Abstract:
An automated wheelchair for moving over a contact surface. The automated wheelchair includes an operator chair for seating the wheelchair operator, a control computer, an operator input device for transmitting operator inputs to the control computer, and two wheelchair wheels for propelling the wheelchair. Each wheelchair wheel includes extendable and retractable spokes. The extension and retraction of each spoke is controlled by a motor. At the ends of each spoke are contact sensor devices. The control computer is programmed to receive inputs transmitted from the contact sensor devices to generate a terrain profile. The control computer generates and sends control signals to each spoke motor in response to the operator inputs and in response to the terrain profile generated by the contact sensor devices. In a preferred embodiment the contact sensor devices are pressure sensor devices. Also in a preferred embodiment, rotatable pneumatic wheels are attached to both ends of each spoke. Preferably, a brake is applied to at least one pneumatic wheel per wheelchair wheel while the wheelchair is moving over the contact surface. Preferably, the automated wheelchair is capable of moving over a variety of contact surface types, including: a set of stairs with uniform rise to run ratio, a set of stairs with non-uniform rise to run ratio, a set of straight stairs, a set of curved stairs, over a curb or over rough terrain.

Description:
[0001]    The present invention relates to wheelchairs, and in particular, to automated wheelchairs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wheelchair usage has received recent attention in the media. It has been estimated that currently approximately 2 million Americans use wheelchairs. This number is expected to grow dramatically as the baby boomer generation grows elderly, as the population increases and as the age of life expectancy increases. Also, there has been recent media coverage on injured veterans from the war in Iraq and on mobility assistance devices such as wheelchairs and prosthetic limbs. However, despite recent improvements in technology and intense recent interest in wheelchairs, the modern wheelchair varies just slightly from traditional designs. Most importantly modern wheelchairs are incapable of performing tasks that non-wheelchair users take for granted continuously throughout the day. For example, prior art wheelchairs are incapable of going over a curb, up or down a set of stairs or traveling over rough terrain. Consequently, the wheelchair bound operator is continuously reminded of his predicament and is forced to adjust his daily existence to fit into a society that has been seemingly designed without consideration for wheelchair bound people. 
         [0003]    What is needed is a better automated wheelchair. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides an automated wheelchair for moving over a contact surface. The automated wheelchair includes an operator chair for seating the wheelchair operator, a control computer, an operator input device for transmitting operator inputs to the control computer, and two wheelchair wheels for propelling the wheelchair. Each wheelchair wheel includes extendable and retractable spokes. The extension and retraction of each spoke is controlled by a motor. At the ends of each spoke are contact sensor devices. The control computer is programmed to receive inputs transmitted from the contact sensor devices to generate a terrain profile. The control computer generates and sends control signals to each spoke motor in response to the operator inputs and in response to the terrain profile generated by the contact sensor devices. In a preferred embodiment the contact sensor devices are pressure sensor devices. Also in a preferred embodiment, rotatable pneumatic wheels are attached to both ends of each spoke. Preferably, a brake is applied to at least one pneumatic wheel per wheelchair wheel while the wheelchair is moving over the contact surface. Preferably, the automated wheelchair is capable of moving over a variety of contact surface types, including: a set of stairs with uniform rise to run ratio, a set of stairs with non-uniform rise to run ratio, a set of straight stairs, a set of curved stairs, over a curb or over rough terrain. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows a block diagram of a preferred control system for a preferred embodiment of the present invention 
           [0006]      FIGS. 2-16  show a preferred embodiment of the present invention climbing stairs. 
           [0007]      FIGS. 17A-17B  show a preferred wheelchair wheel with spokes. 
           [0008]      FIG. 18  shows a preferred wheel. 
           [0009]      FIG. 19  shows preferred gearing. 
           [0010]      FIGS. 20-22  show details of a preferred wheelchair wheel. 
           [0011]      FIG. 23  shows a perspective view of a preferred embodiment of the present invention. 
           [0012]      FIGS. 24-25  show an automated wheelchair adjusting its height and tilt of the operator chair. 
           [0013]      FIGS. 26-30  show an automated wheelchair moving forward over a curb. 
