Abstract:
A wheelchair includes a frame, a seat, a pair of wheels, and a locking mechanism. The seat is disposed on the frame. The pair of wheels is rotatably supported on the frame. At least one of the pair of wheels includes a removable section that is configured to form a part of an outer circumference of the wheel and to be removable when the wheel is at a predetermined angular position, and a remaining section that is configured to form the outer circumference of the wheel together with the removable section. The locking mechanism is configured to lock the wheel at the predetermined angular position. Under the condition where the wheel is locked, the removable section is separated from the remaining section to facilitate a person to get on and off the seat.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from Japanese Patent Application No. 2009-285520 filed Dec. 16, 2009 and Japanese Patent Application No. 2009-285521 filed Dec. 16, 2009. The entire contents of these priority applications are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a wheelchair for use by hospital patients, physically disabled people, elderly people in assisted living, and the like. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventionally, a wheelchair has been configured of a frame having left and right side sections, a seat section provided in the frame, and wheels disposed on each of the left and right side sections of the frame. Recently, some conventional wheelchairs have also been provided with a wheel separation mechanism for separating a special fan-shaped section of the wheel, which includes an outer circumferential part of the wheel, from the remaining section constituting the wheel while the wheel is in a specific separating position in order to provide the clearance necessary for a person to get on and off the seat section. 
         [0006]    Thus, when a person is getting on or off the seat section of the wheelchair, the special fan-shaped section of the wheel including the outer circumferential part of the wheel is separated from the remaining section while the wheel is in the special separating position in order to form the clearance necessary for getting on and off the seat section of the wheelchair. 
       SUMMARY OF THE INVENTION 
       [0007]    With the conventional structure described above, the wheel must be reliably placed in the separating position before separating the special fan-shaped section from the remaining section. However, it takes great care to visually determine when the wheel is in the correct separating position relative to the seat section. This shortcoming alone reduces the convenience of the wheel separation mechanism. 
         [0008]    In view of forgoing, it is an object of the present invention to provide a wheelchair in which the wheel is easily placed in the separating position. 
         [0009]    In order to attain the above and other objects, the present invention provides a wheelchair that includes a frame, a seat, a pair of wheels, and a first locking mechanism. The seat is disposed on the frame. The pair of wheels is rotatably supported on the frame. At least one of the pair of wheels includes a removable section that is configured to form a part of an outer circumference of the wheel and to be removable when the wheel is at a predetermined angular position, and a remaining section that is configured to form the outer circumference of the wheel together with the removable section. The first locking mechanism is configured to lock the at least one of the pair of wheels at the predetermined angular position. 
         [0010]    According to another aspect, the present invention provides a wheelchair that includes a frame, a seat, a pair of wheels, and a lifting mechanism. The seat is disposed on the frame. The pair of wheels is rotatably supported on the frame. At least one of the pair of wheels includes a removable section that is configured to form a part of an outer circumference of the wheel and to be removable when the wheel is at a predetermined angular position, and a remaining section that is configured to form the outer circumference of the wheel together with the removable section. The lifting mechanism is mounted on the frame and is configured to lift the at least one of the pair of wheels a predetermined distance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In the drawings: 
           [0012]      FIG. 1  is a right-side view showing the outer structure of a wheelchair in a running state according to an embodiment of the present invention; 
           [0013]      FIG. 2  is a right-side view showing the outer structure of the wheelchair in a state that a wheel is elevated off a contact surface; 
           [0014]      FIG. 3  is an enlarged view of the wheelchair around the wheel when the wheel is elevated off the contact surface; 
