This chapter presents a comparative study of the topographical structure of three common biological robotic inspirations: human, canine, and feline feet. It is shown that the metrological roughness of each of the examined feet is customized for the specific locomotion demands of the species. The textural parameters manifest close correlation to the pressure distribution experienced in movement and gait. This correlation enhances the durability and structural integrity of the bio-analogue. It is also shown that the metrological function of the human (plantigrade) feet pads combine that of the back and the front feet pads of the digitigrade mammals examined. It is argued that integrating the targeted engineering of roughness within the design process of robotic feet can enhance the function of walking robots. Further, it offers elegant solutions to some of the current problems encountered in design of humanoids and other bio-inspired walking robots.
TopIntroduction
Autonomous robotic systems comprise two main groups. The first is termed as manipulation robotics, whereas the second is referred to as mobile robotics. Mobile robotics are conventionally categorized in terms of their locomotion configuration. The first group is referred to as wheeled, legged, or crawling machines. Each of these locomotion configurations offer certain advantages that renders the particular robot class suitable for special applications. Each of the robotic classes have limitations as well. One limitation faced by wheeled and crawling robots is mobility in natural terrains. This disadvantage, however, is offset in legged robots.
Legged robots offer superior mobility and they allow traversing difficult and inaccessible terrains. This is because their mode of locomotion, which uses legs, is advantageous in irregular terrains. Through varying the configuration of the legs, legged robots can selectively establish contact with the ground and adapt to surface irregularities. Legs also offer advantages in soft terrains (e.g. sand). The ability of selectively contacting the ground reflects positively on the energy consumption of the machine, improves stability, and widens the scope of applications. It is no surprise, therefore, that successful construction of legged robots have revolutionized application and utilization of robots in general.
Legged robots often mimic a biological model. Humanoids (which are biped machines) for example, mimic human locomotion (Hirai et al., 1998; Kaneko et al., 2008; Park et al., 2005; Radford et al., 2015; Kojima et al., 2015). Other machines are inspired by dinosaurs (Fukuoka and Akama, 2014), apes (Leong and Johnston, 2016), dogs (Tan et al., n.d; Sheba et al., 2018; Hunt, Szczecinski, and Quinn, 2017; He et al., 2019), cats (Kwon et al., 2015; Hayashi, Kato and Chobonyan, 2015; Liu et al., 2017; Dupeyroux et al., 2017), insects (Koh et al., 2015; Szczecinski et al., 2015; Cardinaels et al., 2017), and reptiles (Gao et al., 2014; Yu et al., 2018; Luo et al., 2014; Vespignani et al., 2015; Tanaka and Tanaka, 2015; Liu et al., 2016), among other analogs. The field is growing rapidly and many biological examples are being studied for inspiration.
Mammalian locomotion stances may be classified in terms of the part of the foot engaging the ground while moving. Accordingly, three locomotion styles are typically mentioned in literature. The first is sole walking, termed as plantigrade, as that practiced by humans, bears and some species of apes. The second is the so-called digitigrade, which stands for toe walking (practiced by quadrupeds such as cats and dogs). The third class of locomotion is known as unguligrade, which denotes walking on nails or hoofs as in the case of horses and cattle.