Active omni wheel capable of active motion in arbitrary direction and omnidirectional vehicle

Abstract

A transportation vehicle or mobile robot that can move to a target location in an arbitrary direction on the floor is important to ensure that work can proceed quickly and effectively in a limited space. To move in an arbitrary direction, conventional methods such as omni wheels have free rollers along the outer circumference of the wheel that can rotate passively. However, the conventional methods are difficult to control precisely because of the rotational resistance of the free rollers. In addition, the direction that the conventional methods can move actively by themselves is limited. This paper proposes a novel mechanism called the active omni wheel, which is able to actively move in an arbitrary direction by using only one wheel unit. The active omni wheel is composed of a main body and outer rollers arranged around the outer circumference of the wheel. By using a differential gear mechanism, the active omni wheel enables active rotation of not only the main body of the wheel but also the outer rollers. The theoretical equation of motion of the active omni wheel is clarified to control the wheel. An omnidirectional vehicle using the active omni wheel is discussed. The appropriate arrangement of wheels that enables the omnidirectional vehicle to move actively in arbitrary directions by using the active omni wheel is shown and the motion theory is constructed. This paper also discusses the structure appropriate for the vehicle using the active omni wheel, including the arrangement of input shafts, the structure supporting the wheels, the main body of the vehicle, and its suspension. The active omni wheel and omnidirectional vehicle were designed and manufactured. Experiments conducted on the manufactured vehicle verify the effectiveness of the active omni wheel and the omnidirectional vehicle.

A Novel Omnidirectional Mobile Robot With Wheels Connected by Passive Sliding Joints

“…Here, , , and are constants. If the rotational velocity of the wheel and the relative velocity of the driving unit on the sliding joint are arbitrary, (7) and (8) give zero nonholonomic constraints for under the condition . This proves theoretically that SWOM can move at an arbitrary velocity with regard to three-DOF planar motion and can perform as an omnidirectional mobile robot.…”

“…First, we examine the translation without rotation of SWOM. If is given in (8) and the global and local reference frames are in agreement at the initial condition, the relative position of the driving unit on the sliding joint is given as follows: (12) where denotes the relative position of driving unit i on the sliding joint at the initial condition. When the movable range of the sliding joints is represented by , the reachable region of the main body of SWOM is obtained.…”

“…Their mobility allows applications such as a variable wheel arrangement mechanism [4], a highly efficient control method [5], and a competition robot with an omni-vision system [6]. The active omni wheel [8] enables both the main body of the wheel and the rollers to rotate actively. However, the omni wheel has disadvantages such as a low load capacity due to its complicated structure, unavoidable vertical vibration due to discontinuity of the ground contact point, and inability to surmount high bumps due to the small radius of the free rollers [9].…”

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

“…向移動機構は，位置と姿勢の 3 自由度を独立に制御することが可能であるため，非ホロノミックな移動機構に比 べ，複雑な経路設計が不要となる．また，人間が操縦する場合においても，狭所での移動を容易にする等，多く の利点がある．このため，このようなホロノミック全方向移動機構は，球形の車輪を複数輪用いるサッカーロボ ット(石田他， 2014)， や球形車輪１輪でバランス制御するロボット ， )， 全方向移動車イス ，あるいは全方向クローラを備えた車両 等にも広く 用いられている． ホロノミック全方向移動を実現する代表的な移動機構には，オムニホイール (Asama et al, 1995)やメカナムホイ ール といった車輪機構を利用したロボットシステムがあり歴史もながく広く利用されて いる．これらの機構は，自由回転する小さなローラを車輪に組み込むことで，車輪の横滑りを許容する構造とな っている．また，車輪の駆動に加えて小さなローラも独立に駆動することで全方向移動を行う車輪 (Komori et al, 2016)も提案されている．この車輪を複数用い，各車輪がそれぞれの方向へ速度を発生させるように取り付けるこ とで，全方向移動を実現する．これらの機構は，構造がシンプルで安価であるうえ，速度の制御が容易であるこ とから，室内環境で動作する移動ロボットには広く普及しているが，地面の凹凸の影響を受けやすく，段差踏破 性能が低い，振動が発生するという欠点があることから，屋外や実環境での利用には適さない． これらの問題を克服するため，筆者らが提案している全方向移動機構に「アクティブキャスタ」 is allowed to rotate about a vertical axis by a roller support Y-axis and a peripheral velocity prodused at a member which makes contact with a ball not on the large circle. Point on X-axis.…”

Experimental investigations of a highly maneuverable mobile omniwheel robot

“…One of the ways to ensure a high maneuverability of the robot is to use omniwheels, 12,13 which, when properly arranged, allow the robot to move in any direction without reorientation. Recently, many scientists have been engaged in developing various kinematic schemes of omniwheel robots and their control algorithms, 14,15 including spherical robots, when the platform with omniwheels is placed inside a spherical shell. 16,17 In spite of a large number and variety of publications devoted to omniwheel mobile robots, no experimental results have been presented to demonstrate their maneuverability.…”