           [0015]      FIG. 4  is an enlarged cross-sectional view of an elevating mechanism and a positioning mechanism when the wheel is elevated off the contact surface; 
           [0016]      FIG. 5  is an enlarged left-side view of the elevating mechanism when the wheel is elevated off the contact surface; 
           [0017]      FIG. 6  is an enlarged cross-sectional view of the positioning mechanism when the wheel is in contact with the contact surface; 
           [0018]      FIG. 7  is an enlarged left-side view of the elevating mechanism when the wheel is in contact with the contact surface; 
           [0019]      FIG. 8  is an enlarged cross-sectional view showing a locking mechanism when a fan-shape plate is positioned at a locking position; 
           [0020]      FIG. 9  is a partial side view of the wheel when the wheel is positioned at a separating position and the fan-shape plate is positioned at a mounting position; 
           [0021]      FIG. 10  is an enlarged view of the locking mechanism when the fan-shape plate is positioned at the mounting position; 
           [0022]      FIG. 11  is an enlarged view of a safety mechanism when a removable section is mounted on a remaining section; 
           [0023]      FIG. 12  is an enlarged cross-sectional view of the locking mechanism when the removable section is mounted on the remaining section; 
           [0024]      FIG. 13  is a partial right-side view of the wheel when the removable section is separated from the remaining section; 
           [0025]      FIG. 14  is an enlarged view of the safety mechanism when the removable section is separated from the remaining section; and 
           [0026]      FIG. 15  is an enlarged cross-sectional view of the locking mechanism when the removable section is separated from the remaining section. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    A wheelchair according to embodiment of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
         [0028]    The terms “top”, “bottom”, “left”, “front”, “rear” and the like will be used throughout the description assuming that the wheelchair is disposed in an orientation in which it is intended to be used. 
         [0029]    The wheelchair according to the preferred embodiment includes a frame  1  having left and right side parts. A seat  2 , a backrest  3 , and footrests  4  are disposed on the frame  1  so as to be positioned in a center region between the left and right sides of the frame  1 . Large rear wheels  5  and small front wheels  6  are disposed one each on each of the left and right side parts of the frame  1 . 
         [0030]    The wheels  5  are freely rotatable about an axle S. The wheel includes a hub  5   c  fixed to the frame  1  (see  FIG. 8 ), and a fixing disc  5   d  fixed to the hub  5   c . The fixing disc  5   d  is formed with a locking hole  5   e  in which a locking pin  12   h  described later is inserted (see  FIG. 8 ). The left and right side parts of the frame are each provided with an armrest that can be retracted through a retracting mechanism, such as a flip-up mechanism. 
         [0031]    The wheelchair also includes a wheel separation mechanism  7  and a mounting mechanism  8 . The wheel separation mechanism  7  is configured by forming the right wheel  5  in two separate components, including a removable section  5   a  shaped like a folding fan and forming part of the outer circumference of the wheel  5  and a remaining section  5   b  comprising the entire wheel  5  excluding the removable section  5   a , and by providing the mounting mechanism  8  (see  FIG. 8 ) for detachably mounting the removable section  5   a  on the remaining section  5   b . The fan-shaped removable section  5   a  has an arc angle of about 120 degrees, while the remaining section  5   b  is formed in an arc shape having an arc angle of about 240 degrees for completing the circular shape of the wheel  5 . 
         [0032]    As shown in  FIG. 13 , the mounting mechanism  8  is provided on the adjoining surfaces of the removable section  5   a  and remaining section  5   b . Specifically, the mounting mechanism  8  includes engaging protrusions  8   a  disposed on the removable section  5   a , and engaging recessions  8   b  formed in the remaining section  5   b  at positions aligned with the engaging protrusions  8   a . The removable section  5   a  is detachably mounted on the remaining section  5   b  by engaging the engaging protrusions  8   a  in the engaging recessions  8   b . The remaining section  5   b  is pivotably mounted on the axle S and can be rotated to a separating position F for forming clearance K required for a person to get on and off the seat  2  when the removable section  5   a  is removed. 
