HexaGripper: A Single-Actuator, Winch-Deployed Gripper for Autonomous Aerial Parcel Collection
Authors: Nimantha Adikaram, Mahen Abeyratne, Lakmina Chandrajith, A. H. T. E. De Silva, Isira Naotunna, Asanka Perera
Organizations: Department of Mechanical Engineering, University of Moratuwa, Moratuwa 10400, Sri Lanka. · School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, SA, Australia. · School of Science, Engineering and Digital Technologies, University of Southern Queensland, Australia.
Autonomous aerial parcel collection remains constrained by package-transfer operations that require manual loading, landing, or dedicated ground infrastructure. This letter presents HexaGripper, a single-actuator, winch-deployed six-plate gripper for autonomous collection of cuboid parcels. The proposed mechanism provides synchronized grasping with a wide capture region and tolerance to positional misalignment during pickup. The system integrates vision-based alignment, range sensing, winch deployment, and state-based control to enable autonomous collection while maintaining UAV separation from the pickup surface. Experimental evaluation covered static grasping, capture-workspace assessment, and end-to-end outdoor aerial collection. Static experiments achieved 100% pickup success (15/15 trials) across three parcel geometries, while workspace experiments achieved successful pickup at all 28 tested positions up to a 150 mm radial offset. End-to-end outdoor aerial collection achieved an 80% success rate (4/5 trials). These results demonstrate the feasibility of mechanically synchronized, winch-deployed grasping for landing-free autonomous aerial parcel collection.
Figures & tables
Fig. 1: HexaGripper system design and prototype: (a) integrated gripper-winch assembly and major components, (b) exploded view of winch assembly, (c) exploded view of the gripper assembly, and (d) fabricated physical prototype.
Fig. 2: HexaGripper prototype and UAV integration: (a) open six-plate configuration, (b) central cam and radial-extender mechanism, (c) assembled HexaGripper, (d) plate, connector, radial extender, and follower assembly showing the pin-in-slot mechanism, (e) initial plate configuration, (f) fully extended configuration after 90∘ plate rotation, and (g) integration with the UAV platform.
Criterion
Weight
Simple actuation
0.15
Low mass
0.15
Position-error tolerance
0.20
Repeatability and robustness
0.20
Low interference with UAV systems
0.15
Package and aircraft safety
0.15
TABLE I: Mechanical design-selection criteria
Fig. 3: Archimedean-spiral cam geometry showing the initial follower radius a , final radius a+L , cam rotation range 0≤θ≤β , and spiral centerline r(θ)=a+bθ .
Fig. 4: Evolution of the HexaGripper from the selected radial-cam concept to the final mechanism. The design progressed from radial-only plate translation to coupled radial translation and 90∘ plate rotation, with the six plate assemblies synchronized by a single cam and deployed using a worm-geared winch.
Fig. 5: Perception and control architecture with the state-based autonomous collection sequence. Visual target localization and range sensing guide UAV alignment and gripper deployment, while the controller coordinates winch and gripper actuation, grasp verification, and loaded recovery.
Fig. 6: Sequential operation of the winch-deployed gripper during parcel collection: (a-c) descent toward the parcel, (d-e) gripper opening and engagement, (f) parcel enclosure, and (g-h) winch retraction and parcel lifting.
Fig. 7: Predicted holding force across the cam radius at different servo torque levels.
Fig. 8: Finite-element stress analysis of (a) the gripper plate assembly under a 10 N gripping load and (b) the winch bearing bracket under a 30 N vertical load.
Fig. 9: Static grasp performance across the three parcel geometries: (a) trial-to-trial grasp-quality repeatability and (b) mean grasp-quality score with standard-deviation error bars.
Static Grasp Results
Box
L
W
H
Scores
Mean
(cm)
(cm)
(cm)
(Trial 1 to 5)
A
12.5
10.0
5.5
10, 10, 5, 10, 10
9.0
B
16.0
14.5
6.0
10, 10, 10, 10, 10
10.0
C
11.0
9.0
8.0
5, 5, 5, 10, 5
6.0
Workspace Grasp-Quality Results
TABLE II: Static and workspace grasp-quality results
Trial
Alignment
Deploy
Grasp
Recover
Overall
1
✓
✓
✓
✓
✓
2
✓
✓
✓
✓
✓
3
✓
✓
✗
-
✗
4
✓
✓
✓
✓
✓
5
✓
✓
✓
✓
✓
TABLE III: Real-world aerial collection results during UAV hovering.
Prior Works
Year
Application
Single Act.?
Tethered Deploy.?
Enclosure Grasp?
Position Tolerant?
Contact Elements
Gripper Mass (g)
Capture Offset (mm)
Aerial Success (%)
RAPTOR [ 13 ]
2022
Rapid aerial pickup
✗
✗
✗
✓
4
-
-
83
Linkage Gripper [ 3 ]
2023
Object pick-and-place
✓
✗
✗
✗
2
-
-
55
TRIGGER [ 22 ]
2023
Universal jamming
✗
✗
✓
✓
1
380
-
-
Modular Soft SAV [ 5 ]
2024
Grasping & landing
✓
✗
✓
✓
4
260
-
-
Multitentacle [ 12 ]
2024
Dynamic capture
✗
✗
✓
✓
12
-
-
-
Passive Dynamic [ 10 ]
2024
Dynamic perching
Passive
✗
✓
✓
2
150
40
-
TABLE IV: Comparative evaluation of representative aerial grasping and perching mechanisms.
Fig. 10: Grasp-quality workspace characterization: (a) measured 2-D grasp-quality map and (b) corresponding 3-D score surface. The experimentally demonstrated reliable grasp radius was 150 mm.
National Key Laboratory of Novel Software Technology, Nanjing University, Nanjing, China · School of Artificial Intelligence, Nanjing University, Nanjing, China · Faculty of Robot Science and Engineering, Northeastern University, China +1