This article presents an innovative, motor-driven, three-finger compliant gripper for adaptive grasping of size-varied delicate objects. An optimized compliant finger design is identified numerically ...through a topology optimization method. A stepper motor is used to actuate three identical compliant fingers, which can operate through elastic bending deformation. Finite-element models are developed to investigate the maximum equivalent stress, input force, and output displacement relations corresponding to the amount of input displacement of the compliant finger. Simulation results show that the proposed finger design is with a lower driving force and a lower maximum equivalent stress during operation comparing to one previous design. The proposed compliant finger is prototyped by three-dimensional printing using thermoplastic elastomer. Experimental results for the input displacement versus input force and input displacement versus geometric advantage relationships of the prototyped finger agree well with simulation results. The developed three-finger soft robotic gripper is mounted on an industrial robot arm to demonstrate its capability in handing size-varied delicate objects, such as egg, fruits, and glass products. Experimental results show that the proposed three-finger gripper can be used to grip object with a maximum weight of 4.2 kg and a maximum object size of 140 mm. The overall weight of the developed three-finger soft robotic gripper is 1.2 kg. The load capacity of the developed gripper can vary according to the friction between gripper and object. The maximum payload of the gripper can be increased to 9.5 kg when an additional antislip foam tape is applied on the grip surfaces of the compliant fingers.
This paper proposes a new compliant gripper with integrated position and force sensors dedicated to automated microassembly tasks. The uniqueness of the gripper is that it possesses a large gripping ...range with a bidirectional drive, and it is capable of detecting grasping force and environmental interaction forces in horizonal and vertical axes, respectively. This is enabled by a mechanism design based on a rotary flexure bearing. Moreover, a compliant mechanism with two-stage stiffness is designed to provide the force sensing with dual sensitivities and measuring ranges to accommodate the grasp of objects with different sizes and weights. Analytical models are derived to predict the grasping range, force sensing sensitivities, and ranges. These models are verified by conducting finite-element analysis simulations. A proof-of-concept prototype gripper is developed for experimental calibration and performance testing. Results reveal that the single set of strain-gauge force sensor is able to detect both grasping and interaction forces in an alternate manner. The dual-sensitivity, dual-range force sensor provides a solution to large-range gripper with finer and coarser force sensing in a small and large ranges, respectively .
This article investigates some aspects related to the design, modeling, prototyping, and testing of soft–rigid tendon-driven grippers. As a case study, we present the design and development of a ...two-finger soft gripper and exploit it as an example to demonstrate the application scenario of our mathematical model based on screw theory. A mathematical formulation based on screw theory is then presented to model gripper dynamics. The proposed formulation is the extension of a model previously introduced including the mechanical system dynamics. In this type of gripper, it is possible to achieve different behaviors, e.g., different fingertip trajectories, equivalent fingertip stiffness ellipsoids, etc., while keeping the same kinematic structure of the gripper and varying the properties of its passive deformable joints. These properties can be varied in the prototype by properly regulating some manufacturing parameters, such as percentage of printing infill density in a 3D printing process. We performed experiments with the prototype of the gripper and an optical tracking system to validate the proposed mathematical formulation, and to compare its results with other simplified formulations. We furthermore identified the main performance of the gripper in terms of payload and maximum horizontal resisted force, and verified the capabilities of the gripper to grasp objects with different shapes and weights.
In this study, we built a four-fingered soft robotic gripper with tunable effective finger lengths. This robotic model is purely made of soft materials and allows two working modes that require very ...simple control: 1) deflate the soft fingers for bending to one direction therefore to open the gripper "claw" and 2) inflate the fingers with compressed air for bending to the reverse direction, therefore to grip objects reversibly. Systematic tests of the gripping performance of the soft robotic model were conducted for 5 effective finger lengths ranging from 30 mm to 100 mm. Under each effective length, we measured the pull-off force of 8 sphere-shaped objects with diameters from 20 to 90mm, and five typical geometric shaped objects including sphere, cubic and cylinder etc. We also measured the pull-off force of gripping objects with different stiffness. Notably, we found that each object with different size prefer a "sweet" effective finger length for generating maximum pull-off force. We show that tunable effective finger length for the soft robot can significantly improve the performance when gripping multiple objects. Current soft robotic prototype exhibits a simple-control, low-cost approach of grasping objects with different size, weight, and shape as well as material stiffness, and may open up new avenues for future industrial gripping.
Soft actuators typically exhibit low stiffness and low load-bearing properties due to the intrinsic limitations of soft materials. Stiffness modulation is an effective means to improve the ...performance of soft actuators. However, most stiffness-tunable mechanisms are nonstretchable, and have difficulty in independently adjusting the tensile stiffness of soft elongation actuators. Here, a universal cross-fiber jamming mechanism with both elongation and bending stiffness-tunable capability is proposed for soft bellows actuators. It is composed of two semicircular symmetrical fiber bundles in an up-and-down crossed arrangement, and can follow the tensile state of the soft bellows actuator through the passive staggered motion of the layered fiber bundles. Furthermore, a soft gripper with wide grasping range and sufficient grasping stability is also developed by applying soft bellows actuators with cross-fiber jamming mechanisms. Experiments are conducted to show the related performance of the proposed cross-fiber jamming mechanism. The results show that it has fast antiimpact damping response, strong shaping ability and adjustable stiffness. Such efficient performance will promote the ability of grasping robots, and is expected to be used in daily life and industry.