         [0033]    The wheelchair also has an elevating mechanism  9  to lift the right wheel  5  off a contact surface M as shown in  FIG. 2 . As shown in  FIGS. 4 and 5 , the elevating mechanism  9  is configured of a base plate  9   a  mounted on the frame  1 ; a pair of left and right, upper links  9   b  pivotably mounted on the base plate  9   a  through a support pin  9   d  penetrating the base ends thereof; a pair of left and right L-shaped lower links  9   c  pivotably mounted on the base plate  9   a  through a support pin  9   e  penetrating the base ends thereof; afoot member  9   f  pivotably mounted on the distal ends of the lower links  9   c  via a pin  9   g ; an actuating link  9   h  having a middle part pivotably mounted on the distal ends of the upper links  9   b  via a pin  9   i , and a lower end pivotably mounted on middle parts of the lower links  9   c  via a pin  9   j ; an operating link  9   k  pivotably mounted on a lower front part of the frame  1  via a pin  9   l  (see  FIG. 1 ); a coupling rod  9   m  coupling one end (rear end) of the operating link  9   k  to an upper end of the actuating link  9   h ; and a handle  9   n  disposed on the other end (front end) of the operating link  9   k.    
         [0034]    When the outer periphery of the wheel  5  is resting on the contact surface M, as shown in  FIG. 7 , the operator can pull on the handle  9   n  to rotate the operating link  9   k  in one direction (counterclockwise in  FIG. 1 ), causing the actuating link  9   h  to rotate upward into a vertical state shown in  FIG. 5 . Through the upper links  9   b  and lower links  9   c  linked to the actuating link  9   h , the lower links  9   c  rotate downward into a vertical state as the actuating link  9   h  rotates upward. At this time, the foot member  9   f  disposed on the bottom of the lower links  9   c  contacts the contact surface M and lifts the wheel  5  off the contact surface M, as shown in  FIG. 5 . 
         [0035]    While the wheel  5  is elevated, the operator can push on the handle  9   n  to rotate the operating link  9   k  in the opposite direction (clockwise in  FIG. 1 ), causing the actuating link  9   h  to rotate downward into a horizontal state shown in  FIG. 7 . At this time, the operations of the upper links  9   b  and lower links  9   c  linked to the actuating link  9   h  cause the lower links  9   c  to rotate upward into a horizontal state as the actuating link  9   h  rotates downward. When the lower links  9   c  rotate upward, the foot member  9   f  separates from the contact surface M, allowing the wheel  5  to come into contact with the contact surface M. 
         [0036]    The wheelchair of the preferred embodiment also has a positioning mechanism  10  for positioning the wheel  5  in the separating position F in order to form the clearance K required for a person to get on and off the seat  2 . 
         [0037]    An interlocking mechanism  11  is also provided for enabling the positioning mechanism  10  when the wheel  5  is elevated and disabling the positioning mechanism  10  when the wheel  5  is resting on the contact surface M. 
         [0038]    As shown in  FIG. 6 , the positioning mechanism  10  includes a mounting piece  10   a  mounted on the frame  1 ; a support piece  10   b  mounted on the wheel side of the mounting piece  10   a ; a sliding piece  10   c  mounted on the bottom side of the mounting piece  10   a  so as to be capable of sliding in a direction toward and away from the wheel  5 ; a support cylinder  10   d  mounted on the bottom of the support piece  10   b ; a spring  10   e  disposed in the support cylinder  10   d ; a positioning pin  10   f  mounted in the support cylinder  10   d  and urged toward the wheel  5  by the spring  10   e , the base end of the positioning pin  10   f  being engaged with the sliding piece  10   c ; a cam plate  10   g  mounted on the outer lower link  9   c ; an actuating roller  10   h  rotatably mounted on the sliding piece  10   c ; a receiving pin  10   i  mounted in the remaining section  5   b  of the wheel  5  at a position opposing the positioning pin  10   f  when the wheel  5  is in the separating position F, the end of the receiving pin  10   i  having a sloped surface that approaches the positioning ping  10   f  toward the center of the same end; and a positioning hole  10   j  formed in the receiving pin  10   i  for receiving a tip end portion of the positioning pin  10   f.    