           [0014]      FIGS. 31-33  show an automated wheelchair moving over rough terrain. 
           [0015]      FIG. 34  shows a top view a preferred automated wheelchair. 
           [0016]      FIG. 35  shows an automated wheelchair turning right. 
           [0017]      FIG. 36  shows an automated wheelchair turning left. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]      FIG. 23  shows a perspective view and  FIG. 1  shows a block diagram of a preferred embodiment of the present invention. 
         [0019]    Main computer controller  2  receives operator inputs via operator input device  1 . Corresponding control signals are sent to wheels  80 A and  80 B. Wheels  80 A and  80 B each include 6 spokes  21 - 26  that are controlled via motors  41 - 46  (see also  FIG. 1 ). At each end of each spoke are pneumatic wheels. For example, pneumatic wheels  21 A and  21 B are attached to opposite ends of spoke  21 . Each pneumatic wheel includes a pressure sensor. When a pneumatic wheel makes contact with a surface, the pressure within the wheel increases and a signal is sent back to main computer controller  2 . Main computer controller  2  records this data. The data includes the angle of the spoke and the extension of the spoke when surface contact was made. Main computer controller  2  is programmed to compile this data received from pressure sensors and to utilize this data to calculate a terrain profile. Then, main computer controller  2  sends appropriate control signals to motors  41 - 46  to move the spokes  21 - 26  in an appropriate fashion so that the wheelchair moves in its intended manner (for example, upstairs, downstairs, over rough terrain, to the left, to the right, forward or backwards). As wheelchair  50  continues its movement, data is constantly being stored by main computer controller  2  and a more accurate terrain profile is constantly being created. 
         [0020]      FIGS. 2-16  show a side view of wheelchair  50  so that only wheel  80 A is visible. It should be understood that wheel  80 B is on the opposite side (left side) of wheelchair  50 . For the sequence of events outlined in  FIGS. 2-16  for climbing stairs, as components on wheel  80 A are moved, corresponding components on wheel  80 B will be moved in a similar fashion. For example, if spoke  21  on wheel  80 A is moved 3 inches towards the floor, similarly spoke  21  on wheel  80 B will also be moved approximately 3 inches towards the floor. Likewise if a brake is applied to pneumatic wheel  23 A for wheelchair wheel  80 A, similarly a brake is applied to pneumatic wheel  23 A for wheelchair wheel  80 B. Also, safety spoke  88  has its twin on the opposite side and both move in coordination. 
       Safety Spokes 
       [0021]    In a preferred embodiment, safety spokes  88  do not lift or propel chair  50 . Rather, they are provided for extra stability in case the operator should shift his weight in a large motion or attempt to exit the chair. Or, also in case of an external person applying excessive loads which may tip the chair. 
       Wheelchair Wheels 
       [0022]      FIGS. 17A and 17B  show a preferred wheelchair wheel  80 . Wheelchair wheel  80 A includes wheel-half  80 A 1  and wheel-half  80 A 2 . Preferably, wheelchair wheel-halves  80 A 1  and  80 A 2  are appropriately aligned and then bolted together ( FIG. 17B ,  FIG. 22  and  FIG. 17A ). 
         [0023]      FIG. 18  shows details of wheel-half  80 A 1 . Motors  41 ,  42  and  43  are mounted onto wheel-half  80 A 1 .  FIG. 18  shows a cut-out view of the gearing underneath motor  41  to better explain the operation of wheel  80 . 
         [0024]    As described below in reference to  FIGS. 1-16 , motor  41  controls the motion of spoke  21 . Motor  41  turns gear  174  in response to commands from main computer controller  2 . Gear  174  meshes with gear  175  (see also  FIG. 19 ). Worm gear  177  is connected to gear  175  via common axis  176 . Worm gear  177  meshes with teeth on spoke  21 . 
         [0025]    To control the motion of spoke  21 , motor  41  turns gear  174 . The turning of gear  174  causes gear  175  to also turn. The turning of gear  175  causes axis  176  to turn which also causes worm gear  177  to turn. The turning of worm gear  177  causes spoke  21  to extend. The direction of extension depends upon the direction of turning of worm gear  177 . 
