A Spider-Joint-like Bionic Actuator with an Approximately Triangular Prism Shape

Abstract

The unique drive principle and strong manipulation ability of spider legs have led to several bionic robot designs. However, some parameters of bionic actuators still need to be improved, such as torque. Inspired by the hydraulic drive principle of spider legs, this paper describes the design of a bionic actuator characterized by the use of air pressure on each surface and its transmittance in the direction of movement, achieving a torque amplification effect. The produced torque is as high as 4.78 N m. In addition, its torque characteristics during folding motions are similar to those during unfolding motions, showing that the bionic actuator has stable bidirectional drive capability.

Keywords: actuator; bionic; fluidic; soft robot; spider inspired.

Figure 1

(a) Spider joint shape for joint membrane folding.(b) The joint membrane unfolds when the spider’s legs extend. (c) The joint membrane folds when the spider’s legs bend. (d) Bioinspired actuator. (e) The bionic actuator allows the mechanical arm to lift a 500 g hammer. The torque of gravity during the ascent of the mechanical arm and the torque of the bionic actuator increase as the angle increases. The mechanical arm can rise stably with a constant pressure of 4 kpa.

Figure 2

(a) The unfolding form of the structure: the dotted line is a crease, and all the edges and creases are soft. (b) The approximate triangular prism origami structure to be folded, wherein the triangular plane may be concave or convex. (c) α is the angle between two working planes, and P is the input air pressure. When the bionic actuator is inflated, the two working planes unfold, and α increases.

Figure 3

(a) The structure of the partially folded bionic actuator. At this time, the triangular plane and rectangular plane II are partially folded, and the triangular plane changes into a quadrangular pyramid shape. (b) The force of the bionic actuator is analyzed using a simplified mechanical model. The relationship between (c) torque (M) and angle (α) and (d) angle (α) and volume (V) after calculation and analysis.

Figure 4

(a) The working principle of DLP printing technology. (b) The soft actuator body processed using 3D printing. (c) The soft actuator body structure and rigid carbon fiber plate are bonded using an adhesive to form a rigid and soft bionic actuator.

Figure 5

Comparison of theoretical analysis results with experimental results. (a) Testing device. (b) Measurement of the output torque (M) at pressures from 1 to 10 kPa and angles (α) from 15° to 35°. The results show that the torque (M) increases with increasing pressure, and the torque rate increases with increasing pressure. (c) Based on the data analysis, when the pressures are 1, 4, and 7 kPa, the larger the angle (α) at the same pressures, the greater the output torque.(d) Comparison of theoretical analysis and experimental results.

Figure 6

(a) Simplified stress diagram. (b) Correlation between torque (M) and inner vacuum degree (P). When folding, P represents the pressure difference between the inside and outside, reflecting the pulling force generated by the vacuum. (c) The results for torque (M) change trends during unfolding and folding, which are similar.

Figure 7

(a) Rectangular plane II is divided into plane II (1) and plane II (2) along the crease, and the force (F) applied by the load is transmitted through plane II (2) to plane II (1). Force $F_1$ is generated in plane II (1), turning it counterclockwise so that the bionic actuator cannot maintain its original shape. The transmission angle $(\gamma )$ when transmitted from plane II (2) to plane II (1) is shown in the figure. (b) Experimental verification. (c) Experimental result.

Figure 8

(a) The triangular plane may be concave or convex. (b) When $H_0$ is positive under the same pressure, the smaller $H_0$, the larger the actuator output torque (M).