Mobile Platform with Leg-Wheel Mechanism for Practical Use

Robots that can move over rough terrain with active body leveling are now in strong demand. Such a robot can have a variety of uses, such as carrying packages, assisting people who have difficulty in walking, and safety monitoring outdoors. Many robots capable of moving over rough terrain exist as research tools; however, few are suitable for practical use. These robots can be generally classified into the three categories. 1) Legged robots: These have excellent mobility with high stability. The mobility of legged robots has been extensively studied: for example, ASV (Song and Waldron 1989), the TITAN series (Hirose et al. 1985), DANTE II (Bares and Wettergreen 1997), the hexapod robot (Delcomyn and Nelson 2000), Tekken2 (Kimura et al. 2007), and Hyperion3 (Yoneda 2007). 2) Wheeled robots: These are most commonly selected for traversing continuous surfaces that include rough terrain. Because of their stability, maneuverability, and simple controls, wheels are the most frequently used mechanism for exploration rovers. Examples of wheeled mobile robots are Micro5 (Kubota et al. 2003), Rocky7 (Volpe et al. 1997), Shrimp (Siegwart et al. 2002), CRAB (Thueer et al. 2006), and Zaurus (Sato et al. 2007). These have passive linkage mechanisms. SpaceCat (Lauria et al. 1998) and Nanokhod (Winnendael et al. 1999) have active linkage mechanisms. The high-grip stair climber (Yoneda et al. 2009) is a crawler-type robot. 3) Leg-wheel robots: These attempt to combine the advantages of both legs and wheels in various configurations. Work Partner (Halme et al. 2003), Roller Walker (Endo and Hirose 2000), Zero Carrier (Yuan and Hirose 2004), Hylos (Grand et al. 2004), and PAW (J.A. Smith et al. 2006) are equipped with wheels placed at the ends of their legs; the Chariot series (Nakajima and Nakano 2008a,b, 2009a-c,Fig. 1), RoboTrac (Six and Kecskem’ethy 1999), and a wheel chair robot(Morales et al.2006) have separatewheels and legs;Whegs (Quinn et al. 2003; Daltorio et al. 2009) and Epi.q-1(Quaglia et al.2010) have four wheels composed of rotating legs or wheels; and Wheeleg (Lacagnina et al. 2003) has two front legs and two rear wheels. Although a legged robot is highly mobile on rough terrain, the mechanism is complex and more energy is required for walking. On the other hand, while wheeled robots are usually the best solution for continuous terrain, most cannot travel over discontinuous terrain. Generally speaking, a hybrid mechanism like Fig. 1 provides the strengths of both wheels and legs, although such mechanisms tend to be complex. Chariot 3 is equipped with four legs of three degrees of freedom and two independent wheels. On the other hand, Whegs is not complex, 7