Toward a Gecko-Inspired, Climbing Soft Robot

Abstract

In this paper, we present a gecko-inspired soft robot that is able to climb inclined, flat surfaces. By changing the design of the previous version, the energy consumption of the robot could be reduced, and at the same time, its ability to climb and its speed of movement could be increased. As a result, the new prototype consumes only about a third of the energy of the previous version and manages to climb slopes of up to 84°. In the horizontal plane, its velocity could be increased from 2 to 6 cm/s. We also provide a detailed analysis of the robot's straight gait.

Keywords: apriltags; climbing robot; fast pneu-nets; gecko-inspired robot; mobile soft robots.

Figure 1

Current prototypes of the gecko-inspired soft robot. (A) Large prototype, (B) small prototype.

Figure 2

Explosion view of the small prototype of the gecko-inspired soft robot.

Figure 3

Control scheme: (A) Block diagram of the control loop for a single actuator. The block p(α) maps angle to pressure coordinates, C is the implemented PID controller, G₁ describes the dynamics of the proportional valve, and G₂ represents the dynamics of the tube and actuator. (B) Measured and fitted relation between bending angle and applied pressure in the horizontal plane of the left front leg of the small version.

Figure 4

Experimental setting. (A) Principal sketch, (B) apriltags attached to the robot's feet and torso's ends. The individual tags are indicated by different colors (red—front left, dark red—front right, orange—front center, dark orange—rear center, blue—rear left, dark blue—rear right).

Figure 5

Step response of a small (green) and a large (purple) soft actuator for a reference pressure of p_ref = 0.75 bar. The left graph shows the pressure and the right graph shows the angle response.

Figure 6

Analysis of the track of feet during one cycle of straight gait in the horizontal plane. (A) Track of large prototype, (B) track of small prototype. (C) Single frames show the abstraction of pose at the extreme points as well as in the start, middle, and end position during cycle. (D) Graph of orientation angle ε during cycle of small (green) and large (purple) prototype.

Figure 7

Gait patterns for straight movement of the robot. Fixed feet are indicated by filled circles and unfixed feet by unfilled circles. (A) Gait pattern for inclination angles δ < 70°. (B) Climbing pattern for high inclinations (δ ≥ 70°). Vacuum is applied to red and black filled feet. Black filled feet are fixed to the ground, whereas red feet do not necessarily have to be. In order to secure the fixation, the foot to be fixed is swinged back and forth once.

Figure 8

Maximum bending angle (A,B) and corresponding reference pressures (C,D) of front legs (red), rear legs (blue), and torso (orange) during a cycle. By applying the same pressure reference for different inclination angles (i.e., different loads), the dashed curves are obtained. The solid curves are obtained from the recalibrated pressure references, such that the bending angles match 90° as good as possible. Left diagrams are for large prototype and right diagrams for small prototype.

Figure 9

(A) Walking performance and (B) energy consumption for various inclination angles. Dashed curves show the values for constant and solid curves for recalibrated pressure references.