         [0026]    At the end of spokes  21 - 26  are rotatably attached pneumatic wheels  21 A- 26 B ( FIG. 17 ). Each pneumatic wheel is free to rotate unless a brake has been applied to the wheel to prevent its rotation. In one preferred embodiment, at least two pneumatic wheels with brakes applied are in contact with a surface at any given moment. For example, in  FIG. 2 , brakes  72 A,  75 A, and  73 A ( FIG. 1 ) have been applied to pneumatic wheels  22 A,  25 A and  23 A respectively. By applying a brake to the pneumatic wheels, wheelchair  50  achieves traction on the floor and is able to move backwards as wheels  80 A and  80 B rotate counterclockwise and forwards as wheels  80 A and  80 B rotate clockwise. 
       Climbing Stairs 
       [0027]    An operation of a preferred embodiment of the present invention climbing stairs is described by reference to  FIGS. 2-16 . 
         [0028]    In  FIG. 2 , the user has turned “on” wheelchair  50  via operator input device  1  (see also  FIG. 1 ). Absolute spoke encoders  12  transmit the positions of spokes  21 - 26  to main computer control  2 . Absolute spoke encoders  99  transmit the positions of safety spokes  98  to main computer control  2 . Chair level sensor  131  transmits the current chair level of the wheelchair. Main computer control  2  also accesses its memory  14  to check the last known position of wheelchair  50  components and the known terrain surrounding wheelchair  50 . 
         [0029]    In  FIG. 3 , the user has moved a joystick located on operator input device  1  backwards. This has caused a signal to be sent from operator input device  1  to main computer control  2 . Main computer control  2  has then sent a corresponding signal to motor controllers  5 A- 5 C ( FIG. 1 ) to control the movement of wheelchair wheels  80 A and  80 B. 
       Proportional Integral Differential (PID) Servo Control System to Control Wheelchair Wheel Movement 
       [0030]    As shown in  FIG. 1 , each motor controller  5 A- 5 C sends control signals to two motors through a pair of H-Bridges. For example, motor controller  5 A sends control signals through H-Bridges  31  and  32  to motors  41  and  42 . Electricity from batteries  60  and  61  is routed through slip rings  63  to the H-Bridges. Then the H-Bridges proportion the 24V DC power from batteries  60  and  61  to the motors. Incremental motor encoders  51 - 56  then feed back the position of the motors  41 - 46  to motor controllers  5 A 1 - 5 A 3 . The above described components function as a Proportional Integral Differential (PID) Servo Control System to control motors  41 - 46 . 
         [0031]    In  FIG. 3 , after receiving the control signals from main computer controller  2 , motors  41 - 46  ( FIGS. 17A ,  17 B,  20 - 22 ) operate to move wheelchair  50  backwards. For example, motor  43  has extended spoke  23  ( FIG. 3 ) towards the floor, motor  45  has extended spoke  25  towards the floor and motor  42  has retracted spoke  22  into the wheel hub. Brakes  72 A and  75 A ( FIG. 1 ) are still applied to wheels  22 A and  25 A. However, brake  73 A has been released and wheel  23 A is free to rotate. Wheel  24 A at the end of spoke  24  has contacted the floor just prior to the first stair. A pressure sensor inside wheel  24 A has been tripped and a signal has been sent to main computer controller  2  so that main computer controller  2  can record the contact position of wheel  24 A in its memory. Likewise, each pneumatic wheel in contact with a surface is sending its contact information to main computer controller  2  so that main computer controller  2  can calculate a terrain profile. Each pneumatic wheel not in contact with the floor is also sending this non-contact information to the control computer. 
