**3.2. Air**

8 Will-be-set-by-IN-TECH

network also drives the control of the SMAs. The results have shown the system can reject disturbances thanks to the robustness of the nonlinear controller [55]. Each SMA wire drains

**Figure 3.** (a) Lamprey Robot with sonar array, (b) Lateral view of tail segment showing nitinol actuator,

*3.1.5. A biomimetic robotic jellyfish (Robojelly) actuated by shape memory alloy composite actuators* The newest and more advanced aquatic robot that uses SMA actuators is a jellyfish robot designed by [68]. The hydrogen-fuel-powered robot called "Robojelly" mimics the propulsion, morphology, kinematics and physical appearance of a medusa (jellyfish); the Aurelia aurita

The development of Robojelly has introduced a systematic method for the design and fabrication of SMA-based actuators called BISMAC (bio-inspired shape memory alloy composite). This method allows for bending the structure of the robot by means of SMA contraction [77]. Thanks to the BISMAC SMA arrangement, this robot was capable to mimic the physics and swimming characteristics of jellyfish in terms of A. aurita's bell geometry, passive relaxation mechanism, neutral buoyancy, frequency of motion, and

species. The bio-inspired actuators are made of silicone, SMA wires and spring steel.

Teflon vertebra and tensioning nuts and (c) Lateral view of pitch mechanism [81].

**Figure 2.** Micro biomimetic manta ray robot fish [79].

1.5*A* of electrical current when activated.

In aerial bio-inspired robots most of the applications are appendices. Here, we can identify two main categories: insects and birds. To the best of the authors' knowledge only one robotic flying insect has been developed, apart form the jumping robot described earlier. This can be explained by the flapping frequency needed, far form the SMA's capabilities, and also by their power requirements. For these reasons insect-like flying robots mostly adopt piezo-electric actuators. In fact, the flying insect prototype described below uses SMA to fold and unfold the wings, and not for the primary flapping motion. Despite SMA actuation speed does not allow the actuation of flapping wings, it could allow for other kind of wing actuation, such as morphing-wings.

### *3.2.1. Recent progress in developing a beetle-mimicking flapping-wing system*

In [51] a beetle-like insect robot inspired by the Allomyrina Dichotomapresents is presented. This robot features a morphing-wing airfoil capable of folding and unfolding the hind wing

#### 10 Will-be-set-by-IN-TECH 62 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

using SMA wires. A single small size DC motor drives the flapping mechanism. Figure 5 shows the prototype and the unfolding of the artificial flapping/morphing wing device.

Similar folding ratio of the robot's wings has been observed in comparison with the biological counterpart, accounting for 1.7 of value. On average, wing unfolding was completed within about 3*s* and the wing folded in about 4*s*.

**Figure 5.** Prototype of the robotic beetle and detail of the unfolding of the artificial wing [51].

### *3.2.2. BATMAV-a biologically inspired micro-air vehicle for flapping flight: artificial-muscle based actuation*

The BATMAV is a biologically inspired bat-like Micro-Aerial Vehicle (MAV) with flexible and foldable wings capable of flapping flight [2]. The robot features bat-inspired wings with a large number of flexible joints that allow mimicking the kinematics of a real bat flyer. Figure 6 details the overall structure of the robot, and the main connections of the SMA-like muscles.

BATMAV is the first robot that uses the SMA wires to play a dual role: first, as muscle-like actuators that provide the flapping and morphing wingbeat motions of the robot, and second, as super-elastic flexible hinges that join the wing's bone structure. Most of the experiments in [**?** ] were carried out with a two-degree of freedom wing capable of flapping at 3*Hz*. Despite the fact that their robot is able to achieve accurate bio-inspired trajectories, the results presented lack experimental evidence of aerodynamics measurements that might demonstrate the viability of their proposed design.

### **3.3. Ground**

Ground bio-inspired robots have been divided in two categories: the ones that uses actuated appendices (i.e, legged robots) and those that actuate the whole body, i.e. crawling robots such as snakes and worms.

62 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges SMA-Based Muscle-Like Actuation in Biologically Inspired Robots: A State of the Art Review <sup>11</sup> SMA-Based Muscle-Like Actuation in Biologically Inspired Robots: A State of the Art Review 63

**Figure 6.** BATMAV. Dual Role of Shape Memory Alloy wires: as actuation muscles, and super elastic joints. (Picture from https://sites.google.com/site/gheorghebunget/research/batmav, with permission).

## *3.3.1. Sensor fusion in a SMA-based hexapod bio-mimetic robot*

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using SMA wires. A single small size DC motor drives the flapping mechanism. Figure 5 shows the prototype and the unfolding of the artificial flapping/morphing wing device.

