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Robust Underwater Grasping of Sloped Objects with a Waterproof Passive Adaptive Gripper
Jooyoung Hong, Daewon Hong, Joohyung Kim
TL;DR
Sloped or asymmetric household objects can roll or slip during grasping, especially underwater when friction is reduced. The paper presents a waterproof gripper that combines a passive rotational joint with variable-stiffness particle-jamming pads. It reports improved performance over rigid and fixed-joint baselines across dry and submerged evaluations.
Problem
Sloped or asymmetric everyday objects can cause torque-driven rolling and shear slip during grasping, challenges worsened by reduced friction in wet or submerged domestic settings.
Source: §I · p. 1Method
A waterproof gripper combines a passive rotational joint for global self-alignment with particle-jamming pads that adapt locally and stiffen under compression.
Source: §I · p. 1, B. Design Overview · p. 2, D. Passive Particle Jamming Pad · p. 3Results
Experiments report superior holding capability and grasp robustness compared with rigid-pad and fixed-joint baselines in dry and underwater conditions.
Source: §I · p. 2Takeaways & Limitations
The integrated gripper provides stable grasping of diverse geometries in challenging submerged conditions without external vacuum actuation.
Source: 5) Discussion · p. 5, §IV · p. 6
Abstract
from arXiv · showhide
Robust grasping of everyday objects remains challenging for parallel-jaw grippers, particularly when handling sloped or asymmetric items that induce torque-driven rolling and shear slip. These challenges become even more severe in domestic environments such as kitchens, where objects are often wet or submerged, drastically reducing friction between the gripper and the object. To address these issues, we present a waterproof passive adaptive gripper that combines local and global adaptability for high-performance grasping in the submerged environments. The proposed gripper features a fully waterproof design that integrates a passive rotational joint for global self-alignment on sloped surfaces and passive variable-stiffness pads for local surface adaptation. Experiments in both dry and underwater conditions on various cylindrical and conical objects demonstrate superior holding capability and grasp robustness compared to rigid-pad and fixed-joint baselines. The proposed design offers a practical and robust solution that successfully enables stable underwater manipulation of diverse everyday objects, effectively addressing a critical gap in current underwater robotic grasping for daily-life applications.
I. INTRODUCTION
Sloped or asymmetric household objects can roll or slip during grasping, with low underwater friction worsening the challenge. The paper combines global self-alignment, local variable-stiffness pads, and waterproof integration to improve grasping in dry and submerged conditions.
I. INTRODUCTION
- Wet, sloped or asymmetric items can trigger torque-driven rolling and tangential shear slip, leading to grasp failure under reduced underwater friction.Domestic tasks such as dish collecting and dishwasher loading require handling wet or submerged objects.Source: §I · p. 1
- Local compliance alone cannot neutralize force misalignment and offset torque on sloped, low-friction surfaces.The introduction notes that fixed-orientation adaptive fingertips deform locally but do not reorient the overall contact geometry.Source: §I · p. 1
- The proposed gripper combines a passive rotational joint for global alignment with particle-jamming pads for local adaptation and shear-resistant load bearing.The pads transition under compression without external vacuum.Source: §I · p. 1
- Experiments report improved holding capability and shear resistance over rigid-pad and fixed-joint baselines.The paper evaluates the gripper in dry and underwater conditions on various cylindrical and conical objects.Source: §I · p. 2
II. HARDWARE DESIGN
The hardware design is organized around mechanisms for local and global adaptability and waterproof operation. It describes the passive rotational joint, passive particle-jamming pads, and waterproof system integration.
II. HARDWARE DESIGN
- The hardware design targets grasping sloped kitchen items and describes mechanisms for local and global adaptability.The section also addresses waterproof system integration.Source: §II · p. 2
- The design includes a passive rotational joint as a key mechanism for robust underwater grasping.Source: §II · p. 2
- The design also includes passive particle-jamming pads and waterproof system integration.Source: §II · p. 2
A. Sloped Kitchen Items
The design targets sloped household items that can induce rolling and shear slip during grasping. It pairs a jaw designed for measured slopes with a hardware overview built around alignment, shear resistance, and waterproof operation.
A. Sloped Kitchen Items
- Household items have measured slopes up to approximately 20°, so the passive rotational jaw accommodates angles up to 30° to allow for pose error and geometric variation.Source: A. Sloped Kitchen Items · p. 2
- Sloped geometry can produce off-axis torques and unstable point or line contacts, which translate into tangential shear, rolling, pose drift, or slip.Source: A. Sloped Kitchen Items · p. 2
B. Design Overview
- The hardware overview assigns self-alignment to a passive rotational joint, shear resistance to particle-jamming pads, and submerged operation to waterproof integration.The pads enlarge contact area during initial closure and stiffen under further compression.Source: B. Design Overview · p. 2, Figure 3 · p. 2
C. Passive Rotational Joint
The passive rotational joint aligns the jaw to sloped surfaces, while particle-jamming pads conform locally and stiffen under compression. The pad’s grooved membrane also channels fluid away from submerged contacts.
