History of Robotics Research and Development of Japan2001BusinessOmni-directional Power Assisted Cart

S. Fujiwara	Panasonic Corporation
H. Kitano	Panasonic Corporation
H. Yamashita	Panasonic Corporation
H. Maeda	Panasonic Corporation
H. Fukunaga	Panasonic Corporation

In this research, we pay attention to the power assisted technology as substitution of human operating force and I present one of its application. The purpose of this research is developing an omni-directional cart with power assist system which can carry a heavy load about 600 kgf, which does not make it conscious of existence of a motor, but can be operated as easily as a shopping cart in a supermarket. First of all, I describe the force sensors. The handle detects the operator’s force and feeds it back to the driving wheels, which allows an inexperienced operator to operate the cart easily. However, if the value of detected force goes out of range, there is a possibility that the heavy cart goes out of control, which is extremely dangerous. I devised a force sensing system less sensitive to variations of the environment and needing less displacement to detect the operating force. The system consists of an eddy current type of three gap sensors and a leaf spring structure, which allows control to be detected in relation to two translation axes and one rotation axis corresponding to omnidirectional locomotion. To realize the driving part, we place the universal wheels at the 4 corners of the cart, these wheels are powered by 4 motors which are driven by speed control calculated from operator’s force. Due to the relatively long body of the cart, it was difficult to keep the balance between lateral movement and turning movement of the cart when shifting the cart laterally. Therefore we modified the equation for calculating the cart turning speed so that the moment, which was driven by the operating force in the right/left direction, was offset. This way, we could stabilize the balance, resulting in a largely increased operating performance in the lateral direction. As an operator pushing the cart cannot see persons or obstacles forward because the car is too big, usually, an operator pulls a cart single hand. But during the one-hand pull-operation, the cart tended to run off its course to the right/left, especially during cornering. From this fact, the control system can make the difference between operation with one or both hands for gripping and applies 2-DOF driving (forward and backward, and turning) to one hand operation or 3-DOF driving (forward and backward, left and right, and turning) for control of the holonomic ODV. And I describe the function to restrict acceleration, measures to reduce vibration during universal wheel driving and ways to improve universal wheel durability. 6th (2001) Technical Innovations Awards

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