Prototype Gripper Research Articles

Experimental investigation on adaptive grasping of a novel 3D-MSSPA gripper in complex space

Many achievements for soft grippers are made in the structure design and grasping of target objects. However, there are limited studies on grasping objects with different attributes by soft grippers with omnidirectional bending capabilities within environments containing obstacles. In this paper, drawing inspiration from the multi-segment structure of the biological finger, a 3D-multi-segment soft pneumatic actuator (3D-MSSPA) with a strong envelope and omnidirectional independent bending is designed and manufactured. Additionally, we developed a novel prototype for a soft gripper prototype. A quasi-static model is proposed to effectively describe the bending deformation of 3D-MSSPA. The experimental results show that, for an applied pressure of 40kPa, the single segment SPA achieves a maximum bending angle of 175.2°, aligning closely with the theoretical prediction. Furthermore, the omnidirectional bending ability of multi-segments is analyzed through the finite element method, and a position compensation method for gravity deviation is presented. Through experiments, the pressure fore and lifting force of the soft gripper are investigated, yielding maximum values of 11N and 4.08N, respectively. These results serve as a benchmark for the mass grasping range of the target objects. Finally, the experiments are conducted to demonstrate the soft gripper’s adaptive and flexible grasping capabilities for objects with varying attributes, in both free space and complex space with obstacles. These experiments showcase their ability to avoid obstacles, adaptively grasp objects, and their good envelope ability. The proposed 3D-MSSPA can provide good inspiration and reference for flexible applications, particularly in fields such as post-disaster rescue and rehabilitation medicine.

A low-cost underactuated compliant gripper with multifunctional jaws for precision manipulation

Precision manipulation tasks often require the use of compliant grippers to handle small and delicate objects accurately. This paper proposes a novel low-cost underactuated compliant gripper with integrated position and force sensors for precision manipulation. The gripper has a millimeter-scale grasping range and can adapt to objects of varying sizes and shapes. This is made possible by a flexure motion transmission mechanism that can undergo significant deformation, an underactuated seesaw flexure mechanism, and a pair of multifunctional jaws. Analytical models based on the pseudo-rigid-body approach are developed to analyze the kinematic, static, and dynamic characteristics of the gripper design. Finite element simulations are conducted to investigate the static and dynamic performance of the gripper. The gripper prototype is fabricated using 3D printing technology for a series of experimental tests. The results of these experiments demonstrate that the developed gripper has excellent motion tracking capabilities and high motion and force resolutions, enabling precise and accurate manipulation tasks. Furthermore, the gripper is capable of successfully grasping objects of different sizes and shapes through parallel and enveloping grasps.

A gripper for delicate edible manipulation

The general manipulation of delicate edible products requires of specific grippers able to firmly grasp these kind of products without damaging them. To address this problem we follow a soft and variable-stiffness approach. In this paper we design and construct successive gripper prototypes which fingers are composed of rigid and soft parts. The stiffness of the soft parts can be modified using the jamming principle. The gripper properties are experimentally evaluated using a subset of NIST benchmarks. This allows to obtain comparable and standardised results, used to improve the initial gripper design. In addition a new benchmark, the edible grasping benchmark, is proposed and used to measure the performance of the grippers while grasping fruits and vegetables. The final gripper prototype overcomes the problems observed in fruit and vegetable picking systems. It has been demonstrated in the experimental tests that the gripper has sufficient payload and adaptability to grasp several edibles without damage.

A Soft-Rigid Hybrid Gripper With Lateral Compliance and Dexterous In-Hand Manipulation

Soft grippers are receiving growing attention due to their compliance-based interactive safety and dexterity. Hybrid gripper with soft actuators enhanced by rigid constraints is receiving growing attention in soft gripper design. With rigid structural components actuated by soft actuators, they could achieve excellent grasping adaptability and payload while also being easy to model and control with conventional kinematics. However, existing works were mostly focused on achieving superior payload and perception with simple planar workspaces, resulting in far less dexterity compared with conventional grippers. In this work, we took inspiration from the human metacarpophalangeal (MCP) joint and proposed a new hybrid gripper design with eight independent muscles. It was shown that adding the MCP complexity was critical in enabling a range of novel features in the hybrid gripper, including in-hand manipulation, lateral passive compliance, as well as new control modes. A prototype gripper was fabricated and tested on our proprietary dual-arm robot platform with vision-guided grasping. With very lightweight pneumatic bellows soft actuators, the gripper could grasp objects over 20 times its weight with lateral compliance. Using the dual-arm platform, highly anthropomorphic dexterous manipulations were demonstrated using two hybrid grippers, from tug of war on a rigid rod to passing a soft towel between two grippers using in-hand manipulation. Matching the novel features and performance specifications of the proposed hybrid gripper, the underlying modeling, actuation, control, and experimental validation details were also presented, offering a promising approach to achieving enhanced dexterity, strength, and compliance in robotic grippers.