C. Passive Rotational Joint
- Elastic ligaments let the distal frame rotate on sloped surfaces, reducing angular mismatch and shifting contact from an edge or line toward distributed surface contact.Source: C. Passive Rotational Joint · p. 3
- The joint supports rotation up to approximately 30°, exceeding measured household slopes and providing margin for irregular geometries and grasp perturbations.Its ligament stiffness also returns the jaw to a neutral pose when unloaded.Source: C. Passive Rotational Joint · p. 3
D. Passive Particle Jamming Pad
- The waterproof TPU membrane and coffee-particle filling conform during initial contact, then jam under compression to increase stiffness and shear resistance.The mechanism extends passive particle-jamming adaptation to submerged grasping of sloped objects.Source: D. Passive Particle Jamming Pad · p. 3
- TPU membrane elasticity passively restores the pad and redistributes its particles upon release, while grooves drain trapped fluid to improve submerged shear resistance.The recovery resets the pad without external pneumatic systems; groove benefits depend on object geometry and contact conditions.Source: D. Passive Particle Jamming Pad · p. 3
E. Waterproof Integration
Waterproof actuation and a sealed camera enclosure support the gripper’s submerged operation while preserving visual observation.
E. Waterproof Integration
- Waterproof actuators were selected to avoid common failure modes associated with custom-sealed actuation structures.The gripper is designed for submerged operation.Source: E. Waterproof Integration · p. 3
- A custom watertight housing encloses the USB camera, with a cable gland sealing the cable pass-through.The gland is designed to preserve flexibility and durability during repeated assembly and use.Source: E. Waterproof Integration · p. 3
- Front and rear O-ring interfaces provide repeatable sealing, while a transparent acrylic window maintains camera visibility.At the front interface, the window compresses the O-ring against the housing.Source: E. Waterproof Integration · p. 3
III. EXPERIMENTS
The experiments measure holding force during controlled pulls in dry and submerged conditions, using varied pad designs and cylindrical or conical objects.
III. EXPERIMENTS
- Holding force was measured as the mean of 10 pulls per object in dry and submerged conditions.The experiments quantify how underwater operation affects holding capability.Source: §III · p. 3
A. Experimental Setup
- The pulling setup uses a fixed gripper, identical commanded current values, and a motor-driven wire to pull objects horizontally.The load cell records peak force; pulls proceed at 7.0 mm/s, and submerged trials use static clear water to isolate gripper mechanics from hydrodynamic disturbances.Source: A. Experimental Setup · pp. 3–4, Figure 5 · p. 4
- Grooved and flat particle-jamming pads were compared with a rigid PLA-insert pad, using the same TPU outer membrane across pads.The shared membrane keeps surface friction consistent across conditions.Source: A. Experimental Setup · p. 4
- Tests used cylindrical objects and 10° and 20° conical objects across varying diameters.Only two 20° cones were used because larger-side diameters exceeded the gripper’s effective grasp range; Fig. 5 depicts the objects and pad types.Source: A. Experimental Setup · p. 4, Figure 5 · p. 4
B. Holding Force
Across design variants, the experiments examine holding-force contributions from the passive rotational joint, particle-jamming pad, and surface pattern; the free joint outperformed the fixed-joint baseline.
B. Holding Force
- Ten independent pulling trials per object were used to compare variants and isolate the three design contributions.In submerged tests, the rigid pad succeeded only for Markers 1 and 2, and every pad configuration failed on the largest cones at the steepest angles.Source: B. Holding Force · p. 4
1) Passive rotational joint:
- 9.75 N versus 7.71 N, the free-joint configuration achieved a 26.5% higher overall mean holding force than the fixed-joint baseline.The authors attribute the improvement to passive self-alignment reducing tangential shear and preventing off-axis rolling on sloped surfaces.Source: 1) Passive rotational joint · p. 4
2) Particle jamming pad:
Particle-jamming pads outperform rigid pads in both dry and submerged tests, while the preferred surface pattern varies with object geometry.
