Patent Description:
An electric wheelchair in <CIT> can climb and descend stairs. The electric wheelchair in <CIT> includes main wheels arranged on both sides of a chair, support rods extending rearward from the chair, and auxiliary wheels positioned rearward of the main wheels. The main wheels are driven by a motor. Rear end parts of the support rods pivot up and down by actuators. The auxiliary wheels also pivot up and down by the actuators. The electric wheelchair can float the auxiliary wheels on the stairs and climb and descend the stairs while supporting the chair with the main wheels and the support rods.

One can consider that a front support rod extending frontward is included such that the chair does not undergo forward falling-down during stair descent. The front support rod can support the chair when the chair is inclined frontward. In such a case, there is a concern that, when both the front support rod and the rear support rod result in touching the ground to cause the main wheel to float, the entire electric wheelchair slips on the stairs. The present specification provides a technology that enables, for an electric wheelchair having support rods at the front and the rear of a chair, both supporting rods not to touch the ground during stair descent.

An electric wheelchair disclosed by the present specification includes: a chair; main wheels arranged on both sides of the chair; a front support rod; a rear support rod; a road surface sensor; and a controller. The main wheels are driven by a motor. The front support rod extends frontward from the chair and has a front end part that pivots up and down by an actuator. The rear support rod extends rearward from the chair and has a rear end part that pivots up and down by an actuator. When the electric wheelchair climbs or descends stairs, the road surface sensor senses a shape of the stairs. When the electric wheelchair descends stairs, the controller determines a position of the front end part of the front support rod as follows. That is, the controller determines the position of the front end part based on one of a slope angle formed by a plane obtained by connecting edges of steps of the stairs and a horizontal plane and an edge position angle formed by a line connecting an edge, out of the edges of the steps of the stairs, that is nearest to a center of the main wheels and the main wheel center and a vertical direction. Each "edge of the steps" denotes a right angle portion at the upper corner of each step of the stairs.

By the position of the front end part being determined as above, the front end part is held at a position above the edge of the stairs. When the electric wheelchair is inclined frontward to cause the rear support rod to float, the front end part of the front support rod touches the stairs and prevents the chair from rotating frontward. At this time, the front end part and the main wheel touch the ground and the entire electric wheelchair does not slip or fall down the stairs.

Details of the technology disclosed by the present specification and further improvements are described in "DETAILED DESCRIPTION OF EMBODIMENTS" below.

An electric wheelchair <NUM> of an embodiment will be described with reference to the drawings. <FIG> shows a lateral view of the electric wheelchair <NUM> of an embodiment. The electric wheelchair <NUM> of an embodiment includes a chair <NUM>, main wheels <NUM>, and a motor <NUM>. The main wheels <NUM> are arranged on both sides of the chair <NUM> and are driven by the motor <NUM>. Note that, in <FIG>, for better understanding of the structure of the electric wheelchair <NUM>, the main wheel <NUM> is drawn with broken lines, and devices positioned behind the main wheel <NUM> (devices that are normally hidden by the main wheel <NUM> and cannot be seen) are drawn with solid lines.

The electric wheelchair <NUM> further includes a front support rod <NUM>, a rear support rod <NUM>, and actuators <NUM>, <NUM>. The front support rod <NUM> extends frontward from the chair <NUM>. A rear end of the front support rod <NUM> is pivotally supported on a pivot <NUM>. The actuator <NUM> is attached between the chair <NUM> and the front support rod <NUM>. The actuator <NUM> is of linear motion type, and when expanding and contracting, causes a front end part 14a of the front support rod <NUM> to pivot up and down. To the tip of the support rod <NUM>, a rotatable auxiliary wheel is attached.

Signs "14a_U" and "14a_L" in <FIG> represent a movable range of the front support rod <NUM>. A front end part 14a_U represents the position of an upper limit of the front support rod <NUM> (that is, an upper limit position of the front end part 14a). A front end part 14a_L represents the position of a lower limit of the front support rod <NUM> (that is, a lower limit position of the front end part 14a). By the front support rod <NUM> pivoting, the front end part 14a changes between the position indicated by the front end part 14a_U and the position indicated by the front end part 14a_L in <FIG>.