         [0039]    With this construction, when the foot member  9   f  separates from the contact surface M, placing the wheel  5  in contact with the contact surface M, as shown in  FIGS. 1 ,  6 , and  7 , the cam plate  10   g  pulls the actuating roller  10   h  in a direction away from the wheel  5 . At this time, the positioning pin  10   f  is retracted from the positioning hole  10   j , allowing the wheel  5  to roll freely on the ground surface. 
         [0040]    When the foot member  9   f  is placed in contact with the contact surface M so as to lift the wheel  5  off the contact surface M, as shown in  FIGS. 2 ,  3 ,  4 , and  5 , the cam plate  10   g  is separated from the actuating roller  10   h , and the positioning pin  10   f  protrudes toward the wheel  5  by the urging force of the spring  10   e . At this time, the wheel  5  can be freely rotated. As the operator rotates the wheel  5  to a position at which the positioning hole  10   j  opposes the positioning pin  10   f  (separating position F), the positioning pin  10   f  slides over the sloped surface formed on the end of the receiving pin  10   i  and is fittingly inserted into the positioning hole  10   j , as shown in  FIG. 4 . With the positioning pin  10   f  fitted into the positioning hole  10   j , the wheel  5  is fixed in the separating position F. 
         [0041]    The wheelchair of the preferred embodiment is also provided with a locking mechanism  12  for preventing the wheel  5  from rotating when the wheel  5  is in the separating position F. As shown in  FIGS. 1 ,  8 ,  9 , and  10 , the locking mechanism  12  has a rotary plate  12   a  with three crescent-shaped sliding holes  12   b  formed therein. The rotary plate  12   a  is mounted on the hub  5   c  of the wheel  5 , which is fixed to the frame  1 , by three sliding pins  12   c  inserted through respective sliding holes  12   b . The rotary plate  12   a  can swivel on the hub  5   c  within the range that the sliding pins  12   c  can slide within the sliding holes  12   b.    
         [0042]    The locking mechanism  12  also includes a fan-shaped plate  12   d  shaped substantially like a folding fan that is fixed to the rotary plate  12   a ; a guide rail  12   e  having a semicircular arc shape that is fixed to the outer edge of the fan-shaped plate  12   d ; and a guide roll  12   f  mounted on the removable section  5   a  of the wheel  5  at a position for contacting the inner surface of the guide rail  12   e  (see  FIG. 1 ). With this construction, the rotary plate  12   a  can pivot freely on the wheel  5  with the sliding pins  12   c  fitted in the sliding holes  12   b  and the guide roll  12   f  slidingly contacting the guide rail  12   e . Specifically, the fan-shape plate  12   d  can pivotably rotate between a mounting position D as shown in  FIG. 9  and a locking position G as shown in  FIG. 2 . 
         [0043]    As shown in  FIG. 8 , the locking mechanism  12  also includes a sliding cylinder  12   g  mounted on the wheel  5 ; a locking pin  12   h  slidably disposed in the sliding cylinder  12   g ; and a spring  12   i  disposed in the sliding cylinder  12   g  for urging the locking pin  12   h  toward the fan-shaped plate  12   d . An operating pin  12   k  having a knob  12   j  on one end thereof is disposed in the fan-shaped plate  12   d  and is capable of sliding in a direction toward and away from the wheel  5 . A spring  12   l  is provided for urging the operating pin  12   k  toward the wheel  5 . The operating pin  12   k  is formed with a groove  12   r  which is selectively engaged with a groove  13   d  described later. 
         [0044]    The locking mechanism  12  also includes a receiving pin  12   n  provided in the removable section  5   a  of the wheel  5 . The receiving pin  12   n  has a positioning hole  12   m  formed therein for receiving a tip end portion of the operating pin  12   k  when the fan-shape plate  12   d  is positioned at the locking position G as shown in  FIG. 2 . 
         [0045]    The locking mechanism  12  also has a receiving pin  12   p  provided in the remaining section  5   b  of the wheel  5  (see  FIG. 12 ). The receiving pin  12   p  has a positioning hole  12   o  for receiving the tip end portion of the operating pin  12   k  when the fan-shape plate  12   d  is positioned at the mounting position D as shown in  FIGS. 9 and 13 . 
