Patent Publication Number: US-2015066276-A1

Title: Inverted two-wheel apparatus

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2013-176425 filed on Aug. 28, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inverted two-wheel apparatus. 
     2. Description of Related Art 
     An inverted two-wheel apparatus, which travels while maintaining the inverted state, is known. 
     For example, WO 2011/108029 discloses an inverted two-wheel apparatus that includes a motor that drives the wheels, a control unit that generates a torque command value for controlling a torque generated by the driving of a motor, and attitude detection means that detects attitude information on the inverted two-wheel apparatus. 
     Incidentally, a rider who is going to ride an inverted two-wheel apparatus sometimes tilts the apparatus too much to the rider side. This causes the inverted two-wheel apparatus, disclosed in WO 2011/108029, to travel toward the rider to maintain the inverted state. This traveling sometimes causes the inverted two-wheel apparatus to come in contact with, and keep on pushing, the foot of the rider. 
     SUMMARY OF THE INVENTION 
     The present invention provides an inverted two-wheel apparatus that does not keep on pushing the foot of the rider even if the rider, who is going to ride the apparatus, tilts the apparatus too much to the rider side. 
     A first aspect of the present invention relates to an inverted two-wheel apparatus. An inverted two-wheel apparatus includes a motor that drives wheels; an angular velocity control unit that generates a target angular velocity for controlling an angular velocity of the motor; an angular velocity detection unit that detects a detected angular velocity of the motor; and a stop control unit that inhibits a rotation of the motor if a difference between the target angular velocity and the detected angular velocity is equal to or larger than an angular velocity threshold. 
     According to the aspect described above, the inverted two-wheel apparatus does not keep on pushing the foot of the rider even if the rider, who is going to ride the apparatus, tilts the apparatus too much to the rider side. 
     On the other hand, a second aspect of the present invention relates to an inverted two-wheel apparatus. An inverted two-wheel apparatus includes a motor that drives wheels; a torque sensor that detects a detected torque of the motor; and a stop control unit that differentiates the detected torque to calculate a detected torque derivative and, if the detected torque derivative is equal to or larger than a torque derivative threshold, inhibits a rotation of the motor. 
     According to the aspect described above, the inverted two-wheel apparatus does not keep on pushing the foot of the rider even if the rider, who is going to ride the apparatus, tilts the apparatus too much to the rider side. 
     The inverted two-wheel apparatus in the aspects described above does not keep on pushing the foot of the rider even if the rider, who is going to ride the apparatus, tilts the apparatus too much to the rider side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a side view of an inverted two-wheel apparatus in a first embodiment of the present invention; 
         FIG. 2  is a configuration diagram of the inverted two-wheel apparatus in the first embodiment of the present invention; 
         FIG. 3  is a flowchart showing a control method in the first embodiment of the present invention; 
         FIGS. 4A to 4G  are schematic diagrams showing the control method in the first embodiment of the present invention; 
         FIG. 5  is a graph showing angular velocity versus time; 
         FIG. 6  is a configuration diagram of an inverted two-wheel apparatus in a second embodiment of the present invention; and 
         FIG. 7  is a flowchart showing a control method in the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     An inverted two-wheel apparatus in a first embodiment is described below with reference to  FIG. 1 .  FIG. 1  is a side view of the inverted two-wheel apparatus in the first embodiment. 
     As shown in  FIG. 1 , an inverted two-wheel apparatus  1  includes a wheel unit  2 , a platform unit  3 , and a handle  4 . 
     The wheel unit  2  includes wheels  21 , a motor  22 , and a motor rotation angle sensor  23 . The motor  22  drives the wheels  21 . The motor rotation angle sensor  23  can detect the angle of the wheels  21 . The motor rotation angle sensor  23  is equipped, for example, with a resolver and an encoder. The motor rotation angle sensor  23  calculates the angular velocity ω by differentiating the detected angles (see  FIG. 2 ) and outputs the signal about the angular velocity ω. 
     The platform unit  3  includes steps  31 R and  31 L, an attitude angle detection sensor  32 , and load sensors  33 L and  33 R. The step  31 R, provided above the wheel unit  2 , is a support plate for supporting the right foot of a rider. The step  31 L, provided above the wheel unit  2 , is a support plate for supporting the left foot of the rider. The attitude angle detection sensor  32  is a sensor for detecting the attitude angle of the platform unit  3  and the handle  4 . The attitude angle detection sensor  32  is a sensor such as a gyro sensor or an acceleration sensor. The attitude angle detection sensor  32  detects a detected attitude angle η (see  FIG. 2 ) and outputs the signal about the detected attitude angle The load sensor  33 L detects the load placed on the step  31 L, and the load sensor  33 R detects the load placed on the step  31 R. The load sensors  33 L and  33 R can detect the center of gravity, pitch angle, and roll angle of the load placed on the steps  31 L and  31 R. The load sensors  33 L and  33 R generate the signal about the load information m (see  FIG. 2 ). The load information m includes information about the magnitude and the center of gravity of the load placed on the steps  31 L and  31 R. The load information m may also include information such as the pitch angle and the roll angle of the steps  31 L and  31 R. 
