A Soft Continuum Robot with Self-Controllable Variable Curvature

TL;DR

This work addresses the lack of continuous curvature control in soft continuum robots by introducing SCoReS, which uses a self-contained growing spine and granular jamming to vary stiffness along the body. The authors model the jammed spine using Euler-Bernoulli beam theory, with $M = -E I (d^2 y/dx^2)$ and $I = pi r^4/4$, and relate end-load deflection to material stiffness through $E = 4 F L^3/(3 pi r^4 y)$, while coupling this stiffness to a finite-element model in Abaqus. Finite element analysis in conjunction with experiments validates that aging or length changes of the jammed spine produce distinct bending profiles and end-effector trajectories, corroborated by a 3D demonstration including a fruit-grasping task. The main contributions are the novel self-contained variable-curvature design, a growing spine with granular-jamming control, and the combined modeling and experimental validation showing versatile, three-dimensional bending in constrained environments. The practical impact lies in enabling more dexterous manipulation in restricted or cluttered settings with fewer actuators and lower design complexity.

Abstract

This paper introduces a new type of soft continuum robot, called SCoReS, which is capable of self-controlling continuously its curvature at the segment level; in contrast to previous designs which either require external forces or machine elements, or whose variable curvature capabilities are discrete -- depending on the number of locking mechanisms and segments. The ability to have a variable curvature, whose control is continuous and independent from external factors, makes a soft continuum robot more adaptive in constrained environments, similar to what is observed in nature in the elephant's trunk or ostrich's neck for instance which exhibit multiple curvatures. To this end, our soft continuum robot enables reconfigurable variable curvatures utilizing a variable stiffness growing spine based on micro-particle granular jamming for the first time. We detail the design of the proposed robot, presenting its modeling through beam theory and FEA simulation -- which is validated through experiments. The robot's versatile bending profiles are then explored in experiments and an application to grasp fruits at different configurations is demonstrated.

Figures (9)

• Figure 1: (A) Illustration of controllable curvatures when the robot is pressurized at 250kPa. (B) Inner structure: The soft continuum robot has a hollow channel that allows the growing spine to travel inside. The jammed spine then creates a high stiffness inside while the remaining length is flexible. With the same control inputs, it creates different bending profiles. (C) Realizing concept: The growing spine filled with granules changes length using positive pressure and length control. Using negative pressure, it increases stiffness by granular jamming.
• Figure 2: (A) Fabrication of the soft continuum robot: silicone mixing, degassing, winding strings on the rod, molding silicone for each tube, assembling all the tubes for a single section continuum robot. (B) Dimension of the soft continuum robot. It has nine chambers, and each three of them are connected.
• Figure 3: System detailed design (A) 1. Experimental Setup, with a motion tracking system to track its end-effector positions and rotations. 2. Cross-section area to show the inner structure of the robot. Inside the steel box, airtight fabric divides the volume into two. The bottom volume contains glass bubbles and a length control mechanism. The filter paper on top of the pegboard prevents glass bubbles from going into the vacuum chamber when jamming. 3. Detailed length control mechanism: using a stepper motor for precise length control. (B) The state transitions to allow the SCoReS to reconfigure.
• Figure 4: (A) Control diagram of the overall system. (B) Detailed physical components: Electric Proportional Regulators, Step Motor Driver, Digital Analog Converter (DAC) for Proportional Regulators, Arduino and Solenoid Valves .
• Figure 5: (A) Experimental setup for bending experiments with load cell mounted on UR5. (B) Experimental setup for measuring length control with transparent tube and ruler.