         [0046]    A rail cam  12   q  is formed on the fan-shaped plate  12   d  for forcing the locking pin  12   h  back in the sliding cylinder  12   g  against the elastic force of the spring  12   i  (see  FIG. 10 ). The locking ping  12   h  is capable of engaging the locking hole  5   e  of the fixing disc  5   d.    
         [0047]    When the fan-shape plate  12   d  is positioned at the locking position G shown in  FIGS. 2 and 8 , the operating pin  12   k  is fitted into the positioning hole  12   m . While the wheel  5  is in the separating position F, the operator grips the knob  12   j  and pulls the operating pin  12   k  out of the positioning hole  12   m . In this state, the operator rotates the fan-shaped plate  12   d  clockwise in  FIG. 2  so that the fan-shaped plate  12   d  rotates from the locking position G shown in  FIGS. 2 and 8  to the mounting position D shown in  FIG. 9 . 
         [0048]    When the operator releases the knob  12   j  at this position, the rotary plate  12   a  urges the operating pin  12   k  toward and into the positioning hole  12   o  formed in the receiving pin  12   p  (see  FIG. 12 ), thereby fixing the position of the fan-shaped plate  12   d . When the fan-shaped plate  12   d  is rotated in this way, the rail cam  12   q  forces the locking pin  12   h  back against the spring  12   i  so that the locking pin  12   h  is fitted into the locking hole  5   e  formed in the fixing disc  5   d , as shown in  FIGS. 9 and 10 , thereby preventing rotation of the wheel  5 . 
         [0049]    From the state shown in  FIGS. 9 and 10 , the operator grips the knob  12   j  and pulls the operating pin  12   k  out from the positioning hole  12   o . In this state, the operator can rotate the fan-shaped plate  12   d  counterclockwise in  FIG. 9  to the position shown in  FIG. 2 . At this time, the spring  12   l  urges the operating pin  12   k  back into the positioning hole  12   m  formed in the receiving pin  12   n , thereby fixing the position of the fan-shaped plate  12   d . By rotating the fan-shaped plate  12   d  in this way, the rail cam  12   q  is separated from the locking pin  12   h , allowing the locking pin  12   h  to move from the state shown in  FIG. 10  to the state shown in  FIG. 8 . Specifically, the locking pin  12   h  slides along the surface of the rail cam  12   q  while the spring  12   i  pushes the locking pin  12   h  toward the fan-shaped plate  12   d  until the base end of the locking pin  12   h  is extracted from the locking hole  5   e . When the locking pin  12   h  is extracted from the locking hole  5   e , the wheel  5  is again free to rotate. 
         [0050]    The wheelchair according to the preferred embodiment also includes a safety mechanism  13 . The safety mechanism  13  functions to prevent the locking mechanism  12  from being disabled when the removable section  5   a  is separated from the remaining section  5   b  and to allow the locking mechanism  12  to be disabled when the removable section  5   a  is mounted on the remaining section  5   b.    
         [0051]    As shown in  FIGS. 9 ,  11 , and  12 , the safety mechanism  13  includes a pressing plate  13   a  mounted on the removable section  5   a ; a retaining plate  13   b  mounted on the remaining section  5   b ; an engaging member  13   c  disposed on the retaining plate  13   b  so as to be capable of sliding vertically, the engaging member  13   c  is formed with an engaging groove  13   d  which is capable of being detachably inserted into the groove  12   r  formed in the knob  12   j ; and a spring  13   e  disposed in the retaining plate  13   b  for urging the engaging groove  13   d  upward to be engaged in the groove  12   r.    