         [0032]    In  FIG. 4 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left. Spoke  23  has extended towards the floor, wheel  23 A is in contact with the floor and is free to rotate. Spoke  25  has extended further towards the floor, wheel  25 A is in contact with the floor and wheel brake  75 A is applied preventing its rotation relative to the spoke. Spoke  22  has retracted into the wheel hub, wheel  22 A is in contact with the floor and wheel brake  72 A is applied preventing its rotation. Spoke  24  has retracted into the wheel hub and wheel  24 A is in contact with the floor and is free to rotate. Pneumatic wheel  21 A of spoke  21  has made contact with the top of the first step of the stairs. This contact information has been transmitted from the pressure sensor switch in wheel  21 A to main computer controller  2 . Main computer controller  2  is programmed to assume that the top of the first step is horizontal and will begin to retract spoke  21  into the wheel hub as appropriate. Also, from the position shown in  FIG. 4 , wheelchair  50  will begin to move upward to climb the stairs. In a preferred embodiment, wheelchair  50  includes safety spoke  88 . As wheel chair  50  continues to move up the stairs, motor  98  will lower spoke  88  so that pneumatic wheel  88 A is always approximately 2 inches above the horizontal surface. 
         [0033]    In  FIG. 5 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and slightly upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Spoke  23  has extended further towards the floor, wheel  23 A is in contact with the floor and is free to rotate. Spoke  25  has extended further towards the floor, wheel  25 A is in contact with the floor and wheel brake  75 A is applied preventing its rotation. Spoke  22  has retracted into the wheel hub, wheel  22 A is in contact with the floor and wheel brake  72 A is applied preventing its rotation. Spoke  24  has retracted further into the wheel hub and wheel  24 A is in contact with the floor and is free to rotate. Spoke  21  has retracted into the wheel hub, wheel  21 A is in contact with the step and is free to rotate. The contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0034]    In  FIG. 6 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and slightly upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has further lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Spoke  26  has fully extended towards the stairs and wheel  26 B is extended and searching for the next contact point. Spoke  23  has retracted away from the floor at its full extension and wheel  23 A has lifted from the floor. Spoke  25  has extended towards the floor, wheel  25 A is in contact with the floor and wheel brake  75 A is applied preventing its rotation. Spoke  22  has retracted into the wheel hub, wheel  22 A is in contact with the floor and wheel brake  72 A is applied preventing its rotation. Spoke  24  has retracted into the wheel hub and wheel  24 A is in contact with the floor and is free to rotate. Spoke  21  has retracted further into the wheel hub and wheel  21 A is in contact with the step and is free to rotate. It should be noted that as wheel  21 A moves to the right it will eventually come to the edge of the step. When that happens, the pressure sensor inside pneumatic wheel  21 A will send a signal to main computer controller  2  indicating that the edge of the step has been located. Main computer controller  2  will then send a control signal to motor  41 A to move spoke  21  downward along the vertical edge of the step. In  FIG. 6 , the contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0035]    In  FIG. 7 , at a later time interval, wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and slightly upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has further lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Spoke  23  has extended to the left and wheel  23 B is extended and searching for the next contact point. Spoke  25  has retracted into the wheel hub and is centered about axis  103 . Wheel  25 A has lifted from the floor. Spoke  22  has extended towards the direction of the floor, lifting wheelchair  50 , wheel  22 A is in contact with the floor and wheel brake  72 A is applied preventing its rotation. Spoke  24  has extended towards the floor, lifting wheelchair  50 , and wheel  24 A is in contact with the floor and its brake is applied preventing its rotation relative to the spoke. Spoke  21  has retracted into the wheel hub and wheel  21 A is in contact with the step and is free to rotate. Wheel  26 B of spoke  26  has made contact with the steps and is free to rotate. In  FIG. 7 , the contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0036]    In  FIG. 8 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has further lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Due to the rotation of wheel  80 A, wheel  23 B of spoke  23  has made contact with the steps and is free to rotate. Spoke  25  is centered about axis  103 . Spoke  22  has extended towards the direction of the floor, wheel  22 A is in contact with the floor and is free to rotate. Spoke  24  has extended towards the floor and wheel  24 A is in contact with the floor and its brake is applied preventing its rotation. Wheel  