An antagonistic variable-stiffness pneumatic flexible joint.

This paper develops an antagonistic variable-stiffness pneumatic flexible joint in which two groups of artificial muscles are symmetrically distributed on both sides of the elastic thin plate. The elastic thin plate restricts the axial movement of the joint. Therefore, the joint can achieve single-dimensional and bidirectional bending by controlling the air pressure value of the pneumatic artificial muscle. Two variable stiffness elastic dampers are also symmetrically installed on both sides of the elastic thin plate, using a positive-pressure driving method to achieve real-time posture maintenance function of the joint based on particle-blockage, wedge structure, and antagonistic effect. The mathematical models for the bending angle and stiffness of flexible joints were established, and relevant experiments were conducted. When the air pressure of the pneumatic artificial muscle is 0.32 MPa, the joint bending angle reaches 62.7°. When the bending angle is 60° and the air pressure of the variable-stiffness elastic damper is 0.5 MPa, the stiffness in the bending direction of the flexible joint with the variable-stiffness elastic damper is 6.9 times that of the flexible joint without the variable-stiffness elastic damper, and the stiffness in the reverse bending direction is 10.3 times that of the flexible joint without the variable-stiffness elastic damper under the same conditions.

A Pneumatic Particle-Blocking Variable-Stiffness Actuator.

In order to improve the stiffness of flexible robots, this paper proposes a variable-stiffness elastic actuator. The actuator integrates the working principles of a pneumatic drive, wedge structure, and particle blockage. The anti-tensile stiffness of the actuator is nonlinearly negatively correlated with the air pressure because of the structural and material properties. The anti-compressive stiffness and lateral stiffness increase nonlinearly as air pressure increases, being 3 and 121 times greater at 0.17 MPa compared to 0 MPa, respectively. Beyond 0.17 MPa, the two stiffnesses of the actuator experience incremental growth due to wedge resistance forces.

Soft Humanoid Hands with Large Grasping Force Enabled by Flexible Hybrid Pneumatic Actuators.

Soft grippers and actuators have attracted increasing attention due to safer and more adaptable human-machine and environment-machine interactions than their rigid counterparts. In this study we present a novel soft humanoid hand that is capable of robustly grasping a variety of objects with different weights, sizes, shapes, textures, and stiffnesses. The soft hand fingers are made of flexible hybrid pneumatic actuators (FHPAs) designed based on a modular approach. A theoretical model is proposed to evaluate the bending deformation, grasping force, and loading capacity of the FHPAs, and the effects of various design parameters on the performance of the FHPA are investigated for optimizing the soft hands. This new FHPA achieves a balance of required flexibility and necessary stiffness, and the resulting soft humanoid hand has the merits of fast response, large grasping force, low cost, light weight, and ease of fabrication and repair, which shows promise for a variety of applications such as fruit picking, product packaging, and manipulation of fragile objects.