         [0052]    As illustrated in  FIGS. 13 ,  14 , and  15 , when the removable section  5   a  is separated from the remaining section  5   b , the pressing plate  13   a  is separated from the engaging member  13   c  and the engaging groove  13   d  formed in the engaging member  13   c  is engaged in the groove  12   r  by the urging force of the spring  13   e . This engagement prevents the operating pin  12   k  from being pulled out of the positioning hole  12   o  formed in the receiving pin  12   p  and, thus, prevents the fan-shaped plate  12   d  from being rotated. Hence, this construction prevents the operator from accidentally pulling the knob  12   j  of the operating pin  12   k  and extracting the base end of the locking pin  12   h  from the locking hole  5   e , thereby preventing the locking mechanism  12  from being unexpectedly disabled when the wheel  5  is in the separating position F and, thus, preventing the wheel  5  from unexpectedly rotating. 
         [0053]    Further, as shown in  FIGS. 9 ,  11 , and  12 , when the removable section  5   a  is mounted on the remaining section  5   b , the pressing plate  13   a  presses against the engaging member  13   c , pushing the engaging member  13   c  against the elastic force of the spring  13   e  so that the engaging groove  13   d  separates from the groove  12   r . Consequently, the operating pin  12   k  can be pulled outward, allowing the fan-shaped plate  12   d  to be rotated and the base end of the locking pin  12   h  to be extracted from the locking hole  5   e  for disabling the locking mechanism  12 . 
         [0054]    A removable section separating process will be described below. 
         [0055]    The wheelchair  1  is in a state as shown in  FIG. 1 . An operator pulls the handle  9   n  to lift the wheel  5  off the contact surface M so that the wheel  5  can be freely rotated. At this time, the cam plate  10   g  is away from the actuating roller  10   h  and the positioning pin  10   f  is in contact with the wheel  5  by the urging force of the spring  10   e . When the operator rotates the wheel  5  to be positioned at the separating position F, the positioning pin  10   f  is engaged with the receiving ping  10   i , thereby fixing the wheel  5  at the separating position F ( FIG. 3 ). 
         [0056]    The operator pulls the knob  12   j  from the receiving hole  12   o  of the removable section  5   a  and rotates the fan-shape plate  12   d  in clockwise direction. The fan-shape plate  12   d  is moved from the locking position G to the mounting position D. When the operator releases the knob  12   j  at the mounting position D, the operating pin  12   k  is engaged with the receiving pin  12   p  of the remaining section  5   b , and simultaneously the locking pin  12   h  is fitted into the locking hole  5   e  ( FIG. 10 ), thereby preventing the wheel  5  from freely rotating. 
         [0057]    In this state, the operator can separate the removable section  5   a  from the remaining section  5   b . Then, the pressing plate  13   a  is away from the engaging member  13   c , and the engaging groove  13   d  is engaged with the groove  12   r  so that the operator cannot pull the knob  12   j  ( FIGS. 14 , and  15 ). 
         [0058]    With the wheelchair according to the preferred embodiment described above, clearance K necessary for a person to get on and off the seat  2  can be formed using the wheel separation mechanism  7  to separate the fan-shaped removable section  5   a  from the remaining section  5   b . Thereafter, the removable section  5   a  can be adjoined with the remaining section  5   b  to allow the seated person use of the wheelchair. Thus, the wheelchair according to the preferred embodiment enables a hospital patient, physically disabled person, elderly person in assisted living, and the like to get on and off the wheelchair smoothly and easily. 
         [0059]    By providing the positioning mechanism  10  for fixing the wheel  5  in the separating position F, the operator can rotate the wheel  5  to the separating position F and fittingly insert the positioning pin  10   f  on the frame side of the positioning mechanism  10  into the positioning hole  10   j  on the wheel  5  side to fix the wheel  5  in the separating position F, as shown in  FIGS. 2 ,  3 , and  4 . Accordingly, the operator can easily fix the wheel  5  in the separating position F in order to form the clearance K required for getting on and off the seat  2 , thereby improving the operation for positioning the wheel  5  and, thus, enhancing convenience for the user. 