Permanent-Magnetically Amplified Robotic Gripper With Less Clamping Width Influence on Compensation Realized by a Stepless Width Adjustment Mechanism

Machines such as robotic grippers use powerful actuators or gearboxes to exert large loads at the expense of energy consumption, volume, and mass. We propose a stepless force amplification mechanism that assists clamping by a pair of permanent magnets, in which the external control force required to adjust their distance, and thus the output force, is suppressed by compensation springs. For further sophistication, we invented a new width adjuster using a lever. By separating the actuation of fingers and compensated magnets temporarily, the adjuster eliminated the nonlinear influence of the object width on the clamping force. The prototype gripper for proof of concept revealed that the adjuster successfully linearized the width-force characteristic with an inclination of 0.15 N/mm, which is sufficiently insignificant compared to the major output force of approximately 50 N. The force amplification effect coexisted with this phenomenon, such that the clamping force was amplified to 137.5% while maintaining the energy consumption of a DC motor, and the force-energy efficiency was multiplied by 1.39. Thus, able to be driven by a weaker, smaller, and lighter actuator, the gripper contributes to extension of the operation time of robots with limited power.

Enhancing the Tensile-Shaping Stability of Soft Elongation Actuators for Grasping Applications

Soft elongation actuators are widely applied in soft robotic grippers, providing a promising solution to adjust the grasping range. However, there are some limitations in keeping their tensile shaping stability under high payloads. This work presents a universal variable stiffness mechanism called Cross-Fibre to reduce the deformation and improve the load-bearing capacity of soft elongation actuators. The proposed mechanism is composed of two symmetrical fibre loops in an up-and-down crossed arrangement around the soft elongation actuator. The fibre media on both sides can be stretched compliantly with the actuator, and thus achieve global variable stiffness. In addition, based on the soft elongation actuator with variable stiffness, this work also develops a novel soft gripper prototype for automatically adjusting the grasping range and enhancing grasping applications. Experiments demonstrate that the soft elongation actuator with Cross-Fibre effect has strong tensile-shaping ability, and the soft gripper can stably grasp objects weighting more than 1700 g. Such efficient performance will promote various applications in daily life and industry.

A Novel Gripper Prototype for Helical Bird Diverter Manipulation

Energy grids represent a fundamental infrastructure of any country. These structures consist of many kilometres of power lines that must be periodically inspected and maintained. Among the necessary operations are installing and removing bird diverters to reduce bird strikes on power lines. These devices are intended to improve birds’ detection of power lines and reduce the risk of collision. Often, the installation and removal of bird diverters from power lines is accomplished by humans operating from helicopters or directly on the power lines. Apart from the considerable cost of these operations, working in elevated environments creates human safety risks. To reduce these risks, this paper proposes a novel solution to automatize these tasks. The proposed solution is a prototype gripper that can be mounted on unmanned aerial vehicles (UAVs) and remotely operated to install or remove bird diverters. This work presents a mechatronic device and software architecture system that is experimentally evaluated in a laboratory mock-up, which consists of a manipulator equipped with the proposed tool for removing a bird diverter. Future work is needed to deploy the proposed tool on a UAV.

Finite Element Analysis of a Novel Robotic Gripper:Grabo

Robotic grippers, with several design variations in its jaws, are gaining popularity in commercial market worldwide in recent past. In fact, these customized robotic grippers are widely used for diverse end-applications in various arenas. We have aimed to optimize the mechanical design of such customized robotic grippers having two fingers (jaws), as those grippers are the most prevalent variants in industrial robots. In this study, a niche contigutive robotic gripper for direct adhesion contactis developed, to meet the technical trials of force-closure of grasp. The prime focus of our research is reduction of the tareweight of the prototype gripper keeping its strength unaltered under the threshold of grasping maximum payload. Through Finite Element Analysis and optimization thereof, material retention percentage is defined for the prototype gripper so as to improve its overall envelope.