21 A is in contact with the step and its brake is applied preventing its rotation. Spoke  26  has retracted into the wheel hub and wheel  26 B is in contact with the steps and is free to rotate. In  FIG. 8 , the contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0037]    In  FIG. 9 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and slightly upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has further lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Spoke  23  has retracted into the wheel hub, wheel  23 B is in contact with the steps and is free to rotate. Spoke  25  is centered about axis  103 . Spoke  22  is fully extended and wheel  22 A is no longer in contact with the floor. Spoke  24  has extended towards the floor and wheel  24 A is in contact with the floor and its brake is applied preventing its rotation. Wheel  21 A is in contact with the step and its brake is applied preventing its rotation. Wheel  26 B is in contact with the steps and is free to rotate. In  FIG. 9 , the contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0038]    In  FIG. 10 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and slightly upward. Motor  193  has kept wheelchair  50  at the operator selected recline angle. Motor  98  has further lowered safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above the floor. Spoke  23  has retracted into the wheel hub, lost contact with the horizontal face of the step, and then has re-established contact with the riser. Wheel  23 B is in contact with the riser and is free to rotate. Spoke  25  has extended to the left and wheel  25 B is extended and searching for the next contact point. Spoke  22  is centered about axis  103 . Spoke  24  has extended towards the floor and wheel  24 A is in contact with the floor and its brake is applied preventing its rotation. Wheel  21 A is in contact with the step and its brake is applied preventing its rotation. Wheel  26 B is in contact with the steps and is free to rotate. In  FIG. 10 , the contact information from the pneumatic wheels has been transmitted from their pressure sensor switches to main computer controller  2 . Main computer controller  2  is using this information to continue to calculate and update a terrain profile. 
         [0039]    In  FIGS. 11-13 , wheelchair  50  continues to move up the stairs in a fashion similar to that described above in reference to  FIGS. 1-10 .  FIGS. 14-16  show wheelchair  50  transitioning to the top of the stairs and also illustrate how safety spoke  88  traverses a step as it approaches the vertical edge of the step. 
         [0040]    In  FIG. 14 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left and is at the top of the stairs. Main computer controller  2  has compiled a terrain profile based on sensor information transmitted from the pressure sensor switches in the pneumatic wheels. Therefore, main computer controller  2  knows that safety spoke  88  is approximately 2 inches away from vertical edge  161  of the last step. Motor  98  has maintained the position of safety spoke  88  so that pneumatic wheel  88 A is approximately 2 inches above top of horizontal edge  162  of the second to the last step. Wheelchair  50  has briefly stopped at the position shown in  FIG. 14 . 
         [0041]    In  FIG. 15 , motor  98  has retracted safety spoke  88  upward away from the horizontal edge  162  to a height that is approximately 2 inches higher than floor  163 . 
         [0042]    In  FIG. 16 , wheel  80 A has continued its counterclockwise rotation and wheelchair  50  has moved to the left along floor  163 . 
         [0043]      FIGS. 1-16  illustrate clearly how this design of a wheelchair can travel up a set of stairs. Traveling down a set of stairs is done in a similar fashion, except the procedure is followed in a reverse order. For example,  FIG. 16  shows wheelchair  50  at the top of the stairs.  FIG. 13  shows wheelchair  50  as it begins its descent.  FIG. 11  shows wheelchair  50  towards the bottom of the stairs.  FIG. 2  shows wheelchair  50  at the bottom of the stairs. Preferably, on descent the operator will indicate “stairs present” so that safety spokes  88  can probe for the first step. 
       Wheelchair Stand-Up, Tilt and Level 
       [0044]    In a preferred embodiment, wheelchair  50  is capable of rising in height and tilting forward to make it easier for the operator to sit into the wheelchair or to get up from the chair. For example, in  FIG. 24  spokes  21 ,  24 ,  22  and  25  are extended towards the floor so that wheelchair  50  has risen in height. Also, main computer controller  2  has sent signals to motor  193  ( FIG. 1 ) to tilt wheelchair  50  forward. By being higher and tilted forward, it is easier for the operator to exit from wheelchair  50 . Preferably the positioning of wheelchair  50  is initiated by a command from the operator. 
         [0045]    In  FIG. 25 , the operator has sent control signals so that spokes  21 ,  24 ,  22  and  25  have retracted into the wheel hub. This has lowered wheelchair  50 . The operator has also tilted wheelchair  50  backwards by sending control signals to motor  193 . By having a lower center of mass and by having a seating position that is tilted backwards, the operator is transported more safely. 
