Abstract
Stairs are common obstacles in indoor environments and are difficult to overcome for robots. The speed of robot stair-climbing should be similar to that of humans for commercial products, but their speed remains limited. Additionally, the variety of dimensions of stairs is also a significant problem for robust stair-climbing by robots. In this paper, a curved spoke-based tri-wheel mechanism is proposed for fast and robust stair-climbing. The goal speed of stair-climbing is similar to the human speed for variously sized stairs. The proposed wheel system is composed of a tri-wheel mechanism with a curved spoke, wherein the dimensions of the mechanism are determined based on a kinematic analysis. Between the tri-wheels, a stopper mechanism acts to make the initial condition of the sequential stair-climbing the same as the initial starting condition. Static analysis to analyze the minimum friction coefficient is performed to verify the performance of the robot. Experiments based on the prototype are performed to verify the stair-climbing speed for variously sized stairs; the results indicate that fast and robust stair climbing performance is achieved. These findings can be used to design an indoor service robot for various applications.
Highlights
Stairs are common and difficult obstacles for robots in indoor environments
To design a high-performance robot, the center of gravity (CoG) should be coincident with the center of rotation (CoR) so as to guarantee a low required friction coefficient
The results show that the proposed robot required relatively little friction coefficient to perform stair-climbing
Summary
Stairs are common and difficult obstacles for robots in indoor environments. To create a working indoor service robot, stairclimbing capabilities are necessary. RHex [10], with curved legs developed for unstructured environments, has been used for stair climbing Modified wheel mechanisms, such as the tri-wheel, have been found to realize effective stair climbing [11]. Several studies have focused on these systems; the systems involve several drawbacks, such as friction problems because of edge contact (tracked), complicated design (wheel-linkage), the need for a high degree-of-freedom (DOF) (wheellinkage and curved wheel), and poor adaptation to different stair sizes (modified wheel) With low minimum coefficient of friction, the robot has large stability margin and the robot can climb relatively rough surface Based on these analyses, the design parameters can be determined optimally.
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