     The handle  4  includes a shaft unit  41  that extends upward from the platform unit  3  and a hand grip unit  42  that is supported at the top end of the shaft unit  41 . The hand grip unit  42  has a shape that can be gripped by both hands of a rider. The shape of the hand grip unit  42  may be changed so that a rider holds it with his or her feet. The length of the shaft unit  41  may be changed as necessary according to the change in the shape of the hand grip unit  42 . 
     Next, the configuration of the inverted two-wheel apparatus is described with reference to  FIG. 2 .  FIG. 2  is a configuration diagram of the inverted two-wheel apparatus in the first embodiment. 
     As shown in  FIG. 2 , a control unit  50  includes a target generation unit  51 , a deviation calculation unit  52 , a feedback compensation control unit  53 , a motor driver  54 , and a determination unit  55 . In addition, the control unit  50  may include a step-on-platform start detection unit  56  that detects the start of rider&#39;s step-on-platform action and a step-on-platform completion detection unit  57  that detects the completion of rider&#39;s step-on-platform action. The control unit  50  is connected to a power supply, not shown, and electric current is supplied to the control unit  50  as necessary. The control unit  50  includes an operation circuit that has a central processing unit (CPU), and a storage device that has a program memory, a data memory, and other memories such as a random access memory (RAM) and a read-only memory (ROM). 
     The target generation unit  51  receives the signal about the load information m from the load sensors  33 L and  33 R. Based on the load information m, the target generation unit  51  calculates the target angular velocity ω* and the target attitude angle η* and outputs the signal about the target angular velocity ω* and the target attitude angle η*. 
     The deviation calculation unit  52  receives the signal about the target angular velocity ω* and the target attitude angle η* from the target generation unit  51 . The deviation calculation unit  52  also receives the signal about the detected angular velocity ω from the motor rotation angle sensor  23 , and the detected attitude angle η from the attitude angle detection sensor  32 . The deviation calculation unit  52  calculates the difference between the target angular velocity ω* and the detected angular velocity w (deviation angular velocity Δω) and the difference between the target attitude angle η* and the detected attitude angle η (deviation attitude angle Δη) and outputs the signal about the deviation angular velocity Δω and the deviation attitude angle Δη. 
     The feedback compensation control unit  53  includes the determination unit  55 . The determination unit  55  determines whether the deviation angular velocity Δω is equal to or higher than, or lower than, the angular velocity threshold Δω1. The angular velocity threshold Δω1 is stored in advance in the determination unit  55 . The feedback compensation control unit  53  receives the signal about the deviation angular velocity Δω and the deviation attitude angle Δη. The feedback compensation control unit  53  outputs the signal about the target torque T*. 
     If the deviation angular velocity Δω is lower than the angular velocity threshold Δω1, the feedback compensation control unit  53  outputs the signal about the inverted control torque Tt* as the signal about the target torque T*. The inverted control torque Tt* is a torque value for allowing the inverted two-wheel apparatus  1  to travel based on the load information m while maintaining the inverted state. That is, the inverted control torque Tt* is a torque value for performing the inverted control. 
     On the other hand, if the deviation angular velocity Δω is equal to or higher than the angular velocity threshold Δω1, the feedback compensation control unit  53  outputs the signal about the stop torque Ts* as the signal about the target torque T*. The stop torque Ts* is a torque value for controlling the torque of the motor  22  such that the rotation of the wheels  21  is stopped. That is, the stop torque Ts* is a torque value for performing the stop control. The stop torque Ts* may be a torque value the direction and magnitude of which inhibits the inverted two-wheel apparatus  1  from traveling toward the rider side. 
     The motor driver  54  receives the signal about the target torque T* from the feedback compensation control unit  53 . The motor driver  54  supplies electric current to the motor  22  based on the signal about the target torque T*. 
     The motor  22  receives electric current from the motor driver  54  to drive the wheels  21 . The motor rotation angle sensor  23  detects the angle of the wheels  21 , calculates the detected angular velocity ω, and outputs the signal about the detected angular velocity ω to the deviation calculation unit  52 . The attitude angle detection sensor  32  detects the detected attitude angle η and outputs the signal about the detected attitude angle η to the deviation calculation unit  52 . 