       Traveling Forward Over a Curb 
       [0046]    As shown above, wheelchair  50  is capable of traveling backwards up a set of stairs. It is also possible to travel forward over a step, a set of small steps or a curb. 
         [0047]      FIGS. 26-30  illustrate a preferred wheelchair  50  traveling forward over a curb. It should be noted that regular stairs are traversed as described in detail above. 
         [0048]    In  FIG. 26 , wheelchair  50  is approaching a curb. 
         [0049]    In  FIG. 27 , wheelchair  50  has almost contacted the curb. At this point, the user inputs instructions via operator input device  1  to raise the wheelchair and to move forward over a curb. 
         [0050]    In  FIG. 28 , spokes  25 ,  22 ,  24 , and  21  have expanded towards the floor causing wheelchair  50  to rise in height. Brakes continue to be applied to wheels  22 A and  24 A. 
         [0051]    In  FIG. 29 , wheelchair  50  has moved to the right. Brakes are applied to wheels  23 A and  25 A. 
         [0052]    In  FIG. 30 , wheelchair  50  has moved to the right and has successfully climbed the curb. Brakes are applied to wheels  21 A and  24 A. 
       Traveling Over Rough Terrain 
       [0053]    Wheelchair  50  is also capable of traveling over rough or uneven terrain, as shown in  FIGS. 31-33 . 
         [0054]    In  FIG. 31 , wheelchair  50  is moving forward. Brakes are applied to wheels  21 A and  24 A. 
         [0055]    In  FIG. 32 , wheelchair  50  is traveling over a ditch (or a pothole under one wheel). 
         [0056]    Brakes are applied to wheels  23 A,  25 A and  22 A. 
         [0057]    In  FIG. 33 , wheelchair  50  has cleared the ditch and is continuing traveling over the rough terrain. Brakes are applied to wheels  26 B and  21 B. 
       Turning Left and Right 
       [0058]    In a preferred embodiment, wheelchair  50  can be turned either left or right at the discretion of the operator ( FIGS. 34-36 ). This turning can be done at anytime of operation enabling the operator to keep the chair centered in a stairway or negotiate a winding staircase. A set of mirrors will aid the operator while climbing stairs in reverse. 
         [0059]      FIGS. 34-36  show a top view of wheelchair  50 . In  FIG. 35 , the operator has moved the joystick on operator input device  1  ( FIG. 1 ) to the right sending a signal to main computer controller  2 . Main computer controller  2  controls motors  41 - 46  for wheels  80 A and  80 B so that wheel  80 B turns faster than wheel  80 A. This causes wheelchair  50  to turn to the operator&#39;s right. 
         [0060]    In  FIG. 36 , the operator has moved the joystick on operator input device  1  ( FIG. 1 ) to the left sending a signal to main computer controller  2 . Main computer controller  2  controls motors  41 - 46  for wheels  80 A and  80 B so that wheel  80 A turns faster than wheel  80 B. This causes wheelchair  50  to turn to the operator&#39;s left. 
         [0061]    Although the above-preferred embodiments have been described with specificity, persons skilled in this art will recognize that many changes to the specific embodiments disclosed above could be made without departing from the spirit of the invention. For example, although it was described above how two pneumatic wheels in contact with a floor surface or step surface had brakes applied for traction, it would also be possible to apply a brake to just one pneumatic wheel for traction or apply a brake to three pneumatic wheels for traction. Also, although the above preferred embodiment showed that operator input device included a joystick, the operator input device could be easily modified as appropriate. For example, it could include buttons for data entry or it could include voice recognition software. Voice recognition software would be preferable for operators who had no use of their hands or limited use of their hands. Also, although  FIGS. 2-16  show a set of stairs with a typical uniform rise to run ratio, it should be understood that the above described preferred embodiments could also easily traverse a set of stairs with a non-uniform rise to run ratio. Also, the preferred embodiment can be utilized for traversing a set of curved stairs. Therefore, the attached claims and their legal equivalents should determine the scope of the invention.