This article proposes the concept design of a novel bio-inspired dual-axis compliant micromanipulator with millimeter working strokes dedicated to fiber alignment. It subtly mimics the gripping and ...rubbing function of human hand consisting of forefinger, purlicue, and thumb. As compared with traditional dual-axis gripper, its advantages lie in millimeter-level stroke, bidirectional rotation, less slippage, and comprehensive force sensing. To achieve dexterous and reliable manipulation, a two-degree of freedom flexible decoupling mechanism and a displacement reversing mechanism based on the leaf-shaped flexible hinge are introduced. Analytical models are derived to assess the statics and dynamics properties of the micromanipulator, which are verified by conducting finite-element analysis simulation study. A prototype driven by two voice coil motors is fabricated for experimental testing. Three high-precision strain gauges with temperature compensation are glued on the sensitive region to measure the gripping force and rubbing force. Experimental results show that the gripping stroke and rubbing stroke of the manipulator are up to 2.3 and 2.1 mm, respectively. For operating a custom-made fiber flag with a diameter of 200 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m, a rotation stroke of more than 1000<inline-formula><tex-math notation="LaTeX">^{\circ }</tex-math></inline-formula> has been achieved, which cannot be realized by previous work with the same level of compact mechanism design.
This article develops model-based grasp planning algorithms. It focuses on industrial end-effectors like grippers and suction cups, and plans grasp configurations considering computer aided design ...(CAD) models of target objects. The developed algorithms can stably find many high-quality grasps, with satisfying precision and little dependency on the quality of CAD models. The undergoing core technique is superimposed segmentation, which preprocesses a mesh model by peeling it into superimposed facets. The algorithms use the facets to locate contacts and synthesize grasp poses for popular industrial end-effectors. Several tunable parameters are prepared to adapt the algorithms to meet various requirements. The experimental section studies the influence of the tunable parameters and analyzes the cost, precision, and robustness of the proposed algorithms and their planned grasps, with both simulations and real-world systems. Besides, the proposed algorithms are applicable to mesh models reconstructed from point clouds obtained by depth sensors. Some experiments and analysis are also carried out to study and demonstrate the ability.
Recently, various soft universal grippers have been developed due to their reduced control complexity and satisfying grasping capability. The gripping range of a gripper plays a key role in its ...universality. This article presents a pneumatically actuated soft-rigid hybrid multifinger gripper that has a wide gripping range by adjusting its initial grasp postures. The gripper is compact (dimensions: <inline-formula><tex-math notation="LaTeX">\text{100} \times \text{60} \times \text{170}</tex-math></inline-formula> mm), lightweight (weight: 380 g), and modular. It consists of four modules, with each module containing three pneumatic actuators (a distance-adjusting actuator, an angle-adjusting actuator, and a finger actuator) and rigid connectors. Through initial grasp posture adjustment, and fingers with tapered angles to generate nonconstant bending while grasping, the gripper can grasp objects of a wide variety of sizes and weights, thus increasing its universality. The gripper is tested to characterize its distance adjustment range, angle adjustment range, and stiffnesses in load-bearing directions, at continuously changing pneumatic pressures. The distance adjustment range and angle adjustment range of the gripper are 0-64.4 mm (64.4% of the initial gripper length) and 0<inline-formula><tex-math notation="LaTeX">^{\circ}</tex-math></inline-formula>-140<inline-formula><tex-math notation="LaTeX">^{\circ}</tex-math></inline-formula>, respectively. The maximum stiffnesses of distance-adjusting actuator and angle-adjusting actuator are 3331 and 1.15 N<inline-formula><tex-math notation="LaTeX">\cdot</tex-math></inline-formula>m/rad, respectively. Finally, grasping experiments show that our gripper can successfully grasp objects with diameters ranging from 0.5 to 180 mm, lengths ranging from 10 to 325 mm, and the heaviest object it can grasp is 2.1 kg (more than five folds of its own weight). The results demonstrated that our pneumatic gripper has an increased gripping range without adding other types of energy sources and its enhanced universality will expedite various applications in daily life and industry.
This study presented a prestressed soft gripper fabricated with 3-D printing technology. The gripper can realize a large contact area while grasping and simultaneously generate large initial opening ...without deflating the soft actuators. The soft actuator was 3-D printed as two separate parts: the soft chambers with a rigid connector and a cover to seal the chambers. The chamber part was stretched longitudinally and sealed by gluing the cover onto it. The actuator was then released, and an initial curl occurred due to the remaining prestress. Finite element (FE) simulations were performed to validate this concept and the designed structure. Actuator fabrication and experimental tests were presented, and agreements between the FE simulations and test results were achieved. A gripper consisting of four prestressed actuators was constructed and experimentally tested by picking-and-placing food materials in different weights and different sized containers. To adapt to objects of different sizes and shapes, the gripper base was designed to have two configurations and two openings. The results showed that the prestressed gripper could stably handle various types of food and still remain compact with a simple supporting system.
This paper introduces the concept of underactuated vacuum gripper (UVG), which combines two strategies, that is, underactuation and vacuum grasping. The idea is to achieve shape adaptation while ...improving grip stability by augmenting an underactuated gripper with suction cups. A general theory to predict the contact forces for a UVG is developed and used for comparison reasons with a standard underactuated counterpart. Multibody simulations have been performed to verify the analytical model and quantitatively evaluate the performance of the system in terms of three metrics, namely, grasp stability, contact force distribution, and pull-out force. Finally, the experimental results obtained from a physical prototype of an underactuated linkage-driven gripper equipped with suction cups are illustrated, attesting to the feasibility and potential gain of the system.
