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Integration of a Variable Stiffness Link for Long-Reach Aerial Manipulation

Manuel J. Fernandez, Alejandro Suarez, Anibal Ollero, Matteo Fumagalli

TL;DR

This work tackles the problem of balancing disturbance rejection and precision in long-reach aerial manipulation by introducing a cable-driven Variable Stiffness Link (VSL) that can switch between flexible and rigid coupling between a quadrotor and the LiCAS dual-arm manipulator. The approach combines hardware integration (1 m VSL, LiCAS A1) with a teleoperation framework and a dynamic model that captures the coupled UAV–payload system. Experimental results show that the flexible state attenuates disturbances and vibrations, while the rigid state enhances end-effector accuracy during manipulation, with transition times around 7.8 s and robustness under a 2 kg payload. The findings demonstrate the feasibility of adjustable stiffness for safer, more capable long-reach aerial manipulation and highlight avenues for autonomous stiffness control and cooperative multi-robot tasks.

Abstract

This paper presents the integration of a Variable Stiffness Link (VSL) for long-reach aerial manipulation, enabling adaptable mechanical coupling between an aerial multirotor platform and a dual-arm manipulator. Conventional long-reach manipulation systems rely on rigid or cable connections, which limit precision or transmit disturbances to the aerial vehicle. The proposed VSL introduces an adjustable stiffness mechanism that allows the link to behave either as a flexible rope or as a rigid rod, depending on task requirements. The system is mounted on a quadrotor equipped with the LiCAS dual-arm manipulator and evaluated through teleoperated experiments, involving external disturbances and parcel transportation tasks. Results demonstrate that varying the link stiffness significantly modifies the dynamic interaction between the UAV and the payload. The flexible configuration attenuates external impacts and aerodynamic perturbations, while the rigid configuration improves positional accuracy during manipulation phases. These results confirm that VSL enhances versatility and safety, providing a controllable trade-off between compliance and precision. Future work will focus on autonomous stiffness regulation, multi-rope configurations, cooperative aerial manipulation and user studies to further assess its impact on teleoperated and semi-autonomous aerial tasks.

Integration of a Variable Stiffness Link for Long-Reach Aerial Manipulation

TL;DR

This work tackles the problem of balancing disturbance rejection and precision in long-reach aerial manipulation by introducing a cable-driven Variable Stiffness Link (VSL) that can switch between flexible and rigid coupling between a quadrotor and the LiCAS dual-arm manipulator. The approach combines hardware integration (1 m VSL, LiCAS A1) with a teleoperation framework and a dynamic model that captures the coupled UAV–payload system. Experimental results show that the flexible state attenuates disturbances and vibrations, while the rigid state enhances end-effector accuracy during manipulation, with transition times around 7.8 s and robustness under a 2 kg payload. The findings demonstrate the feasibility of adjustable stiffness for safer, more capable long-reach aerial manipulation and highlight avenues for autonomous stiffness control and cooperative multi-robot tasks.

Abstract

This paper presents the integration of a Variable Stiffness Link (VSL) for long-reach aerial manipulation, enabling adaptable mechanical coupling between an aerial multirotor platform and a dual-arm manipulator. Conventional long-reach manipulation systems rely on rigid or cable connections, which limit precision or transmit disturbances to the aerial vehicle. The proposed VSL introduces an adjustable stiffness mechanism that allows the link to behave either as a flexible rope or as a rigid rod, depending on task requirements. The system is mounted on a quadrotor equipped with the LiCAS dual-arm manipulator and evaluated through teleoperated experiments, involving external disturbances and parcel transportation tasks. Results demonstrate that varying the link stiffness significantly modifies the dynamic interaction between the UAV and the payload. The flexible configuration attenuates external impacts and aerodynamic perturbations, while the rigid configuration improves positional accuracy during manipulation phases. These results confirm that VSL enhances versatility and safety, providing a controllable trade-off between compliance and precision. Future work will focus on autonomous stiffness regulation, multi-rope configurations, cooperative aerial manipulation and user studies to further assess its impact on teleoperated and semi-autonomous aerial tasks.
Paper Structure (15 sections, 6 equations, 24 figures)

This paper contains 15 sections, 6 equations, 24 figures.

Table of Contents

  1. INTRODUCTION
  2. SYSTEM OVERVIEW
  3. Aerial system
  4. Variable Stiffness Link
  5. Manipulator
  6. System architecture
  7. Control Strategy
  8. MODELING
  9. EXPERIMENTS RESULTS
  10. Disturbance rejection
  11. Aerial manipulation
  12. VSl standalone
  13. LiCAS integration
  14. CONCLUSIONS AND FUTURE WORK
  15. ACKNOWLEDGMENT

Figures (24)

  • Figure 1: Aerial manipulator - VSL connects the aerial system with the LiCAS dual-arm manipulator
  • Figure 2: VSL mounted on a workbench with a testing weight on the tip (left), sketch of VSL in rest configuration (middle) and bent state (right)
  • Figure 3: Mounting point detail of VSL under the aerial system
  • Figure 4: Operator with LiCAS AC1 teleoperation system (left) and dual-arm manipulator LiCAS A1 mounted on the aerial system (right)
  • Figure 5: System architecture diagram
  • ...and 19 more figures