Abstract:
A wheeled moving robot including a main body; wheels provided at least at opposite sides of the main body and configured to move the main body; an actuator configured to generate torque which rotates the wheels; a detector configured to detect whether the main body moves when the wheels rotates by the actuator; and a compensation unit configured to perform an auxiliary movement which pushes an auxiliary wheel in front or rear of the main body toward a floor based as a detection result of the detector.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-317615, filed on Oct. 31, 2005; the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wheeled moving robot.  
         [0004]     2. Description of the Related Art  
         [0005]     A wheeled moving robot which drives wheels and moves freely in an operational environment may not be able to start to move from a still state when there are bumps on the floor surface and/or the static friction force between the wheels and the floor surface is large.  
         [0006]     In fact, the static friction force between the wheels and the floor surface changes considerably in relation to the materials of the wheel rims and the materials of the floor surface. In order that the robot can move regardless of the materials, the robot must have a large sized actuator which generates large torque at a movement start and therefore has high electricity power consumption. However, since the wheeled moving robot is mainly driven by a battery, a small sized robot which has low electricity power consumption is desirable.  
         [0007]     Moreover, as a method of compensating the static friction force of the actuator, there is proposed a method that compensates the static friction of a shaft at a rotation start by adding dither compensation torque instructions to the actuator so as to prevent a delay of the rotation start. (See, Japanese patent application (KOKAI) 8-286759) However, this method merely enhances a response performance of the actuator at the rotation start of the shaft insofar as the actuator can generate sufficient torque which exceeds the static friction force, such as with an industrial robot. However, the proposed method can not rotate the shaft when the torque generated by the actuator can not exceed the static friction force.  
       SUMMARY OF THE INVENTION  
       [0008]     According to one aspect of the present invention, there is provided a wheeled moving robot apparatus which includes a main body; wheels provided at least at both sides of the main body and configured to move the main body; an actuator configured to generate torque which rotates the wheels; a detector configured to detect whether the main body moves when the wheels are rotated by the actuator; and a compensation unit configured to perform a auxiliary movement which pushes an auxiliary wheel in front or rear of the main body towards a floor according to a detection result of the detector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a block diagram of the wheeled moving robot;  
         [0011]      FIG. 2  is a side view showing a moving unit of the wheeled moving robot;  
         [0012]      FIG. 3  is a top view showing a moving unit of the wheeled moving robot;  
         [0013]      FIG. 4  is a block diagram of the push-pull type solenoid;  
         [0014]      FIG. 5  is a graph showing a relation between the speed of the wheeled moving robot and the frictional force of the floor surface;  
         [0015]      FIG. 6  is a side view showing a relation between the setting angle θ of the auxiliary wheel and the push force Fsn against the floor surface;  
         [0016]      FIG. 7  is a block diagram showing functions of the wheeled moving robot;  
         [0017]      FIG. 8  is a flowchart showing a movement of the wheeled moving robot; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  is a block diagram of a wheeled moving robot according to an exemplary embodiment of the present invention. The wheeled moving robot includes a robot main body  1  having a battery, a controller, a speed sensor (not shown), a interface unit  2  installed the robot main body  1  having a liquid crystal display, a camera, a speech synthesizer, and a speech recognizer (not shown), and a moving unit  3  which freely moves the robot main body  1 .  
         [0019]     Next, the structure of the moving unit  3  is described in relation to  FIGS. 2 and 3 . As shown in  FIG. 3 , moving wheels  32  are mounted in parallel at both sides (upper and lower parts in  FIG. 3 ) of a moving base  31 .  
         [0020]     Each moving wheel  32  is driven by an actuator  33  to which the movement wheel  32  is mounted. Moreover, each actuator  33  is provided with an encoder  34  which measures a rotation and a rotational speed of the moving wheel  32 . Furthermore, as shown in  FIG. 2 , an auxiliary torque unit  4 , which assists a driving torque for moving the wheeled moving robot, has auxiliary wheels  35  mounted front and rear of the robot main body  1 , and push-pull type solenoids  37  which push the auxiliary wheels  35  against the floor surface. The moving base  31  is attached to the auxiliary wheel  35  and the push-pull type solenoid  37  at a setting angle θ through a support unit  36 , respectively. Since each of the auxiliary torque units  4  is mounted front and rear of the moving wheels  32 , the auxiliary torque units  4  also play a role which supports the robot main body  1  with the moving wheels  32  so that the wheeled moving robot can maintain a stable posture. In addition, each moving wheel  32  may be driven by an actuator  33 .  
         [0021]     Next, the above push-pull type solenoid  37  is described in detail referring to  FIG. 4 . The push-pull type solenoid  37  has a base  371  which connects with the support unit  36 , and a socket  372  which fits with a shaft  373  (what is extended from the support unit  36 ) and is mounted in the center of the base  371 . Moreover, a plunger  374  is mounted with the shaft  373  on the opposite end of the base  371 . The plunger  374  is connected to the auxiliary wheel  35 , pushes the auxiliary wheel  35  toward the floor surface (lower direction in  FIG. 4 ) by a push force Fsn when a coil  375  mounted with the base  371  around the shaft  373  is excited, and pulls back the auxiliary wheel  35  toward the opposite side of the floor surface (upper direction in  FIG. 4 ) when the coil  375  is unexcited.  
         [0022]     Here, the relation between the frictional force and torque generated by the actuator  33  is explained in regard to the situation where the stopped wheeled moving robot cannot move. In order to keep the explanation simple, in this embodiment, the friction coefficient is defined as the rolling-friction coefficient converted between the moving wheel  32  and the floor surface, and includes a coefficient of dynamic friction μ m  and a coefficient of static friction μ s . In addition, the coefficient of dynamic friction μ m  is proportional to speed.  
         [0023]      FIG. 5  shows a relation between a speed V of the wheeled moving robot and the frictional force between the moving wheel  32  and the floor surface. A horizontal axis shows the speed V of the robot main body  1 , and a vertical axis shows the frictional force F(scalar) acting on the moving wheels  32  in a direction opposite to the moving direction. Moreover, a broken line shows a driving force of the moving direction converted to a maximum torque τ max  which the actuator  33  can generate.  
         [0024]     A maximum static friction force Fs acts on the moving wheel  32  until the wheeled moving robot begins to move (in  FIG. 5 , V=0). The maximum static friction force Fs is determined by the static friction coefficient μ s  and a mass W of the wheeled moving robot, and is shown the following equation. 
 