     Control Method 
     Next, with reference to  FIGS. 3 to 5 , the control method for controlling the inverted two-wheel apparatus in the first embodiment is described.  FIG. 3  is a flowchart showing the control method in the first embodiment.  FIG. 4A to 4G  are schematic diagrams showing the control method in the first embodiment.  FIG. 5  is a graph showing angular velocity versus time. 
     As shown in  FIGS. 4A to 4C , the start of the step-on-platform action is detected (step-on-platform start detection step S 1 ). More particularly, as shown in  FIG. 4A , a rider holds the hand grip unit  42  with both hands. Next, as shown in  FIG. 4B , the rider changes the attitude angle of the inverted two-wheel apparatus  1  so that the rider can easily place one foot on one of the steps  31 L and  31 R. For example, the rider changes the attitude angle of the inverted two-wheel apparatus  1  so that the longitudinal direction of the shaft unit  41  stays approximately upright. Next, as shown in  FIG. 4C , one of the steps  31 L and  31 R supports one foot of the rider and detects the load (step-on-platform start detection step S 1 : YES). Note that the step-on-platform start detection step S 1  of this control method may be executed by the step-on-platform start detection unit  56 . More specifically, based on the load information indicating that the load is placed on only one of the steps  31 L and  31 R, the step-on-platform start detection unit  56  may determine that the rider has started the step-on-platform action. 
     Next, the inverted control is started (inverted control step S 2 ). In addition, the motor rotation angle sensor  23  measures the detected angular velocity w (motor angular velocity measurement step S 3 ), calculates the difference between the detected angular velocity ω and the target angular velocity ω*, and confirms whether the deviation angular velocity Δω is higher than the angular velocity threshold Δω1 (deviation angular velocity confirmation step S 4 ). 
     Next, as shown in  FIG. 4D , when the rider pulls the handle  4  towards the rider side, the inverted two-wheel apparatus  1  tilts to the rider side. 
     Next, as shown in  FIG. 4E , the inverted control works to cause the inverted two-wheel apparatus  1  to travel while maintaining the inverted state. More specifically, the inverted two-wheel apparatus  1  travels towards the rider side in order to maintain the inverted state. 
     Next, as shown in  FIG. 4F , the inverted two-wheel apparatus  1  comes in contact with the foot of the rider, decreasing the travel speed of the inverted two-wheel apparatus  1 . This causes the detected angular velocity ω to deviate largely from the target angular velocity ω* from time T1 to time T2, as shown in  FIG. 5 . That is, the deviation angular velocity Δω increases. When the time reaches time T2, the deviation angular velocity Δω becomes equal to or higher than the angular velocity threshold Δω1 (deviation angular velocity confirmation step S 4 : NO). Then, the inverted control is once stopped and the stop control is started in order to stop the wheels  21  (wheel stop step S 41 ). As a result, the inverted two-wheel apparatus  1  does not travel towards the rider side but stops while staying in contact with the foot of the rider, as shown in  FIG. 4G . 
     Next, when both load sensors  33 L and  33 R detect the load, the completion of the step-on-platform action is detected (step-on-platform completion detection step S 5 ). The steps, from the motor angular velocity measurement step S 3  to the deviation angular velocity confirmation step S 4  or to the wheel stop step S 41 , are repeated until the completion of step-on-platform is detected. More particularly, when the completion of the step-on-platform action is detected, the inverted control is restarted (inverted control restart step S 6 ). Note that the step-on-platform completion detection step S 5  of this control method may also be executed by the step-on-platform completion detection unit  57 . More specifically, based on the load information indicating that the load is placed on both the step  31 L and the  31 R, the step-on-platform completion detection unit  57  may determine that the rider has completed the step-on-platform action. In addition, at least the deviation angular velocity confirmation step S 4  may be performed by the feedback compensation control unit  53 . In this case, the feedback compensation control unit  53  may be executed from the time the start of the rider&#39;s step-on-platform action is detected to the time the completion of the rider&#39;s step-on-platform action is detected. 
     Finally, when it is detected that the rider has stepped off the platform (step-off-platform detection step S 7 ), the control of the inverted two-wheel apparatus  1  is completed. More particularly, it is determined that the rider has stepped off the platform, for example, when the load on the load sensors  33 L and  33 R becomes smaller than a predetermined value or the load is not detected. 
     As described above, the inverted control can be performed in the first embodiment to allow the inverted two-wheel apparatus  1  to travel while maintaining the inverted state. The stop control can also be performed in the first embodiment based on the magnitude of the deviation angular velocity Δω to inhibit the inverted two-wheel apparatus  1  from keeping on pushing the foot of the rider when the rider steps on the platform. In addition, the load sensors  33 L and  33 R can detect the start and the completion of the rider&#39;s step-on-platform action, suitably performing the stop control of the inverted two-wheel apparatus  1 . 