A Switched Adaptive Controller for Robotic Gripping of Novel Objects With Minimal Force

We present the design and implementation of an algorithm, equipped with a switched adaptive controller, for grasping unknown objects using a robot gripper. A Lyapunov-based analysis demonstrates that the switching controller is indeed asymptotically stable with both the translational and rotational slip velocities converging to the origin. Experimental results using a novel sensorized gripper prototype and objects of different sizes, shapes, and weights show that the proposed algorithm not only ensures the prevention of slippage of the grasped objects, but is also able to apply the minimal force needed to safely grasp these objects without causing excessive deformation.

A Novel Magnetic Transmission for Powerful Miniature Surgical Robots

Untethered magnetically actuated robots present significant advantages for biomedical applications by allowing power to be delivered wirelessly to remote, miniature robots through flesh and bone. Nevertheless, generating enough usable force to interact with their environment remains a challenge: Most millimeter-size magnetic robots achieve forces of much less than 0.1 N, which limits their medical applications. Therefore, a compact, millimeter-scale transmission is needed to amplify the output force. A novel microtransmission system is presented, composed of a driving magnet suspended between two twisted string actuators. An analytical model of the transmission is formulated to predict its behavior under both fixed load and fixed displacement configurations. Experimental measurements are used to validate the predicted maximum achievable force, to quantify the transmission performance over numerous cycles, to determine the effect of different string materials, and to determine the impact of hysteresis and viscoelasticity. Finally, the transmission is integrated into a 3 mm diameter surgical gripper prototype to demonstrate its effectiveness. With only a modest 20 mT of applied magnetic field, the gripper generates 1.09 N gripping force—a factor of 35 improvement in mechanical advantage and a factor of 62 improvement in gripping force compared to a similar size gripper using direct magnetic actuation. This microtransmission for miniature magnetic robots will enable high-strength untethered robots for minimally invasive surgical applications.

Novel design of a piezoelectrically actuated compliant microgripper with high area-usage efficiency

Microgrippers act as an end effector in micromanipulation systems, completing the pick-transport-release operations during the working process. This paper presents the design, modeling, optimization, simulation, and experiment of a novel piezoelectrically actuated compliant microgripper for micromanipulation and microassembly. Considering the space and cost constraints of the micromanipulation system, the area-usage efficiency and piezoelectric actuator utilization efficiency are introduced to evaluate its performance. A three-stage amplification mechanism based on bridge-type and leverage mechanisms arranged in series is introduced to achieve a large jaw displacement. The displacement amplification ratio of the microgripper is analyzed via the pseudo-rigid-body model approach. Optimization based on response surface analysis was conducted to determine the structural parameters of the compliant mechanism. Finite-element analysis is performed to evaluate the gripper performance. Moreover, a gripper prototype was fabricated for the experimental test. The investigation results indicate that the gripper allows a maximum gripping displacement of 548.42 μm, a first natural frequency of 334 Hz, and a motion resolution of ±0.75 μm. In comparison with previous designs, the reported microgripper has the advantages of a larger displacement, higher area-usage efficiency, and better PEA utilization efficiency. The micromanipulation capability of the developed gripper was demonstrated by gripping three tiny objects of different sizes and shapes.

Design and Testing of a New Piezoelectric-Actuated Symmetric Compliant Microgripper

Precise and stable operations in micromanipulation and microassembly require a high-performance microgripper. To improve the predominant static and dynamic characteristics, a novel piezoelectric-actuated compliant microgripper is designed, analyzed, and tested in this paper. The microgripper realizes a large gripping stroke by integrating a compliant bridge mechanism, an L-shaped mechanism, and a levered parallelogram mechanism. Optimization technology based on response surface analysis is applied to demonstrate the influence of structural parameters on the microgripper performance. Simulation results of finite element analysis reveal the superior performance of the designed microgripper in terms of gripping displacement, mechanism stiffness, equivalent stress, and natural frequency. A gripper prototype has been fabricated, and experimental studies have been conducted to test the microgripper’s physical properties. Experimental results show that the microgripper can grasp micro-objects with a maximum jaw motion stroke of 312.8 μm, natural frequency of 786 Hz, motion resolution of ±0.6 μm, and force resolution of ±1.69 mN. The gripping tests of an optical fiber with a diameter of 200 μm and a metal sheet with a thickness of 100 μm have been performed to demonstrate its gripping capability with position and force control.

A 3D-Printable Robotic Gripper Based on Thick Panel Origami.

