Model-Based Control and External Load Estimation of an Extensible Soft Robotic Arm

An empirical model of soft bellows actuator

Soft robotics has emerged as a highly promising field, particularly for handling interactions in unstructured environments such as food factories and agricultural warehouses. This potential is largely attributed to the inherent flexibility and compliance of soft robots. A critical aspect in the development of these robots lies in the selection and utilization of appropriate soft actuators and materials. Nevertheless, the modeling of soft robots presents considerable challenges owing to their intricate properties and continuum nature. In this article, we focus on the design and modeling of a three dimensional (3D) printed soft bellows actuator. The primary objective is to assess its efficacy in creating suitable soft grippers for handling various practical products. We propose an empirical model to predict the output forces of the soft bellows actuator. This model comprehensively integrates parameters such as bellows geometry and material properties, thereby providing valuable insights for the actuator's design and control. To ascertain the precision of our model, we conducted a series of finite element simulations considering different designed parameters of the bellows, and performed experimental validations using 3D printed bellows actuators. The empirical model demonstrated high accuracy in predicting the output forces of the bellows actuator, with average absolute and relative errors of 1.35 N and 3.5 % , respectively. As an application, a robotic gripper with two parallel bellows actuators was developed, and its grasping force was validated using the empirical model. Building on this, a robotic gripper incorporating three bellows actuators was designed and fabricated based on the empirical model, and pick-and-place experiments were effectively conducted for handling a range of products.

Performance enhancement of the soft robotic segment for a trunk-like arm

Trunk-like continuum robots have wide applications in manipulation and locomotion. In particular, trunk-like soft arms exhibit high dexterity and adaptability very similar to the creatures of the natural world. However, owing to the continuum and soft bodies, their performance in payload and spatial movements is limited. In this paper, we investigate the influence of key design parameters on robotic performance. It is verified that a larger workspace, lateral stiffness, payload, and bending moment could be achieved with adjustments to soft materials' hardness, the height of module segments, and arrayed radius of actuators. Especially, a 55% increase in arrayed radius would enhance the lateral stiffness by 25% and a bending moment by 55%. An 80% increase in segment height would enlarge 112% of the elongation range and 70 % of the bending range. Around 200% and 150% increments in the segment's lateral stiffness and payload forces, respectively, could be obtained by tuning the hardness of soft materials. These relations enable the design customization of trunk-like soft arms, in which this tapering structure ensures stability via the stocky base for an impact reduction of 50% compared to that of the tip and ensures dexterity of the long tip for a relatively larger bending range of over 400% compared to that of the base. The complete methodology of the design concept, analytical models, simulation, and experiments is developed to offer comprehensive guidelines for trunk-like soft robotic design and enable high performance in robotic manipulation.