of the invention.  
         [0060]     Threaded shaft is coupled to head  24  ( FIG. 6 ) by a split nut and bearing assembly illustrated in  FIG. 16 . Threaded shaft  116  enters block  121 , which contains the split nut (not shown), which is held against shaft  116  by bolt  123 . Split nut assemblies are known in themselves in the art. In accordance with another aspect of the invention, bolt  123  is readily accessible and easily loosened to release the split nut, enabling head  24  to move freely should that ever become necessary.  
         [0061]     Limit switch  131  is mounted on panel  132  and senses when inner slide  23  ( FIG. 6 ) is fully retracted. Another limit switch, not shown, behind panel  132 , senses when the inner slide is fully extended. Flexible cable  128  contains a plurality of wires for controlling the operation of head  24 . One can control the lift with a hand held unit coupled to the lift by wire or by radio emission, as used for locks in an automobile. Cabling puts all the wires in a common sheath and improves the appearance of the lift.  
         [0062]     In accordance with another aspect of the invention, a single button controls the motion of the lift along two axes of movement. This can be accomplished with a few mechanical switches, relays, and some diodes for protection or under microprocessor control with semiconductor switches.  FIGS. 17, 18 ,  19 , and  20  are block diagrams of the same circuit for controlling motion along two orthogonal axes using mechanical switches and relays. Different aspects of the circuit are emphasized in the figures.  
         [0063]     In  FIG. 17 , rail  141  is coupled to the positive (+) terminal on a battery (not shown) and rail  142  is coupled to the negative (−) terminal on the battery. DC electric motor  143  drives horizontally telescoping member  12  and DC electric motor  144  drives telescoping mast  13 . In one embodiment of the invention, the rails are coupled to the DC motors through four relays,  148 ,  149 ,  150 , and  151  for reversing the polarity of the voltage applied to each DC motor, thereby individually reversing the direction of rotation of the output shaft of each motor.  
         [0064]     Either single pole, double throw ( SPDT), center-off, operator switch  153  or remote control  154  controls direction (extension and retraction). Block  154  represents the receiver portion of the remote control. The handheld transmitter is not shown. Movement along each axis is determined, in part by the positions of the    OUT limit switch  145 ,    IN limit switch  146 , up limit switch  147 ,    OUT relay  148 ,    IN relay  149 ,    UP relay  150 , and    DOWN relay  151 . The remote lockout feature is determined by    LOCKOUT limit switch  152 . Each limit switch and relay is a    SPDT switch, although one throw on switch  146  and  152  is not used.    
         [0065]      FIG. 17  illustrates the state of the lift when horizontal telescoping member  12  is fully retracted and telescoping mast  13  is fully raised; i.e. platform  14  ( FIG. 3 ) is raised and stowed in the vehicle. Thus, the  OUT  limit switch is not actuated, as indicated in  FIG. 17  by the absence of stippling.  
         [0066]     If switch  153  is thrown to the extend position or an extend button (not shown) on remote control  154  is actuated, then current flows from rail  141  through relay coil  148 ′, through switch  145 , and through either switch  153  or remote control  154  to rail  142 . Relay coil  148 ′ is magnetically coupled to the throw in switch  148 , pulling the throw to the right, coupling motor  143  to rail  141 . Current flows along the path indicated in heavier line from rail  141 , through switch  148 , through motor  143 , through switch  149  to rail  142 . Motor  143  turns, causing horizontally telescoping member  12  ( FIG. 1 ) to extend.  
         [0067]     When horizontally telescoping member  12  reaches a fully extended position,  OUT limit switch  145  is actuated, opening the circuit through relay coil  148 ′, causing the throw in switch  148  to revert to the left hand position, disconnecting motor  143  from rail  141  and connecting motor  144  to rail  142 . At this point, the horizontal telescoping member is fully extended and the telescoping mast is fully raised.    
         [0068]     Now current flows from rail  141  through relay coil  151 ′, through switch  145 , and through either switch  153  or remote control  154  to rail  142 . Relay coil  151 ′ pulls the throw in switch  151  to the right, connecting motor  144  to rail  141 . As descent begins, up limit switch changes poles, with no effect as it is presently out of the circuit.  
         [0069]     When vertical telescoping member  13  ( FIG. 1 ) reaches the intended down position (the ground), the operator releases switch  153  to its normal center position or releases the button on remote control  154 , deactivating relay coil  151 ′ and allowing switch  151  to revert to its normal left hand position, which disconnects motor  144  from rail  141 . The platform is now fully extended and lowered.  
         [0070]      FIG. 19  illustrates the state of the lift when the platform is fully extended and lowered. Thus, up limit switch  147  is not actuated, as indicated in  FIG. 19  by absence of stippling. Thus, switch  147  reverts to the position shown, coupling relay coil  150 ′ to switch  153  and control  154 .  