 Fs=μ   s   ·Wg    (1), 
 
 where g is gravitational acceleration. 
 
         [0025]     The friction force becomes a small value when the wheeled moving robot begins to move, and when the speed V of the wheeled moving robot reaches a speed Δ V, it changes from the static friction force to the dynamic friction force.  
         [0026]     A torque τ required to initiate rotation of the moving wheels  32  by exceeding the maximum static friction force Fs is shown by the following equation, since two of the moving wheels  32  are mounted with the moving base  31 : 
 
τ= Fs·r/ 2=μ s   ·Wg·r/ 2   (2), 
 
 where r is a radius of the moving wheel  32 . 
 
         [0027]     If the maximum torque τ max  is smaller than the torque τ required to initiate rotation of the moving wheels  32 , the moving wheels  32  do not rotate. In this case, the maximum torque τmax is shown the following equation: 
 
 τ=μ   s   ·Wg·r/ 2&gt;τ max    (3), 
 
         [0028]     The generated torque of the actuator  33  is insufficient by an amount ((μ s ·Wg·r/2)−τ max ).  
         [0029]     Usually, since the coefficient of static friction μs is dozens times or more than coefficient of dynamic friction μ m , the maximum static friction force Fs is very large as compared with the dynamic friction force. Therefore, the actuator  33  is enlarged if an insufficient torque amount is compensated for by means of the actuator  33 .  
         [0030]     So, in this embodiment, to compensate for the insufficient torque amount ((μ s ·Wg·r/2)−τ max ), each the push-pull type solenoid  37  pushes the auxiliary wheel  35  against the floor surface by the push force Fsn.  
         [0031]     Next described are the push force Fsn required so that the auxiliary wheels  35  and the push-pull type solenoids  37  work as the auxiliary torque unit  4 , and the setting angle θ, referring to  FIG. 6 . The rear auxiliary torque unit  4  works when the wheeled moving robot moves toward a front direction and the front auxiliary torque unit  4  works when the wheeled moving robot moves toward a rear direction.  
         [0032]     When the wheeled moving robot moves toward a front direction, the push-pull type solenoid  37  of the rear side pushes the auxiliary wheel  35  of the rear side against the floor surface in a direction opposite to the moving direction by push force Fsn. At this point, a parallel component of the push force Fsn to the floor surface is Fsn·cos θ. The force Fsn·cos θ acts on the wheeled moving robot toward the moving direction as a reaction against the parallel component of the push force to the floor surface.  
         [0033]     In order that the push-pull type solenoid  37  of the rear side compensates for the insufficient torque amount ((μ s ·Wg·r/2)−τmax), the force of the moving direction acting on the wheeled moving robot needs to exceed the insufficient torque amount ((μ s ·Wg·r/2)−τ max ).  
         [0034]     That is, if the following inequality is met, the wheeled moving robot can move even if the generated torque of the actuator  33  is insufficient. 
 
 Fsn· cos θ≧(μ s   ·Wg·r/ 2)−τ max    (4) 
 
