Kinematic analysis and prototyping of ACROBAT omnidirectional mobile mechanism in a single layer ball transmission

Abstract

In this paper, we present motion analysis and prototype design of a new omni-directional wheel mechanism "ACROBAT-S". The authors group has proposed a special kind of transmission with a dual-ball configuration for transmit drive powers to wheel shaft and steering shaft of an active-caster mechanism (ACROBAT). In the transmission design, two balls are required where one ball is used for combining the two motor powers to rotate the ball in 2D way while another ball is for distributing the combined power to the wheel and steering. The transmission design enables an omnidirectional robot with three active casters for controls 3D motion of a robot by three motors with no redundancy. To reduce the number of friction drive between balls and rollers in the first design, a new type of ACROBAT with a single ball transmission (ACROBAT-S) is proposed in this paper. The proposed new design with single ball configuration contributes to reduce the number of friction drives between balls and rollers for enhancing an energy efficiency and accuracy of robot movement. To design a proposed mechanism, a kinematics of a ball, a roller and active-caster motions are analyzed to derive a mechanical condition for the prototype design. In this paper, we design and build a prototype of a single wheel and conduct experiments. From the results, it was confirmed that an expected motion can be realized.

Human-powered vehicle capable of movement in the longitudinal and lateral directions

“…Based on the same principle as that of the omni wheel, some omnidirectional wheel mechanisms have been developed, such as the Swedish wheel that has outer rollers arranged obliquely (Erland, 1974), an active omni wheel whose main body and outer rollers are both actively driven by using a differential gear mechanism (Komori et al, 2016), and an omnidirectional wheel with dual rings that are combined as a sphere driven by helical gears (Fujimoto et al, 2018). Another example that uses principles different from these mechanisms have also been developed: an omnidirectional vehicle in which the relative positions of the three wheels are variable (Terakawa et al, 2018), an omnidirectional vehicle that has caster type wheels with an offset between the steering axis and the ground contact point (Campion et al, 1996), and other various types of omnidirectional vehicles (Pin and Killough, 1994;West and Asada, 1995;Wada and Mori, 1997;Isoda et al, 1999;Yamashita et al, 2003;El-Shenawy et al, 2006;Mourioux et al, 2006;Tadakuma et al, 2008;Kumagai and Ochiai, 2008;Ren and Ma, 2015;Maeda and Ando, 2015;Masuda et al, 2017;Kato and Wada, 2018).…”