To enhance the tactile perception and human-computer interaction efficiency of soft robots, an intelligent soft gripper system is proposed in this study. The system utilizes triboelectric ...nanogenerator sensors to capture tactile information during the grasping process. By employing a patterned electrode design, the sensor can extract multiple data, including the contact material, contact position, contact area, and slip. The conducted experiments revealed that the use of conductive gel instead of conventional metal electrodes improves compatibility with the soft gripper. The collected information is used to train the support vector machine (SVM) model, achieving accurate recognition of various objects with a recognition accuracy of 98.5%. Real-time communication analysis using the developed model demonstrates the recognition ability of the system when the software gripper interacts with objects, highlighting its application potential in human-computer interaction.
This work introduces TRIGGER, the first lighTweight univeRsal jammInG Gripper for aErial gRasping. TRIGGER is an omnidirectional, landing-capable aerial grasping system with resilience and robustness ...to collisions and inherent passive compliance. In particular, this work presents the design, fabrication, and experimental validation of a novel, intelligent, modular, universal jamming gripper specifically designed for aerial applications. Leveraging recent developments in particle jamming and soft granular materials, TRIGGER generates 15 N of holding force with only a relatively small activation force of 2.5 N. Experiments show the relationship between fill ratio and activation force and reveal that adding an additive to the membrane's silicone mixture improves the holding force by up to 52 %. Based on the experimental data, a simulation model for robotic simulators is introduced to facilitate future controller developments. To showcase the concept, TRIGGER is attached to a multicopter platform, performing a pick-and-place task under laboratory conditions. The aerial experiments are concluded by grasping a variety of shapes demonstrating the universal grasping capability.
Measuring and controlling the force required to grip a nerve is required to avoid any undesired neurological damage caused by an excessive suction force applied to the tissue. We aimed to develop a ...suction-based nerve gripper that can measure the suction force applied to the gripped peripheral nerve. A tiny force sensor can be incorporated by casting a soft material on a barometric pressure sensor chip and embedding it in the suction tip. In this study, a suction tip was designed based on a parametric analysis. The sensing characteristics and performance were evaluated experimentally. The experimental results demonstrate that a suction tip exhibits a force measurement capacity of approximately 2.8 N with a controlled suction force at 0.1 N intervals. The practical applicability of the proposed gripper was assessed based on an in vivo experiment performed on small animal subjects.
With the recent introduction of ambitious industrial strategies such as Horizon 2020 and Industry 4.0, a massive focus has been placed on the development of an efficient robotic workforce. Amongst ...all the operations robotic systems can take care of, handling remains a preferred choice due to a combination of factors including its often repetitive nature and low skill requirement. The associated demand for grasping tools has led to an ever increasing market for manipulation end-of-arm tooling from which a handful of industry giants have emerged. Based on data publicly accessible from the catalogs of several well-known companies, this paper aims at presenting a review on the characteristics of pneumatic, parallel, two-finger, industrial grippers. Included in the specifications under scrutiny in this paper are: stroke, force, weight, as well as a performance index referred to as the C-factor. This last index is a combination of three of the aforementioned characteristics and has been proposed in the literature as a measure of the efficiency that a gripper is capable of reaching. As will be shown, by analyzing hundreds of specifications it appears that, indeed, the range of C-factors of the grippers built by one company can be often consistently different from these of competitors. Furthermore, an important bias for certain typical specifications can be observed in most of the grippers which seems at odd with the requirement of modern robotic systems. This latter remark will open up a closing discussion proposed in the last part of this paper on the future evolution of grippers based on emerging new products.
This article develops a mechanical screwing tool and its manipulation policies for two-finger parallel robotic grippers. The tool is based on a combined scissor-like element (SLE) and double-ratchet ...mechanism that converts the gripping motion of two-finger parallel grippers into a continuous rotation to realize tasks like fastening screws. The tool is entirely mechanical. There is no need for external cable connections. The manuscript includes two parts. For one thing, it shows the details of the tool design, optimizes the tool's dimensions and effective stroke lengths, and studies the contacts and forces to achieve stable grasping and screwing. For another, it presents the related manipulation and control policies, including recognizing the tool, changing tool poses, and completing screw fastening tasks. The designed tool, together with the related manipulation and control policies, are analyzed and verified in several real-world applications. The results show that the tool has satisfying mechanical properties. Robots with parallel grippers can robustly and flexibly use the tool to fasten screws. The tool can also be used collaboratively with other tools to finish difficult tasks. In the future, similar tools are expected to replace special-purpose end-effectors or tool changers for more flexible robot integration.
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