Origami has been a source of inspiration for the design of robots because it can be easily produced using 2D materials and its motions can be well quantified. However, most applications to date have utilised origami patterns for thin sheet materials with a negligible thickness. If the thickness of the material cannot be neglected, commonly known as the thick panel origami, the creases need to be redesigned. One approach is to place creases either on top or bottom surfaces of a sheet of finite thickness. As a result, spherical linkages in the zero-thickness origami are replaced by spatial linkages in the thick panel one, leading to a reduction in the overall degrees of freedom (DOFs). For instance, a waterbomb pattern for a zero-thickness sheet shows multiple DOFs while its thick panel counterpart has only one DOF, which significantly reduces the complexity of motion control. In this article, we present a robotic gripper derived from a unit that is based on the thick panel six-crease waterbomb origami. Four such units complete the gripper. Kinematically, each unit is a plane-symmetric Bricard linkage, and the gripper can be modelled as an assembly of Bricard linkages, giving it single mobility. A gripper prototype was made using 3D printing technology, and its motion was controlled by a set of tendons tied to a single motor. Detailed kinematic modelling was done, and experiments were carried out to characterise the gripper’s behaviours. The positions of the tips on the gripper, the actuation force on tendons, and the grasping force generated on objects were analysed and measured. The experimental results matched well with the analytical ones, and the repeated tests demonstrate that the concept is viable. Furthermore, we observed that the gripper was also capable of grasping non-symmetrical objects, and such performance is discussed in detail in the paper.

Combining Sensors Information to Enhance Pneumatic Grippers Performance.

The gripper is the far end of a robotic arm. It is responsible for the contacts between the robot itself and all the items present in a work space, or even in a social space. Therefore, to provide grippers with intelligent behaviors is fundamental, especially when the robot has to interact with human beings. As shown in this article, we built an instrumented pneumatic gripper prototype that relies on different sensors’ information. Thanks to such information, the gripper prototype was able to detect the position of a given object in order to grasp it, to safely keep it between its fingers and to avoid slipping in the case of any object movement, even very small. The gripper performance was evaluated by means of a generic grasping algorithm for robotic grippers, implemented in the form of a state machine. Several slip tests were carried out on the pneumatic gripper, which showed a very fast response time and high reliability. Objects of various size, shape and hardness were employed to reproduce different grasping scenarios. We demonstrate that, through the use of force, torque, center of pressure and proximity information, the behavior of the developed pneumatic gripper prototype outperforms the one of the traditional pneumatic gripping devices.

Design and prototyping of a novel gripper using PVC gel soft actuators

Soft grippers take an important role in picking up and manipulating objects for adaptive machines and facilities to achieve near-human operations. The technology of soft actuators should be one of the key issues for developing such grippers. In this study, we proposed a novel two-figure gripper using polyvinyl chloride (PVC) gel-based multilayered soft actuators. We used the contraction-expansion movement and generation force of the actuators to realize the gripper movement. A prototype gripper and a testing platform were designed, fabricated and the basic characteristics were evaluated for the pilot study. And a preliminary clamping experiment was conducted to verify the reasonability of the proposed gripper. The results show that the gripper can steadily grasp various small, lightweight, fragile, and irregular objects which demonstrated the feasibility of the practical use of the gripper.

Design and analysis of a variable-stiffness robotic gripper

This paper presents the design and analysis of a novel variable-stiffness robotic gripper, the RobInLab VS gripper. The purpose is to have a gripper that is strong and reliable as rigid grippers but adaptable as soft grippers. This is achieved by designing modular fingers that combine a jamming material core with an external structure, made with rigid and flexible materials. This allows the finger to softly adapt to object shapes when the capsule is not active, but becomes rigid when air suction is applied. A three-finger gripper prototype was built using this approach. Its validity and performance are evaluated using five experimental benchmark tests implemented exclusively to measure variable-stiffness grippers. To complete the analysis, our gripper is compared with an alternative gripper built by following a relevant state-of-the-art design. Our results suggest that our solution significantly outperforms previous approaches using similar variable stiffness designs, with a significantly higher grasping force, combining a good shape adaptability with a simpler and more robust design.