The front support rod <NUM> is a device for preventing forward falling-down of the electric wheelchair <NUM> (chair <NUM>). The front end part 14a_L can be positioned below a horizontal floor F such that, when the electric wheelchair <NUM> is descending a stair, the front end part 14a can be positioned right above the step below the stair.

The rear support rod <NUM> extends rearward from the chair <NUM>. A front end of the rear support rod <NUM> is pivotally supported on the pivot <NUM>. The actuator <NUM> is attached between the chair <NUM> and the rear support rod <NUM>. The actuator <NUM> is of linear motion type, and when expanding and contracting, causes a rear end part 15a of the rear support rod <NUM> to pivot up and down. The pivot <NUM> is positioned rearward of a shaft 12a of the main wheel <NUM> and on the lower side of the shaft 12a. In other words, the pivot <NUM> is positioned behind and below the shaft 12a.

The rear end part 15a of the rear support rod <NUM> has a shape of a sled. The center of gravity (including the weight of a seated user) of the electric wheelchair <NUM> is positioned rearward of a center (shaft 12a) of the main wheel <NUM>. Therefore, the rear end part 15a of the rear support rod <NUM> comes into contact with the floor F. By the rear end part 15a being moved up and down, a target posture angle of the chair <NUM> (rotation angle of the chair <NUM> around the shaft 12a of the main wheel <NUM>) can be adjusted.

The motor <NUM> and the actuators <NUM>, <NUM> are controlled by a controller <NUM>. The controller <NUM> is built in the chair <NUM>. Moreover, various sensors <NUM> are also attached to the chair <NUM>. The sensors <NUM> include a vehicle speed sensor that measures a speed of the electric wheelchair <NUM>, an angle sensor that measures a posture angle of the chair <NUM>, a road surface sensor that senses a shape of a surface that the electric wheelchair <NUM> is travelling on, and the like. When the electric wheelchair <NUM> climbs and descends stairs, the road surface sensor senses a shape of the stairs. Illustration of the individual sensors is omitted.

The electric wheelchair <NUM> skillfully uses the front support rod <NUM> and the rear support rod <NUM> and can prevent falling-down in descending the stairs.

When the electric wheelchair <NUM> descends stairs, the controller <NUM> determines a position of the front end part 14a based on one of a slope angle and an edge position angle. The controller <NUM> controls the front support rod <NUM> (actuator <NUM>) such that the determined position of the front end part 14a is attained. Hereinafter, the position of the front end part 14a is referred to as "front end part position". A position of the rear end part 15a of the rear support rod <NUM> is referred to as "rear end part position".

Referring to <FIG> and <FIG>, a front end part position determination process based on the slope angle is described. A slope angle As denotes an angle formed by a plane (slope plane SL) obtained by connecting a plurality of edges <NUM> of stairs <NUM> and a horizontal plane HL (refer to <FIG>). As shown in <FIG>, each "edge <NUM> of stairs" denotes a right angle part at an upper corner of each stair of the stairs <NUM>. In <FIG>, some of the components are omitted for simplified drawing of the electric wheelchair <NUM>.

A target posture angle At of the chair <NUM> is herein defined. The target posture angle At denotes an angle formed by an axis (front axis Cf) oriented frontward to be parallel to a seat surface of the chair <NUM> and the horizontal plane HL. Note that the axis perpendicular to the seat surface is referred to as perpendicular axis Cv (refer to <FIG>). The origin where the front axis Cf and the perpendicular axis Cv intersect is positioned at a center Ce of the main wheel <NUM>. The front axis Cf and the perpendicular axis Cv constitutes a local coordinate system fixed to the chair <NUM>.

As mentioned earlier, the posture angle of the chair <NUM> is adjusted by the position (rear end part position) of the rear end part 15a of the rear support rod <NUM>. The controller <NUM> controls the rear support rod <NUM> such that an actual posture angle of the chair <NUM> coincides with the target posture angle At.

The controller determines the front end part position, with a total value (As + At) of the slope angle As and the target posture angle At being as a parameter, such that the front end part 14a maintains a predefined distance from the slope plane SL.