         [0035]     The above mentioned equation (4) varies with the maximum torque of the actuator  33 , the friction coefficients between the floor surface and the moving wheel  32 , and the mass of the wheeled moving robot. Therefore, the push force Fsn and the setting angle θ are determined so as to fill the above mentioned equation in consideration of components of the wheeled moving robot and the environments in which the wheeled moving robot is used.  
         [0036]     Next, a motion control when moving a wheeled moving robot is explained in relation to  FIG. 7 , which is a block diagram showing functions of the wheeled moving robot. The robot main body  1  has a controller  5  in its interior. The controller  5  is coupled to the actuator  33  and the encoder  34  of each moving unit  3 , and generates a moving-target control command to control the torque of the actuator  33 . Furthermore, the controller  5  is coupled to the auxiliary torque unit  4 , and generates a compensation torque control command based on information measured for the encoder  34 , and controls the auxiliary torque unit  4 .  
         [0037]     Next, the motion control when moving the wheeled moving robot is described referring to the flow chart of  FIG. 8 .  
         [0038]     First, according to the moving-target control command which the controller  5  in the robot main body  1  generates, the actuator  33  generates a driving torque and rotates the moving wheel  32  (Step S 101 ). Next, the controller  5  decides whether the robot main body  1  begin to move based on the rotation and the rotation speed of the moving wheel  32  which the encoder  34  measures (Step S 102 ). The motion control ends if the robot main body  1  begins to move.  
         [0039]     If it is determined in Step S 102  that the robot main body  1  does not begin to move, the controller  5  signals the actuator  33  to generate an increased torque (Step S 103 ), and the controller decides whether the increased torque exceeds the maximum torque (Step S 104 ). When the torque of the actuator  33  does not exceed the maximum torque as determined in Step S 104 , the controller  5  returns to the Step S 101  in order to rotate the moving wheel  32  with the increased torque.  
         [0040]     On the other hand, when the torque of the actuator  33  exceeds the maximum torque by the decision of the Step S 104 , controller  5  decides that the maximum static friction force Fsn is larger than the maximum torque of the actuator  33 , or that the wheeled moving robot can not begin to move due to a bump in the floor surface, and generates a compensation torque control command to the push-pull type solenoid  37  of the rear side. Thereby, the push-pull type solenoid  37  pushes the auxiliary wheel  35  against the floor surface (Step S 105 ). At this time, the actuator  33  generates the maximum torque.  
         [0041]     After pushing of the auxiliary wheel  35 , the controller  5  generates a further compensation torque control command to the push-pull type solenoid  37  so that the push-pull type solenoid  37  pulls back, and the auxiliary wheel  35  returns to the position before pushing (Step S 106 ). Next, the controller  5  decides whether the pushing action of Step S 105  resulted in the robot main body  1  beginning to move (Step S 107 ), and ends motion control if the robot main body  1  begins to move.  
         [0042]     On the other hand, if the robot main body  1  does not begin to move as determined in Step S 107 , after checking the number of times of retrying the Step S 105 -Step S 107 , in a Step S 108 , when fewer than a predetermined number of retry times, the controller  5  returns to Step S 105  and generates the compensation torque control command to the push-pull type solenoid  37 , so that the push-pull type solenoid  37  pushes and pulls the auxiliary wheel  35 . Thereby, the controller  5  retries motion control by pushing the auxiliary wheel  35  of the push-pull type solenoid  37  and the maximum torque of the actuator  33 . The auxiliary motion controls (from the step S 105  to the step S 107 ) are retried only a predetermined number of times (N times). This is because a contact state between the floor surface and the auxiliary wheel  35  changes delicately by pushing the auxiliary wheel  35  in the Step S 105  and the maximum static friction force Fs may change significantly.  
         [0043]     In addition, when the controller  5  decides that the auxiliary motion controls have been retried N times or more in the Step S 108 , the controller  5  decides that the wheeled moving robot can not be moved by the actuator  33  and the push-pull type solenoid  37  and completes the motion controls by generating an error. When the number of times of retrying is less than N times, the controller  5  returns to the Step S 105  and repeats the same motion controls.  
         [0044]     In addition, the controller  5  can decide by the above mentioned encoder  34  and by using a speed sensor and an acceleration sensor in the robot main body  1  whether the robot main body  1  begins to move at the Step S 102  and the Step S 107 . By using the speed sensor and the acceleration sensor, an error of deciding a motion start can be reduced when the moving wheel  32  idles at the bump.  
         [0045]     Thus, according to this embodiment, when the wheeled moving robot can not begin to move even with the maximum torque of an actuator  33  being applied because of the influence of the static friction force or a bump in the floor surface, the wheeled moving robot can be forced to move without enlarging the actuator  33  by means of the auxiliary torque unit  4  by pushing the push-pull type solenoid  37  and pushing the auxiliary wheel  35  against the floor surface, so that the wheeled moving robot can be miniaturized. Moreover, a small wheeled moving robot which does not have unnecessary components can be realized by using the auxiliary wheel  35  not only as stable support of the robot main body  1  but as a part of the auxiliary torque unit  4 . Furthermore, energy consumption of the wheeled moving robot can be reduced by exciting the push-pull type solenoid  37  only when pushing the auxiliary wheel  35  against the floor surface at beginning movement, and otherwise maintaining solenoid  37  unexcited when the wheeled moving robot stops and moves.  
         [0046]     In addition, the present invention is not limited to the above mentioned embodiment and can be implemented by transforming components in ranges which do not deviate from the summary at an operation stage. Moreover, various inventions can be formed with proper combinations of various components employed in the above mentioned embodiment. For example, one or more components may be omitted from the components above described.  
         [0047]     Accordingly, it should be understood that numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.