Similar folding ratio of the robot's wings has been observed in comparison with the biological counterpart, accounting for 1.7 of value. On average, wing unfolding was completed within

**Figure 5.** Prototype of the robotic beetle and detail of the unfolding of the artificial wing [51].

*3.2.2. BATMAV-a biologically inspired micro-air vehicle for flapping flight: artificial-muscle based*

The BATMAV is a biologically inspired bat-like Micro-Aerial Vehicle (MAV) with flexible and foldable wings capable of flapping flight [2]. The robot features bat-inspired wings with a large number of flexible joints that allow mimicking the kinematics of a real bat flyer. Figure 6 details the overall structure of the robot, and the main connections of the SMA-like muscles. BATMAV is the first robot that uses the SMA wires to play a dual role: first, as muscle-like actuators that provide the flapping and morphing wingbeat motions of the robot, and second, as super-elastic flexible hinges that join the wing's bone structure. Most of the experiments in [**?** ] were carried out with a two-degree of freedom wing capable of flapping at 3*Hz*. Despite the fact that their robot is able to achieve accurate bio-inspired trajectories, the results presented lack experimental evidence of aerodynamics measurements that might demonstrate

Ground bio-inspired robots have been divided in two categories: the ones that uses actuated appendices (i.e, legged robots) and those that actuate the whole body, i.e. crawling robots

about 3*s* and the wing folded in about 4*s*.

the viability of their proposed design.

such as snakes and worms.

*actuation*

**3.3. Ground**

In [44] SMABOT is presented, a hexapod biomimetic robot with two SMA actuators that allow for the motion of the two degree-of-freedom robot. Each SMA actuator produces 300*gram* − *f orce* of pull force. Figure 7 shows the SMABOT IV. SMABOT IV incorporates two-dimensional inertial navigation system for position control. The average speed when moving with tripod gait is 30*cm*/*min*. Its maximum power consumption is about 25*W* (the mass is 290*g*).

**Figure 7.** SMABOT IV, a SMA based hexapod robot with the IMU module, compass sensor and step touch sensors [44].

#### 12 Will-be-set-by-IN-TECH 64 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

#### *3.3.2. Omegabot: Crawling robot inspired by Ascotis Selenaria*

In [38] a robot inspired by the inchworm Ascotis Selenaria is presented. The robot, called Omegabot, is named after the omega (Ω) shape of the crawling motion of the inchworm. Figure 8 shows the Omegabot platform. Previous work about this robot can be also found in [37].

Experimental results report the first step for establishing an inchworm-like robot that can crawl on various terrains where conventional robots cannot move. The Omegabot uses a SMA coil actuator that requires a current of 200*mA* for activation. The frequency of motion is about 1*Hz*, limited by the response time of the SMA wires. The inchworm robot is manually controlled by an IR remote operation, and it achieves a maximum linear velocity of 5*mm*/*s*. The robot travels a distance of 5*mm* per stroke.

**Figure 8.** Omegabot, a biomimetic inchworm robot, grasps the branch of a wood, raises its head, and turns right. Bottom right: Proleg of Omegabot [38].

#### *3.3.3. An earthworm-like micro robot using shape memory alloy actuator*

In [34] a bio-mimetic micro earthworm-like robot with wireless control is proposed. The actuation mechanism consists on a SMA spring that contract and extend the earthworm muscle respectively. The proposed mechanism is simple but effective when traveling in narrow and rough environments, such as human digestive organs, bended long pipeline and so on. Also, this micro robot incorporates both control and power supply onboard. The theoretical speed of the micro robot is approximately 3.4*mm*/*cycle*, where the total time per cycle is 8*s* (the contraction time of the SMA is 2*s*, whereas the recovery time is 6*s*). The fabricated micro robot can move with the velocity of 10*mm*/*min* during 8 minutes. The stroke per cycle is 2.0*mm*.

#### *3.3.4. Other peristaltic motion concepts*

A concept similar to the one depicted in Figure 9 has been proposed in [48]. A SMA-spring has been used for changing the axial length of worm's modules, and consequently changing

their width. The robot has a length and diameter of 1*cm*. SMA springs of 50 and 100*μm* wires have been tested. The resulting prototype, made of 4 modules, was able to achieve a speed up to 0.22*mm*/*sec*, with a power consumption of 600*mA*. The previous prototype was composed of a number of identical segments attached in series, each of which alternately contract axially and expand radially. To conclude this section two prototypes are worth mentioning that use SMAs structures for peristaltic motion.

The proposed structure in these cases is a tubular mesh made of SMA wires that convert radial contraction into longitudinal lengthening. Such a structure has been proposed independently in [61] (see also [36]) and in the SoftWorm project [4].

**Figure 9.** Arrangement of Antagonistic circular muscles in Oligochaeta [48] (Image of the real Oligochaeta from http://en.wikipedia.org/wiki/Lumbricus\_terrestris).
