Toyota Motor Corp released "Winglet," a new personal transport assistance robot that users ride in a standing position, Aug 1, 2008 (See related article). For its drive mechanism, the robot employs an in-wheel motor combined with a planetary reduction gear.
The robot only has two wheels and maintains an upright posture using a control similar to the mechanism of an inverted pendulum, which always stands upright. An inverted pendulum is like a broom balanced on the palm that is moved back and forth in order to keep the broom standing.
In fact, the motors for the right and left wheels rotate forward or backward so that the robot is constantly under control to avoid stumbling. The in-wheel motors, each of which is composed of a brushless DC motor and a planetary reduction gear, are located on both sides. The company has not unveiled the motor output, the reduction ratio and the capacity of the Li-ion rechargeable battery serving as the power source.
In order to make the robot go forward, the rider shifts his or her weight to the front, just like tilting a pendulum. But if the rider keeps leaning, the robot eventually falls forward. Thus, the motors are rotated to move the robot forward so that its posture can be maintained.
On the other hand, the rider puts his/her weight on the back side to halt the robot. This reduces the torque of the motor and stops the robot without using a friction brake.
The robot turns basically by detecting shifts in the rider's weight. When the bar protruding in the center, which serves as a steering control, is moved to the right or left, the angle sensor detects the rider's intention to turn. Then, the robot makes a turn by varying the speeds of the right and left wheels.
If the rider puts his/her weight only on one foot, the bar itself tilts to make the robot turn. The L type, which comes with a steering control, has a slide switch on its upper left portion. The rider can also make the robot turn by operating the switch.
The tread of the latest robot is 360mm long and its step height is 165mm. With this layout, a control unit, gyro, angle sensors and a Li-ion rechargeable battery are arranged between both feet, with the rechargeable battery placed on top of the other components. The travel distance of the S type is limited to 5km as the capacity of the battery used is smaller than those of the other types.
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