Mechanical Design of Step-Climbing Vehicle with Passive Linkages

In recent years, mobile robots are expected to perform various tasks in general environments such as nuclear power plants, large factories, welfare care facilities and hospitals. However there are narrow spaces with vertical gaps made by two horizontal floors in such environments and it is difficult for general car-like vehicles to run around there. Generally, the mobile robots are required to have quick and efficient mobile function for effective task execution. The omni-directional mobility is useful for the tasks, especially in narrow spaces, because there is no holonomic constraint on its motion (Campion et al., 1996; Bicchi et al., 2003). Furthermore, the step overcoming function is necessary when the vehicle passes over the vertical gaps. Thus, in order to run around general environment, the vehicle needs to equip both of two functions. In related works, various types of omni-directional mobile systems are proposed (legged robots, ball-shaped wheel robots, crawler robots, and so on). The legged robot (Hardarson, 1997; Endo & Hirose, 1999) can move in all directions and passes over rough terrain. However, its energy efficiency is not so good because the mechanisms tend to be complicated and the robot needs to use its actuators in order to only maintain its posture. The robot with ball-shaped wheels can run in all directions (Wada & Asada, 1999), however, it cannot run on the rough grounds. The special crawler mechanism (Damoto & Hirose, 2002) is also proposed for the omni-directional mobile robot, however, which can climb over only small steps. Therefore, there is still a lack of well-adapted mobile system for both narrow spaces and step climbing operation. Therefore, we are developing a holonomic omni-directional vehicle with step-climbing ability. (Chugo et al., 2005) Our prototype has seven special wheels with actuators (Fig. 1) and a passive suspension system (Asama et al., 1995). (Fig. 2) The special wheel consists of twelve cylindrical free rollers and helps to generate omni-directional motion with suitable wheel arrangement and wheel control. The passive linkage mechanism ensures that the vehicle can pass over the step smoothly when the wheel contacts the step, changing the body configuration of the vehicle. No sensors and no additional actuators are required to pass over the non-flat ground. O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m