Tactile sensing is essential for robotic manipulations and human‒machine interactions. It is vital to provide contact location and force information between the robotic gripper and objects for safe ...and effective operation. Many existing tactile sensors deploy an array of sensing units for pressure mapping and contact location recognition. However, it is still challenging to utilize such array sensors in robotic grippers for real-world applications due to the complex wiring and electronics, high cost, and l ow r eliability. I n t his w ork, w e p ropose a n on-array soft tactile sensor (NA-STS) that utilizes two triangle textile electrodes and a rectangle electrode to form a pair of soft capacitive pressure sensors in a differential configuration along its length. The sum of the two capacitance variations represents the amplitude of the force, whereas the difference between them represents the contact location. A three-layer electrode, shielded soft tactile sensor with dimensions of 12 mm × 60 mm was fabricated, characterized, and calibrated for simultaneous contact force and location measurement. The results show that the sensor can detect the force as low as 2.1mN, with a range over 25 N, and a maximum error of 2.5 mm for contact location detection. In addition, key design parameters of the NA-STS were investigated. Finally, two NA-STSs were integrated into a robotic gripper and demonstrated for monitoring the contact force and location during the gripping of various objects. The NA-STS has a simple structure, high performance, rapid response and is easy-to-implement, immune to proximity effect, and robust for real-word applications.
Web structure is a flexible structure widely used in animal predation behavior and human hunting work, which exhibits an excellent capability of gripping objects stably and securely. Inspired by the ...predation behavior of spiders, in this article, we present a bioinspired cobweb soft gripper, named WebGripper, which takes on a form like a spider web before grasping an object and presents an entangling state like a snake after grasping the object. These characteristics result in broad adaptability to various objects and enhanced grasping stability. The design concept, grasping principle, and fabrication process of the WebGripper are presented in this work, and the influences of cable layout and soft finger installation angle are analyzed to provide a reference for the design of the WebGripper. To evaluate the performance of the WebGripper, we carried out experiments on grasping objects with different shapes and sizes. Experimental results illustrated the universal adaptable grasping ability of the WebGripper, which exhibits excellent application prospects in many fields, such as goods sorting, fruit picking, and underwater fishing. This work is expected to promote the development of a high-performance soft gripper that may be used in a number of applications based on the understanding of the bionic web structure.
This article presents a new cable-driven underactuated robotic gripper, called TWISTER Hand. It is designed for adaptable grasping of objects in different shapes, weights, sizes, and textures. Each ...finger of the gripper is made of a compliant and continuum mechanism inspired by an origami design. This design is converted into a computer-aided design (CAD) model and 3-D printed using flexible and rigid polymer composite materials. Two CAD modeling methods for this design are compared in terms of structural stiffness and durability in the printed outcomes. For each design, two soft materials are used for preliminary evaluation of the material effect in these properties. The best combination of the model and material is selected to fabricate the three fingers of the robotic gripper. Each finger has a single cable routed along the structure. All three cables are tied and actuated simultaneously using a single servo motor to generate closing and opening motions in the gripper. TWISTER Hand's adaptable grasping capability is tested using 36 different objects. The robot's grasping performance under object pose uncertainties is also experimentally tested and analyzed. This compact fully integrated gripper can be attached to a robotic arm for various manipulative tasks.
Mobile sub‐millimeter micro‐robots have demonstrated untethered motion and transport of cargo in remote, confined or enclosed environments. However, limited by simple design and actuation, they lack ...remotely‐actuated on‐board mechanisms required to perform complex tasks such as object assembly. A flexible patterned magnetic material which allows internal actuation, resulting in a mobile micro‐gripper which is driven and actuated by magnetic fields, is introduced here. By remotely controlling the magnetization direction of each micro‐gripper arm, a gripping motion which can be combined with locomotion for precise transport, orientation, and programmable three‐dimensional assembly of micro‐parts in remote environments is demonstrated. This allows the creation of out‐of‐plane 3D structures and mechanisms made from several building blocks. Using multiple magnetic materials in each micro‐gripper, the addressable actuation of gripper teams for parallel, distributed operation is also demonstrated. These mobile micro‐grippers can potentially be applied to 3D assembly of heterogeneous meta‐materials, construction of medical devices inside the human body, the study of biological systems in micro‐fluidic channels, 3D micro‐device prototyping or desktop micro‐factories.
A robotic micro‐gripper is made from a flexible patterned magnetic composite material. By remotely controlling the magnetization direction of each micro‐gripper arm, grasping motion is combined with locomotion for precise transport, orientation, and programmable three‐dimensional assembly of micro‐parts in remote environments.
Despite good performance in grasping irregular fragile objects, soft grippers exhibiting low stiffness, and carrying capacity lack multidirectional grasping ability in the case of inclination. To ...address this problem, we propose a novel rigid and soft coupling variable stiffness module that employs a folded plate mechanism (FPM) to provide rigid multidirectional loading and combines it with particle jamming to achieve local variable stiffness with the characteristics of a finger grasping structure. Hence, a variable stiffness multidirectional soft grasping robot is developed to realize soft grasping and multidirectional rigid loading. The bending and stiffness control of the variable stiffness soft gripper is realized by a double-layer pneumatic driving structure with the advantages of simple control and corresponding speed. Moreover, good self-recovery is achieved with the soft outer layer since the particles can quickly return to the initial state due to partitioning of the FPM. Finally, prototype experiments verify its strong adaptability and stable multidirectional grasping ability, and experimental results show that the maximum grasping weight in each direction can be increased by more than three times with the variable stiffness.
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