Variable Stiffness Soft Robotic Arm with Positive-Pressure Layer Jamming for Enhanced Load Capacity
Zekai Wu,,Xin Fu,,Daohui Zhang and Xingang Zhao
AI summary
Problem
Soft robotic arms typically suffer from low load-bearing capacity and fixed stiffness, limiting their use in high-interaction or heavy-load tasks. Existing variable stiffness solutions often rely on complex vacuum sealing or lack dynamic adjustability during operation.
Approach
The design embeds an inflatable silicone airbag within a stack of interleaved jamming plates inside a corrugated spring housing. By regulating internal air pressure, the system dynamically compresses the layers to modulate friction and overall structural stiffness on demand.
Key results
- Achieved ~100 N/mm tensile stiffness and >500 N load capacity at 30 kPa with six jamming layers
- Delivered a 70-fold stiffness increase and 20-fold load capacity boost over the unreinforced baseline
- Maintained 40° per-segment omnidirectional bending via tendon actuation under stiffened conditions
- Identified layer count and airbag hardness as primary drivers for stiffness modulation, with plate width having minimal impact
Why it matters
Enables soft manipulators to dynamically switch between compliance and high strength, making them viable for demanding human-robot interaction and industrial handling tasks.
Abstract
Soft robotic arms have attracted considerable attention in high-interaction scenarios owing to their intrinsic safety and adaptability. Nevertheless, their application is often limited by low load capacity. To address this issue, this paper introduces a layered jamming variable stiffness mechanism applicable to corrugated spring shell structures, which typically possess high torsional stiffness but inadequate tensile and bending rigidity. The proposed design integrates an internal airbag and a jamming plate interlayer within an external corrugated spring structure. By controlling the air pressure inside the bag, the normal pressure applied to the jamming layers can be precisely regulated, thereby enabling dynamic adjustment of the overall structural stiffness. Experimental results demonstrate that under an air pressure of 30 kPa, a six-layer jamming plate configuration achieves a tensile stiffness of approximately 100 N/mm and supports tensile loads exceeding 500 N. These values represent a 70-fold improvement in stiffness and a 20-fold increase in load capacity compared to the non-reinforced structure. Additionally, the system retains omnidirectional bending capability via tendon-driven actuation, with a maximum bending angle of 40° per segment. Multiple units can be serially connected to form a manipulator with an extended workspace. This study highlights the efficacy of the layered jamming mechanism in significantly enhancing the stiffness and load-bearing performance of flexible robotic arms, providing a viable solution for applications requiring both compliance and strength.