     Second Embodiment 
     Next, an inverted two-wheel apparatus in a second embodiment is described with reference to  FIG. 6 . The inverted two-wheel apparatus in the second embodiment is similar to the inverted two-wheel apparatus in the first embodiment except that a torque sensor is provided. The other components of the configuration are the same as those of the configuration in the first embodiment and therefore the same reference numbers are used for the corresponding components. 
     As shown in  FIG. 6 , an inverted two-wheel apparatus  201  includes a torque sensor  24 . The torque sensor  24  detects the detected torque T of the wheels  21 . The torque sensor  24  may calculate the detected torque T from the electric current supplied to the motor  22 . The torque sensor  24  outputs the detected torque T to a feedback compensation control unit  253 . 
     The feedback compensation control unit  253  includes a determination unit  255 . The determination unit  255  calculates the torque derivative DT by differentiating the detected torque T. In addition, the determination unit  255  determines whether the calculated torque derivative DT is equal to or higher than the torque derivative threshold DT1. The torque derivative threshold DT1 is stored in advance in the determination unit  255 . The feedback compensation control unit  253  receives the signals about the deviation angular velocity Δω and the deviation attitude angle Δη. The feedback compensation control unit  253  outputs the signal about the target torque T*. 
     If the torque derivative DT is lower than the torque derivative threshold DT1, the feedback compensation control unit  253  outputs the inverted control torque Tt* as the target torque T*. The inverted control torque Tt* is a torque value for allowing the inverted two-wheel apparatus  1  to travel based on the load information m while maintaining the inverted state. 
     On the other hand, if the torque derivative DT is equal to or higher than the torque derivative threshold DT1, the feedback compensation control unit  253  outputs the stop torque Ts* as the target torque T*. 
     Second Control Method 
     Next, the second control method in the second embodiment is described with reference to  FIG. 4 ,  FIG. 5 , and  FIG. 7 . For the same steps as those in the control method in the first embodiment (see  FIG. 3 ), the same reference numerals are used. 
     As in the control method in the first embodiment described above, the step-on-platform action start detection step S 1  and the inverted control step S 2  are performed. After that, the motor rotation angle sensor  23  measures the detected torque T (torque measurement step S 3 ), and the determination unit  255  calculates the detected torque derivative DT from the detected torque T and confirms whether the detected torque derivative DT is higher than the torque derivative threshold (detected torque derivative confirmation step S 4 ). 
     Next, as shown in  FIG. 4D , when the rider pulls the handle  4  towards the rider side, the inverted two-wheel apparatus  201  tilts to the rider side. 
     Next, as shown in  FIG. 4E , the inverted control works to cause the inverted two-wheel apparatus  201  to travel towards the rider side while maintaining the inverted state. 
     Next, as shown in  FIG. 4F , the inverted two-wheel apparatus  201  comes in contact with the foot of the rider, decreasing the travel speed of the inverted two-wheel apparatus  201 . This causes the detected angular velocity ω to deviate largely from the target angular velocity ω* as shown in  FIG. 5 . That is, the deviation angular velocity Aw increases. When the deviation angular velocity Aw increases, the feedback compensation control unit  253  outputs a large torque value to the motor driver  54  as the target torque T* (inverted control torque Tt*) in order to travel while maintaining the inverted state. The detected torque T increases significantly with the result that the detected torque derivative DT exceeds the threshold DT1 (detected torque derivative confirmation step S 24 : NO). Then, the inverted control is once stopped and the signal about the stop torque Ts* is output to stop the wheels  21  (wheel stop step S 241 ). As a result, the inverted two-wheel apparatus  201  does not travel towards the rider side but stops while staying in contact with the foot of the rider, as shown in  FIG. 4G . 
     After that, as in the control method in the first embodiment, the step-on-platform completion detection step S 5  to the step-off-platform detection step S 7  are performed and the control of the inverted two-wheel apparatus  201  is completed. At least the deviation angular velocity confirmation step S 24  may be performed by the feedback compensation control unit  253 . In this case, the feedback compensation control unit  253  may be executed from the time the start of the rider&#39;s step-on-platform action is detected to the time the completion of rider&#39;s step-on-platform action is detected. 
     According to the second embodiment, the inverted control can be performed to allow the inverted two-wheel apparatus  201  to travel while maintaining the inverted state. The stop control can also be performed based on the detected torque derivative DT to inhibit the inverted two-wheel apparatus  201  from keeping on pushing the foot of the rider when the rider steps on the platform.