Overcoming Bistable Limitations
Traditional soft grippers offer passive adaptability but often require constant energy and respond slowly. Bistable mechanisms allow for fast, energy-free locking, but their energy thresholds are fixed at the design stage. That rigidity makes it hard to balance soft initiation and secure holding in one system.
The new gripper addresses this by using a motorized mechanism to adjust the curvature of a PET beam at its core. This curvature directly alters the energy landscape of the system, enabling real-time control over how easily the gripper snaps shut and how firmly it holds on.
Design and Testing
Constructed from a PET beam (50 mm long, 26 mm wide, 0.20 mm thick), the gripper integrates a slider-crank system driven by a small motor. Key structural parts were 3D-printed, while off-the-shelf components included the beam, motor, and rods.
To assess performance, the team used high-speed cameras (500 fps) to capture the gripper’s snapping motion and tested mechanical force-displacement behavior using a tensile machine. Results showed the gripper could snap shut in just 25 milliseconds and hold its position passively.
When tested on a drone, the system (totaling 132 g) enabled stable perching on various surfaces. The drone itself weighed 548 g and used optical flow sensing to manage height during landings.
Key Findings
During testing, the gripper proved both sensitive and strong, showing how well it can adapt to different tasks in real-world conditions.
- It needed just 0.66 newtons of force to trigger when pressed at the right point—light enough to safely interact with fragile objects.
- Adjusting the beam’s thickness by only 0.05 mm reduced the energy barrier by over 57 %, showing how finely the grip can be tuned.
- A specific curvature of 0.04 mm-1 was found to ensure the fingers lock tightly together with no gap, preventing slips during handling.
- Once the object is grasped, the system holds it without using any extra power, making it especially efficient for drones or mobile robots that run on limited energy.
These results highlight the gripper’s ability to respond gently when needed, then hold firm—all with minimal complexity and energy use.
Outlook
The gripper’s ability to switch between delicate and firm grasping without constant power makes it a strong candidate for mobile and aerial robotics, where energy efficiency and adaptability are critical. Future work will focus on replacing the motorized mechanism with smart materials to reduce weight and further enhance responsiveness—bringing this technology closer to real-world deployment in drones, robotic arms, and wearable devices.
Journal Reference
Zhang, J., Yang, H., He, C., Ma, H., Zhao, Y., Zhang, Z., Li, S., Wang, W., Yang, J., Wu, J., & Peng, H. (2025). Instant energy barrier modulation in bistable robotic grippers for compliant triggering and powerful grasping. Research, 8. DOI:10.34133/research.0737. https://spj.science.org/doi/10.34133/research.0737
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