A soft robotic spine with tunable stiffness based on integrated ball joint and particle jamming

• A soft robotic arm with high flexibility and variable stiffness.
• Integrated ball joint spine and particle jamming.
• Particle rearrangement and deformation inherent of particle jamming cause no problems in the proposed mechanism.
• Controllable repeatability and large rigidity range with quick response can be achieved.

Highly flexible soft robotic arms are safe for human–machine interaction. Particle Jamming has been demonstrated to be very effective for soft robotic arms with stiffness modulation by pneumatic means. However, the structural uncertainty due to particle re-organization makes particle jamming based soft robotic arms unreliable in both position and stiffness control. Ball joint based robotic arms have good structural integrity and good positional control property. Yet their stiffness modulation is very difficult. Instead of modulating stiffness using wires, this research proposes stiffness modulation of ball joint based robotic spines using vacuum energy. To strengthen the spine arm stiffness, particles are integrated into the ball joint spine. Both analysis and experimental studies in this research have shown that the integrated robotic spine has much better performance in terms of stiffness compared to the ball joint based spine without particle jamming. In fact, experimental studies have shown stiffness enhancement of 13 times. The proposed soft robotic spine can be used in applications where a large band of stiffness modulation is required.