The front end part position that maintains the predetermined distance from the slope plane SL depends on a geometric structure of the electric wheelchair <NUM>. Therefore, the front end part position that maintains the predetermined distance from the slope plane SL is predetermined in a form of a map (or a form of a function) that outputs the front end part position with respect to an input value (As + At), and is stored in the controller <NUM>. <FIG> shows an example of the relationship of the front end part position relative to the total value of the slope angle As and the target posture angle At. The axis of ordinates denotes the front end part position. The front end part position of the axis of ordinates is represented by a percentage with the upper limit position (position of the front end part 14a_U) and the lower limit position (position of the front end part 14a_L) of the front support rod <NUM> mentioned above being as <NUM> [%] and <NUM> [%], respectively. As mentioned earlier, the front end part position that maintains the predetermined fixed distance from the slope plane SL depends on the geometric structure of the electric wheelchair <NUM>, and is predetermined as exemplarily shown in <FIG>.

The front end part position is determined with respect to the total value of the target posture angle At and the slope angle As. Therefore, when the actual posture angle of the chair <NUM> deviates from the target posture angle At and the chair <NUM> inclines frontward, the front end part 14a touches the stair <NUM>, which prevents forward falling-down of the chair <NUM>.

Referring to <FIG> and <FIG>, a determination process of the front end part position based on the edge position angle is described. An edge position angle Ag denotes an angle (refer to <FIG>) formed by a line connecting the nearest edge (edge 91a in <FIG>) to the center Ce of the main wheel <NUM> in the horizontal direction and the center Ce and the vertical direction VL. The nearest edge 91a to the center Ce of the main wheel <NUM> in the horizontal direction is referred to as the near edge 91a for convenience of description. The controller <NUM> determines the front end part position such that a predetermined distance is maintained between the front end part 14a and the near edge 91a in the vertical direction. This front end part position depends on the edge position angle Ag.

The front end part position that maintains the predetermined distance from the near edge 91a in the vertical direction depends on the geometric structure of the electric wheelchair <NUM>. The front end part position that maintains the predetermined distance is predetermined in a form of a map (or a form of a function) with the edge position angle Ag being as an input value, and is stored in the controller <NUM>. <FIG> shows an example of the relationship of the front end part position with respect to the edge position angle Ag. The numerical values on the axis of ordinates mean the same as those on the axis of ordinates in the graph of <FIG>.

During the electric wheelchair <NUM> descending the stairs, the controller <NUM> determines the front end part position based on the total value of the target posture angle At and the slope angle As. This front end part position is referred to as slope front end part position. Simultaneously, the controller <NUM> also determines the front end part position based on the edge position angle Ag. This front end part position is referred to as edge front end part position. The controller <NUM> compares the slope front end part position and the edge front end part position and selects the higher one. The controller <NUM> controls the front support rod <NUM> (actuator <NUM>) such that the selected front end part position is attained. In predetermined control cycles, the controller <NUM> repeats the determination of the front end part position and the control of the front support rod <NUM>.

With reference to <FIG>, examples of the controller <NUM> selecting one of the slope front end part position and the edge front end part position are described. In <FIG>, the near edge 91a is positioned rearward of the center Ce of the main wheel <NUM>, and the edge position angle is an angle Ag_a. The slope angle is the angle As. At this time, the slope front end part position (position of a front end part 14a_sl) is higher than the edge front end part position (position of a front end part 14a_eg). The controller <NUM> selects the slope front end part position (position of the front end part 14a_sl) and controls the front support rod <NUM> (actuator <NUM>) such that this position is attained.

In <FIG>, the electric wheelchair <NUM> advances a little from the state of <FIG>, and the near edge moves to an edge 91b. The near edge 91b is positioned frontward of the center Ce of the main wheel <NUM>, and the edge position angle is an angle Ag_b. The slope angle is the angle As. At this time, the edge front end part position (position of the front end part 14a_eg) is higher than the slope front end part position (position of the front end part 14a_sl). The controller <NUM> selects the edge front end part position (position of the front end part 14a_eg) and controls the front support rod <NUM> (actuator <NUM>) such that this position is attained. Accordingly, if the posture angle of the chair <NUM> deviates from the target posture angle, resulting in the frontward inclination, the front end part 14a comes into contact with the stairs, which prevents the forward falling-down.

