2.2. Hexapod robot

The fabricated hexapod robot is displayed in Figure 3. The robot is 4.0 mm wide, 2.7 mm long, and 2.5 mm high. Two ground (GND) wires and eight signal wires (all made of copper) extend above the robot. The hexapod robot walks when the signal wires are connected to the hardware ANNs. The structure and stepping motion of the robot mimic those of an ant. The antlike stepping motion is a series of tripod configurations in which two groups of three legs alternate between swing and stance phases (see Figure 5 in [29]). The hexapod robot comprises

Figure 1. Image of the constructed quadruped robot.


Figure 2. Relative phase difference of quadruped gait patterns for different driving rhythms of the actuators. LF, RF, LH, and RH refer to left forelimb, right forelimb, left hindlimb, and right hindlimb, respectively.

the frame parts, small-sized actuators, and link mechanisms. The small-sized actuators are constructed from artificial muscle wire. All mechanical parts are made from silicon wafers of various thicknesses (100, 200, 385, and 500 μm). The parts were shaped by dry etching by photolithography-based inductively coupled plasma [30]. The small-sized actuator consists of four pieces of artificial muscle wire, as well as the shaft, rotor, and GND wire. The frame components and rotors are connected by the artificial muscle wire, which functions as a shape memory alloy [31]. The artificial muscle wire is BMX50 (BioMetal® Helix, available online at http://www.toki.co.jp [32]). The mechanical components of the hexapod robot are detailed in previous works [27, 29].

Figure 4 shows the leg motions of the hexapod robot. The artificial muscle wire shrinks at high temperatures and extends at low temperatures. Therefore, when an electric current is applied through the wire, the resulting heat displaces the four pieces of artificial muscle wire, and the rotor rotates. The wire is cooled by stopping the current flow. Thus, the actuator is rotated by changing the sequence of the input current. The link mechanism transmits the rotational movements of the rotor to the three legs on one side. This design requires only two small-sized actuators (one on each side of the robot) to actuate the six legs.

Gait Generation of Multilegged Robots by using Hardware Artificial Neural Networks http://dx.doi.org/10.5772/intechopen.70693 33

Figure 3. Image of the constructed hexapod robot.

Figure 4. Leg motions of the hexapod robot.

the frame parts, small-sized actuators, and link mechanisms. The small-sized actuators are constructed from artificial muscle wire. All mechanical parts are made from silicon wafers of various thicknesses (100, 200, 385, and 500 μm). The parts were shaped by dry etching by photolithography-based inductively coupled plasma [30]. The small-sized actuator consists of four pieces of artificial muscle wire, as well as the shaft, rotor, and GND wire. The frame components and rotors are connected by the artificial muscle wire, which functions as a shape memory alloy [31]. The artificial muscle wire is BMX50 (BioMetal® Helix, available online at http://www.toki.co.jp [32]). The mechanical components of the hexapod robot are detailed in

Figure 2. Relative phase difference of quadruped gait patterns for different driving rhythms of the actuators. LF, RF, LH,

and RH refer to left forelimb, right forelimb, left hindlimb, and right hindlimb, respectively.

Figure 4 shows the leg motions of the hexapod robot. The artificial muscle wire shrinks at high temperatures and extends at low temperatures. Therefore, when an electric current is applied through the wire, the resulting heat displaces the four pieces of artificial muscle wire, and the rotor rotates. The wire is cooled by stopping the current flow. Thus, the actuator is rotated by changing the sequence of the input current. The link mechanism transmits the rotational movements of the rotor to the three legs on one side. This design requires only two small-sized actuators (one on each side of the robot) to actuate

previous works [27, 29].

32 Advanced Applications for Artificial Neural Networks

the six legs.


Figure 5. Relative phase difference of hexapod gait patterns for different driving rhythms of the actuator.

Figure 5 shows the relative phase differences of the hexapod gait patterns for different driving rhythms of the actuator. To heat the artificial muscle wires, an input pulse of amplitude 50– 100 mA, period 2 s, and width 0.5 s is required. Therefore, the hexapod robot requires 2 s to complete one locomotion cycle. As mentioned above, the length of the artificial muscle wire depends on the temperature. Specifically, the wire shrinks when heated and extends when cooled. Heating the artificial muscle wires from A to D and from D to A in Figure 4 drives the hexapod robot forward and backward, respectively. The locomotion pattern is a 180 phase shift at each side, which mimics the locomotion of an ant. If the input pulse is narrower than 0.5 s, the thermal heating by the driving current is insufficient to shrink the wire. By contrast, if the input pulse is wider than 2 s, the thermal heating by the driving current is excessive, and the cooling is insufficient to extend the wire.