         [0060]    By providing the elevating mechanism  9  on the frame  1  for elevating the wheel  5  off the contact surface M, the operator can pull the operating link  9   k  using the handle  9   n  while the wheel  5  is resting on the contact surface M, as shown in  FIG. 7 , pushing the foot member  9   f  against the contact surface M to lift the wheel  5  off the contact surface M. While the wheel  5  is elevated off the contact surface M, the wheel  5  can freely rotate. Accordingly, the operator can easily rotate the wheel  5  into the separating position F for forming the clearance K required for getting on and off the seat  2 , thereby facilitating the operation for positioning the wheel  5  with the positioning mechanism  10 . 
         [0061]    With the interlocking mechanism  11  for enabling operations of the positioning mechanism  10  when the wheel  5  is elevated and for disabling operations of the positioning mechanism  10  when the wheel  5  is in contact with the contact surface M, the cam plate  10   g  pulls the actuating roller  10   h  away from the wheel  5  when the wheel  5  is in contact with the contact surface M, as shown in  FIG. 6 , thereby extracting the positioning pin  10   f  from the positioning hole  10   j . When the wheel  5  is elevated, the cam plate  10   g  separates from the actuating roller  10   h  so that the positioning pin  10   f  is fittingly inserted into the positioning hole  10   j  through the urging force of the spring  10   e  when the wheel  5  is in the separating position F, as shown in  FIG. 4 . Thus, the operation of the positioning mechanism  10  is enabled and disabled in association with the operations for raising and lowering the wheel  5 , thereby facilitating operations of the positioning mechanism  10 . 
         [0062]    Further, by providing the locking mechanism  12  for preventing rotation of the wheel  5  in the separating position F, the base end of the locking pin  12   h  is inserted into the locking hole  5   e  when the fan-shape plate  12   d  is positioned at the mounting position D, as shown in  FIG. 9 , preventing the wheel  5  from rotating. Accordingly, the wheel  5  can be reliably fixed in the separating position F for forming the clearance K required to get on and off the seat  2 . 
         [0063]    Further, with the safety mechanism  13  for preventing the locking mechanism  12  from being disabled when the removable section  5   a  is separated from the remaining section  5   b  and for allowing the locking mechanism  12  to be disabled when the removable section  5   a  is mounted on the remaining section  5   b , the pressing plate  13   a  is separated from the engaging member  13   c  when the removable section  5   a  is separated from the remaining section  5   b , as shown in  FIG. 14 , so that the engaging groove  13   d  of the engaging member  13   c  is engaged in the groove  12   r  through the urging force of the spring  13   e . This construction prevents the operating pin  12   k  from being pulled out of the positioning hole  12   o  formed in the receiving pin  12   p , thereby preventing the fan-shaped plate  12   d  from rotating. Hence, the operator is prevented from mistakenly pulling the knob  12   j  of the operating pin  12   k  and extracting the base end of the locking pin  12   h  from the locking hole  5   e , thereby preventing the locking mechanism  12  from being unexpectedly disabled when the wheel  5  is in the separating position F. Thus, the remaining section  5   b  of the wheel  5  is prevented from rotating when the removable section  5   a  is separated therefrom, enhancing operational safety. 
         [0064]    While the invention has been described in detail with reference to a specific embodiment thereof, it would be apparent to those skilled in the art that many modifications and variations may be made to the structures and design of the frame  1 , seat  2 , wheel separation mechanism  7 , elevating mechanism  9 , positioning mechanism  10 , interlocking mechanism  11 , locking mechanism  12 , and safety mechanism  13 , for example, without departing from the spirit of the invention, the scope of which is defined by the attached claims. 
         [0065]    The present invention according to the preferred embodiment can sufficiently attain the objectives described earlier for improving the prior art. 
         [0066]    In the embodiment described above, the separation mechanism  7  is provided only in the right wheel  5 . However, the separation mechanism  7  may be provided in at least one of wheels  5 . 
         [0067]    In the embodiment, the elevating mechanism  9  lifts the right wheel  5 . However, the elevating mechanism  9  may be modified to as to lift both right and left wheels  5 .