2) Particle jamming pad:
- 7.41 N versus 3.70 N, the flat jamming pad outperformed the rigid pad underwater; in dry conditions, the corresponding forces were 13.65 N versus 6.66 N.The authors report reduced holding forces for all pad variants underwater, alongside a jamming-pad advantage over the rigid baseline.Source: 2) Particle jamming pad · pp. 4–5
3) Surface pattern:
- Grooves raised Marker 1 holding force by 61.8% to 23.40 N from 14.46 N, but lowered Marker 12 force by 42.4% to 8.36 N from 14.51 N.The grooved pad had a slight average advantage in dry and submerged conditions, while the flat pad could better suit highly sloped objects needing continuous conformal contact.Source: 3) Surface pattern · p. 5
4) Object-wise performance:
- Markers 1–4 are cylindrical, Markers 7–10 are 10° cones, and Markers 11–12 are 20° cones; the joint’s largest gains were on highly tapered objects.There, the shift from unstable point contact to stable surface contact was the primary factor; on cylinders, grooves dominated through geometric interlocking.Source: 4) Object-wise performance · p. 5
- Higher standard deviations in some cases indicate sensitivity to initial contact configuration and stochastic local interactions, especially sudden torque-induced rolling.The reported variability concerns TPU-membrane interactions with object geometry.Source: 4) Object-wise performance · p. 5
5) Discussion:
The gripper combines rotational self-alignment with variable-stiffness jamming to stabilize underwater grasps. Surface-groove benefits vary with object geometry, while camera-detected markers track underwater object movement.
5) Discussion:
- The rotational joint aligns the gripper with conical surfaces to reduce shearing torques, after which the particle-jamming pad locks the object's geometry.The pad acts as a fine adaptation layer once the contact face is aligned.Source: 5) Discussion · p. 5
- The underwater setup uses a camera inside the waterproof housing to detect object markers and track movement.Table II reports object pose and speed change under water.Source: Figure 7 · p. 5, Table II · p. 5
- Grooves can aid cylindrical grasps through interlocking but may reduce continuous contact on steep cones, making their benefit object-dependent.The trade-off is between geometric interlocking and conformal contact area.Source: 5) Discussion · p. 5
- Combining self-alignment with variable-stiffness jamming compensates for reduced frictional margins during underwater manipulation.The paper presents the integration as a robust approach for diverse geometries in submerged conditions.Source: 5) Discussion · p. 5
C. Underwater Item Grasping
Underwater trials showed that displacement and slip depended on object geometry and buoyancy. Rigid cans and tumblers moved less than dishes, while buoyant objects also showed greater rotational variation.
C. Underwater Item Grasping
- The test set included sloped kitchenware, plates, and bowls, and the gripper was manually operated while its alignment and jamming mechanisms acted passively.The pick-and-place protocol moved each object to the tank center before release.Source: C. Underwater Item Grasping · p. 5
- Buoyant items, including plastic cups and light dishes, were transported while floating, indicating holding under hydrodynamic disturbances.Source: C. Underwater Item Grasping · p. 6
- Pose and velocity changes were measured from steady grasp to release, with temporary marker losses linearly interpolated and each object tested in five trials.Reported mean pose and velocity changes accumulated increases and decreases in magnitude.Source: C. Underwater Item Grasping · p. 6
- Rigid cylindrical or conical items stayed within 5 mm positional displacement, with average slip speeds under 1.5 mm/s; large and small dishes shifted 11–14 mm at 2.0–3.2 mm/s.Conical contact areas helped the jamming pad suppress translational slip, while thin-walled dishes had less effective contact area.Source: C. Underwater Item Grasping · p. 6
- Dense items maintained orientation changes under 15 deg and rotational speeds below 4 deg/s, whereas lightweight plastic items rotated up to 48 deg and exceeded 10 deg/s.The paper attributes the greater rotational variation to buoyant forces and hydrodynamic drag during transport.Source: C. Underwater Item Grasping · p. 6
IV. CONCLUSION
The paper presents a waterproof passive gripper combining rotational self-alignment with particle-filled pads that increase shear robustness under compression. Evaluations in dry and submerged conditions report better performance than rigid and fixed-joint baselines; closed-loop grasp regulation remains future work.
IV. CONCLUSION
- The design pairs a passive rotational joint for global self-alignment with particle-filled pads that change stiffness and improve shear robustness under compression.The integrated performance is achieved without external vacuum actuation.Source: §IV · p. 6
- Evaluations in dry and submerged conditions found superior performance to conventional rigid and fixed-joint baselines.The reported evaluation spans diverse kitchenware configurations.Source: §IV · p. 6
- The waterproof system enabled reliable submerged actuation and clear in-hand camera views for underwater object monitoring.Source: §IV · p. 6
- Future work will integrate in-hand visual or tactile feedback for closed-loop detection and mitigation of incipient slip during autonomous underwater manipulation.The stated aim is to improve stability across a wider range of object sizes and slope angles.Source: §IV · p. 6