Improved Design and Analysis of the Flexible Screw Mechanism for a Worm Robot

In the previous study, we proposed a new type of flexible screw mechanism using a roller to decrease the friction. And the pipe-in robot with this mechanism can complete curved shapes motion was tested. However, this mechanism generates large lateral deflection during curved shape movement which cause low drive efficiency. By modifying the drive shaft of this mechanism, it can complete curved shapes motion with less lateral deflection than the single spring shaft. In this paper, we analyzed and tested the improved design of the shaft compared with the single spring shaft. From the experimental results, the lateral deflection of the shaft is reduced and the transmission efficiency is enhanced. Published by CSP © 2019 the Authors 481 2. Analytical model of the shaft In our previous study[14] of the FSM mechanism, the front body and the rear use the compression spring to rotate and move alternately. In order to analyze the robot with FSM work in curved pipe, we modeled the shaft of the FSM in an experiment platform and it is simplified as follows: • In using the Euler-Bernoulli beam model, the spring can be equivalent to an equivalent beam model [15],when performing bending . • While the length of the spring meet the slender beam theory, the deformation of the axis of the spring is analyzed in plane-coordinate system. • Since the bending stiffness of the drive shaft is smaller than the compression stiffness in actual work, we dicussed the deformation calculated by bending force. Figure 1. The model of the spring in experimental platform As shown in fig. 1, the spring was analyzed in the two-dimensional plane where the spring get the maxium lateral displacement. F1x, F2x denote the drive force and F1y, F2y denote the support force. Point O, B is the end of the spring shaft.  OB is the axis of the spring. Point A is the symmetry point of  OB , and α is the angle between the plane which two fixed ends perpendicular to. The formula was established as follow.

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