Estimation of Dynamic Characteristics of a Novel Non-Parallel Detachable-Jaw Robotic Gripper Using Finite Element Method

Robotic grippers are increasingly aiming towards versatility to suit industrial applications of modern times. Detachable-type jaws of the robotic grippers do play a significant role in diverse end-uses in real-time. A novel contigutive robotic gripper was used in the present study for direct adhesion contact to meet the technical challenges of force-closure of the grasp. The crux of the design was realized through an iterative optimization so as to ensure mismatch of natural frequency of the gripper and the forcing frequency in order to avoid resonance condition. Natural frequencies and mode shapes of the prototype gripper system were studied in order to understand its dynamic behaviour. Two commercial Finite Element Analysis Software were used for the effective characterization of the real-time dynamics of the gripper system. The dynamic analysis and simulation were instrumental in manufacturing of the test-pieces and final prototype of our indigenous robotic gripper.

Gamma‐Ray Tolerant Flexible Pressure–Temperature Sensor for Nuclear Radiation Environment

AbstractReliable and highly sensitive flexible physical sensors hold great potential for applications in emerging technologies. Among others, of particular importance is to embed the sensor into operations at the hazardous fields, like radioactive zones or nuclear power plants. However, a significant challenge is to develop the radiation tolerant flexible sensors with stable performance under extreme conditions. This study presents a flexible pressure–temperature sensor based on MXene/Fe3O4/graphene porous network/Ecoflex (MFGPNE) and thoroughly investigates the effect of a high dose of γ‐irradiation on their physical and electrical properties. The proposed sensors are characterized by a 4.71 kPa−1 sensitivity to the applied pressure in the range of 0–62.5 kPa and by a 2.23% resistance change per degree in the temperature range of 21–110 °C. The in situ electrical experiments, performed during irradiation of the MFGPNE sensor by 20 kGy of γ‐rays (60Co), reveal the stable and reliable operation of the sensor. Superior radiation stability and pressure–temperature sensitivity are achieved due to the inherent nature of the materials and the sophisticated design of the proposed sensors. Moreover, an MFGPNE sensor‐based prototype gripper for grasping force control by remote monitoring of the press and lift forces demonstrates the application of the proposed sensor.

A Microgripper With a Large Magnification Ratio and High Structural Stiffness Based on a Flexure-Enabled Mechanism

This article presents a piezoelectric-actuated microgripper that mainly consists of a three-stage flexure-based amplification mechanism to achieve a large magnification ratio with an excellent linearity, a large operating bandwidth, and a great force output capacity for micromanipulation and assembly. The first two stages are configured as two bridge-type parallelogram amplification mechanisms connected in serial to provide advantages in terms of high structural stiffness and compactness. This configuration is capable of generating large forces to maintain the following connection leverage mechanism and ensure a large displacement output, and also produces a stable amplification ratio insensitive to the input change. The finite element method-based simulation has been performed to investigate both static and dynamic characteristics of the designed microgripper. Simulation-enabled structural optimization design has been implemented to further aid and improve the proposed design. The simulation results indicate that the amplification ratio reaches 30.3 with a maximum clamping force of up to 2.17N. The gripper prototype has been fabricated based on the wire electrodischarge machining technique, and its performances have been validated through pick-and-place of microbeads experiments and dynamic tests. The experimental results have demonstrated the large amplification ratio of 31.88 with excellent linearity, and the motion stroke of 218 μm with a large grasping force up to 1993 mN. They well match the results from both simulation and theoretical calculation in terms of motion range and amplification ratio.

A Bioinspired Soft Swallowing Gripper for Universal Adaptable Grasping.

This article presents the design, fabrication, modeling, and preliminary tests of a bloodworm-inspired soft gripper for universal grasping. The gripper was designed and fabricated based on a toy called water snake wiggly (WSW). The toroidal WSW can evert itself inside-out or outside-in, just like a bloodworm everting its teeth outside to hunt and inside to feed. By driving a WSW rolling itself outside-in to wrap around the items, a bloodworm-inspired gripper was achieved with a flexible and passive form-fitting grasp. To enhance the capability of the gripper, two alternative detachable modules were added to the gripper-a vacuum suction cup for handling objects with smooth nonporous surfaces and an end-needle for taking in and expelling noncorrosive liquids like a syringe. We analyzed the working principles of the gripper and derived the relationship between the gripper's holding force and the objects' scale. Preliminary experiments with a motor-driven gripper prototype were conducted to verify its performance. The experimental results conform well with our theoretical analysis and also indicate the gripper's good universal grasping capacity and reliability in handling a wide range of objects with different surface shapes, geometric dimensions, and stiffness. In addition, the gripper has the unique abilities to pick more than one object during a maneuver, grasp multiple objects in a row without releasing the former ones, and even grasp powdered objects. These have presented a challenge for the existing robotic grippers.