With reference to <FIG>, control of the rear support rod <NUM> is described. In <FIG>, a rear end part 15a_U denotes the position of an upper limit of the rear support rod <NUM> (an upper limit position of the rear end part 15a), and a rear end part 15a_L denotes the position of a lower limit of the rear support rod <NUM> (a lower limit position of the rear end part 15a).

As mentioned earlier, the position of the rear support rod <NUM> defines the posture of the chair <NUM>. The controller <NUM> controls the rear support rod <NUM> (actuator <NUM>) such that the target posture angle is attained. In place of such control, the controller <NUM> may determine the rear end part position (position of the rear end part 15a) of the rear support rod <NUM> based on a touching point angle Ast and may control the rear support rod <NUM> (actuator <NUM>) such that the determined rear end part position is attained. Here, the touching point angle Ast denotes an angle formed by a line connecting the edge that is in contact with the main wheel <NUM> (an edge 91c in the case of <FIG>) and the center Ce of the main wheel <NUM> and the perpendicular axis Cv. The perpendicular axis Cv denotes the axis perpendicular to the seat surface of the chair <NUM>. The edge 91c in contact with the main wheel <NUM> is referred to as touching edge 91c for convenience of description. The controller <NUM> determines the rear end part position such that a predetermined distance is maintained between a line that passes through the touching edge 91c and is in contact with the wheel <NUM> and the rear end part position.

The rear end part position that maintains the predetermined distance between the line which passes through the touching edge 91c and is in contact with the wheel <NUM> and the rear end part position depends on the touching point angle Ast. Therefore, such a rear end part position is predetermined in a form of a map (or a form of a function) that outputs the rear end part position with respect to an input value (the touching point angle Ast), and is stored in the controller <NUM>. <FIG> shows an example of the relationship of the rear end part position relative to the touching point angle Ast.

The axis of ordinates in <FIG> denotes the rear end part position. The front end part position of the axis of ordinates is represented by a percentage with the upper limit position (position of the rear end part 15a_U) and the lower limit position (position of the rear end part 15a_L) of the rear support rod <NUM> mentioned above being as <NUM> [%] and <NUM> [%], respectively. As mentioned earlier, the rear end part position that maintains the predetermined distance between the line which passes through the touching edge 91c and is in contact with the wheel <NUM> and the rear end part position depends on the geometric structure of the electric wheelchair <NUM> and the touching point angle Ast, and is predetermined as exemplarily shown in <FIG>.

The rear end part position that is targeted by the controller <NUM> takes a value obtained by adding "gain × posture error" to the current rear end part position. The controller <NUM> controls the rear support rod <NUM> (actuator <NUM>) such that the targeted rear end part position is attained.

The electric wheelchair <NUM> includes a joystick that the seated user manipulates. When the joystick is tilted frontward, the electric wheelchair <NUM> goes frontward, and when the joystick is tilted rearward, the electric wheelchair <NUM> goes rearward. When the joystick is at a neutral position, the electric wheelchair <NUM> stops. When an angle at which the joystick is tilted frontward is increased, an advancing speed increases. When an angle at which the joystick is tilted rearward is increased, a reversing speed of the electric wheelchair <NUM> increases.

The electric wheelchair <NUM> needs to decelerate or stop against manipulation of the user for safety in accordance with the situation. The controller <NUM> determines the speed of the electric wheelchair <NUM> with the tilt of the joystick multiplied by predetermined gains. There are some kinds of gains. A gain A is a gain in accordance with a posture control error, and is set to be smaller as the posture control error is larger. A gain B is a gain in accordance with the slope angle, and is set to be smaller as the slope angle is larger. A gain C is a gain in accordance with a control error of the rear support rod <NUM>, and is set to be smaller as the control error is larger. A gain D is a gain in accordance with a roll posture error of the electric wheelchair <NUM>, and is set to be smaller as the posture error is larger. A gain E is a gain in accordance with a height of steps, and is zero when the steps are larger than a predetermined threshold. When the steps are smaller than the threshold, the gain E is set to "<NUM>". The controller <NUM> determines the speed of the electric wheelchair <NUM> by the tilt of the joystick being multiplied by the aforementioned gains A to E. When the steps are larger than the predetermined threshold, the gain E is zero and the electric wheelchair <NUM> does not move.