         [0071]     If switch  153  is thrown to the retract position or a retract button on remote control  154  is actuated, current flows from rail  141  through relay coil  150 ′, through switch  147 , and through either switch  153  or remote control  154  to rail  142 . Current through relay coil  150 ′ causes switch  150  to change poles, coupling motor  144  to rail  141 . Current flows through motor  144  in the circuit indicated in heavier line, which is in the opposite direction to the current shown in  FIG. 18 . Thus, motor  144  raises the platform, collapsing telescoping member  13  ( FIG. 1 ).  
         [0072]     As soon as vertical telescoping member  13  ( FIG. 1 ) reaches a fully raised position, as determined by up limit switch  147 , the switch is actuated, opening the circuit through relay coil  150 ′, causing switch  158  to revert to the left hand pole, and disconnecting motor  144  from rail  141 .  
         [0073]     At this point, the horizontal telescoping member is fully extended and the telescoping mast is fully raised. The circuitry is in the state shown in  FIG. 20 . When switch  147  changes poles, current flows from rail  141  through relay coil  149 ′, through switch  146 , through switch  147 , and through either switch  153  or remote control  154  to rail  142 . Current through relay coil  149 ′ causes switch  149  to change poles, coupling motor  143  to rail  141 . Current flows through motor  143  as indicated by the heavier line, which is opposite to the direction of the current flow illustrated in  FIG. 17 . Thus, motor  143  retracts the platform into the vehicle.  
         [0074]     When horizontal telescoping member  12  ( FIG. 1 ) reaches its innermost position as determined by  IN limit switch  146 , the switch is activated, disconnecting relay coil  149 ′, which deactivates switch  149  and disconnects motor  143  from rail  141 . Thus, by actuating a single switch, a user can extend or retract the telescoping mast and the horizontal telescoping member in the correct sequence.    
         [0075]     Changing ones mind in the middle of an operation simply reverses the process. For example, starting at the state shown in  FIG. 17 , after the telescoping horizontal member has, partially extended,  IN  limit switch has changed poles. Reversing operator switch  153  simply puts the control into the state shown in  FIG. 20  and the telescoping horizontal member retracts.  
         [0076]      FIG. 21  illustrates a control circuit implemented with semiconductor switches. This is not to say that there are no mechanical switches in a lift constructed in accordance with the invention. Mechanical switches remain useful as “fail-safe” devices. This aspect of the invention concerns single button operation, not other safety considerations. Computerized control facilitates making changes and adding features without having to modify hardware.  
         [0077]     In  FIG. 21 , microprocessor  161  is coupled to motor  143  by driver  162  and what is known as an H-bridge including switching transistors  164 ,  165 ,  166 , and  167 . A DC diagonal of the bridge is coupled to a batter, indicated by the plus sign (+) and the minus sign (−). Motor  143  is coupled to the AC diagonal of the bridge. The bridge acts a double pole, double throw switch by turning on the switching transistors in opposed arms to apply current in either direction through motor  143 . Specifically, when transistors  164  and  167  conduct, current flows from left to right through motor  143 . When transistors  165  and  166  conduct, current flows from right to left through motor  143 .  
         [0078]     Microprocessor  161  is also coupled to motor  144  by driver  172  and an H-bridge including transistors  174 ,  175 ,  176 , and  177 . Microprocessor  161  includes a plurality of inputs coupled to a plurality of sensors, represented by blocks  181 ,  182 ,  183 ,  184 ,  185  and  188 . Such sensors can be electrical, optical, or mechanical and include the control buttons operated by a user. Such sensors provide information on the location of inner slide  23  ( FIG. 6 ) and end post  29  ( FIG. 10 ), as the limit switches  145 - 148  do in the embodiment of  FIG. 17 . Microprocessor  161  is programmed to read the sensors and activate the drivers to extend or retract the lift by applying current to motors  143  and  144  in the proper sequence and direction.  
         [0079]     The invention thus provides an internal lift for a light duty motor vehicle that fully retracts into the vehicle. The lift provides adequate location for the goods, i.e. not letting the goods dangle on the end of a rope, during lift and storage in a vehicle, and can store goods during transit. When used as a scooter lift, the lift includes a platform that can be entered from more than one direction. Further, the lift operates in two axes of motion with the push of a single button. A lift constructed in accordance with the invention does not require significant structural changes of the vehicle for installation, that is, no changes beyond drilling bolt holes and some minor re-wiring.  
         [0080]     Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, in some applications, the telescoping mast could extend upward rather than downward, e.g. on vehicles having “barn doors” on the rear of the vehicle rather a lift gate or on vehicles having a large opening for a side door. Instead of moving vertically, the telescoping mast could move horizontally (sideways, orthogonal to the in and out movement of the head), e.g. for depositing a load beside the vehicle and over a curb from a position at the rear of the vehicle. A continuous drive, e.g. a chain or belt, can be used instead of a tape drive or a screw drive. The number of slides in a member is a design choice depending upon application. Either chain drive or both chain drives could be eliminated for direct or geared drive. One could replace a simple  DPDT  switch with a  DPDT  stepper switch (on-off-on-off) to provide what is literally a single button control for the embodiment of  FIGS. 17-21 .