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Biologically Inspired Robotics
derived from the reciprocal value of the snake-like robot axial distance 1/l axis
(l axis is the distance of the snake-like robot along its axial axis), changed with
respect to increased driving input. Here we take one S-shape for locomotion
and the other parameters are fixed at the values given in Table 2.1.
2.4.2 Control of the Locomotion Speed
Robot speed is mainly affected by locomotion frequency. As stated in Section
2.3.2, the period of CPG output maintains a linear relationship with the time
constant. Thus, the speed of the robot can be controlled by proportionally
adjusting the time constant. Herein, time constant τ 1 and τ 2 are adjusted with
the value of τ 1 /τ 2 kept at a constant. From the result of the simulation shown
in Figure 2.7b, we find that the motion speed decreases with an increasing in
the time constant, because this increase makes the period of the CPG output
become longer.
2.4.3 Control of the Number of S-Shapes
The number of S-shapes is an important motion parameter in snake-like
locomotion and describes the number of periods of the sinusoidal wave
existing in a snake-like locomotion shape. Based on the above analysis, we
changed the CPG network by different feedback connections to obtain the
desired number of locomotive S-shapes. For a snake-like robot with thirteen joints in the simulation, when connecting the twelfth CPG module with
the first one, the robot can generate only one S-shape, shown in Figure 2.8a;
when connecting the sixth CPG module with the first one, it can generate
(a)
2
1
3
6
4
12
13
(b)
(a)
(b)
FIGURE 2.8
Number of S-shapes changed through feeding different CPG modules: (a) one S-shape and (b)
two S-shapes.