Points of attention regarding the technology described for the embodiment are mentioned. The shape of stairs can be measured by a LiDAR sensor, a 3D image sensor, a plurality of distance sensors, or the like. LiDAR is an abbreviation of "Light Detection And Ranging". The LiDAR sensor radiates laser in a plurality of directions and measures distances from an obstacle (steps) in the directions. The outer shape of the obstacle (steps) is acquired based on the measured distances in the directions. The 3D image sensor captures images of the stairs with two cameras and measures the shape of the stairs based on the principle of stereoscopy. The shape of the stairs can also be measured by a sensor having a plurality of distance sensors arranged so as to radiate parallel laser beams.

The controller <NUM> may estimate the edge positions of the stairs with respect to the body of the electric wheelchair <NUM>, the inclination angle of the stairs (the slope angle mentioned above), and the touching positions of the main wheel, and with a control map for handling those, may control the front support rod <NUM> and the rear support rod <NUM>.

The electric wheelchair <NUM> may have a contact determining apparatus that determines whether the front and rear support rods <NUM>, <NUM> are in contact with the ground surface, and the controller <NUM> may change the control depending on whether or not the front and rear support rods <NUM>, <NUM> are in contact with the ground surface.

The controller <NUM> may reduce the speed of the electric wheelchair <NUM> in accordance with a control error for the posture of the front and rear support rods <NUM>, <NUM>.

The controller <NUM> may set the speed of the electric wheelchair <NUM> to zero when the height of steps in the travelling direction of the electric wheelchair <NUM> is larger than the radius of the main wheel <NUM>. The "travelling direction" includes the case of advancing and the case of reversing.

The electric wheelchair <NUM> carries a power supply for the motor <NUM>, the actuators <NUM>, <NUM>, the controller <NUM>, and the sensors <NUM> beneath the chair <NUM> (or in the back of the chair <NUM>), illustration of the power supply being omitted.

The front support rods <NUM> may be provided on both sides of the chair <NUM>, or only on one side of the chair <NUM>, the front support rod <NUM> may be provided. In the latter case, a crossbar is attached to the tip part of the front support rod, and thereby, the main wheels are stably floated with the front support rod and the rear support rod. The rear support rods may also be disposed on both sides of the chair <NUM>, or at the center of the chair <NUM> in the right-left direction, one rear support rod may be disposed.

Claim 1:
An electric wheelchair (<NUM>) comprising:
a chair (<NUM>); and
main wheels (<NUM>) that are arranged on both sides of the chair (<NUM>) and are configured to be driven by a motor (<NUM>); and
a front support rod (<NUM>) extending frontward from the chair (<NUM>) and having a front end part (14a) that pivots up and down;
a rear support rod (<NUM>) extending rearward from the chair (<NUM>) and having a rear end part (15a) that pivots up and down;
a road surface sensor (<NUM>) for sensing a shape of stairs (<NUM>), when the electric wheelchair (<NUM>) climbs or descends the stairs (<NUM>); and
a controller (<NUM>) for controlling the front support rod (<NUM>), the rear support rod (<NUM>), and the main wheels (<NUM>), wherein:
a center of gravity of the electric wheelchair is positioned rearward of a shaft (12a) of the main wheels (<NUM>); and
the controller (<NUM>) is configured so that, when the electric wheelchair (<NUM>) descends the stairs (<NUM>), the controller (<NUM>) determines a position of the front end part (14a) based on one of a slope angle (As) formed by a plane (SL) obtained by connecting edges (<NUM>) of steps of the stairs (<NUM>) and a horizontal plane (HL) and an edge position angle (Ag) formed by a line connecting an edge (<NUM>), out of the edges (<NUM>) of the steps of the stairs (<NUM>), that is nearest to a center (Ce) of the main wheels (<NUM>), and the center (Ce) of the main wheels (<NUM>), and a vertical direction (VL).