Soft Pneumatic Gripper Research Articles

Printing of Tactile Sensors Upon the Surface of Pneumatic Soft Gripper by Direct Writing and Electrospraying to Enable Intelligent Grasping

Soft grippers with sensory‐integration mimicking humanoid hands, capable of grabbing various kinds of objects in a safe and easy manner, have numerous potential applications in advanced areas. However, precise sensing capabilities of the soft grippers for external stimuli are still nascent and fabrication of integrating sensory receptors remains a challenge. Herein, multiple tactile (pressure, temperature, and humidity) sensors are fabricated on the surface of pneumatic soft fingers by printing technologies including direct writing and electrospraying to simultaneously detect external stimuli while grasping. Composites composed of graphene nano‐platelets (GNPs)/multi‐walled carbon nanotube (MWCNT)/polyethylene oxide (PEO), reduced graphene oxide (rGO), and graphene oxide (GO) are selected as sensitive materials for pressure, temperature, and humidity sensor, respectively. The fingers are able to bend with an angle of 75° and output force of 0.133 N under air pressure of 12 kPa. The printed tactile sensors exhibit good sensing performance. The application of grasping a lemon, a cooked egg, and a plum demonstrates that the pneumatic soft gripper owns the capability of accurately detecting tactile changes during grasping different objects. Thus, such integration methods by direct writing and electrospraying will open a facile technical platform for constructing the soft grippers with tactile sensors.

Design and Manufacture of a Flexible Pneumatic Soft Gripper

The soft robot has many degrees of freedom, strong environmental adaptability, and good human–computer interaction ability. As the end-effector of the soft robot, the soft gripper can grasp objects of different shapes without destructivity. Based on the theoretical analysis of the soft robot, the kinematics model of the flexible gripper and the theoretical model of the bending deformation of the air cavity were established. Accordingly, the relationship between the bending angle of the soft gripper and the air pressure was determined. Through the application of finite element software, the bending degree of the pneumatic network multi-cavity soft gripper was simulated, and the influence of structural parameters of soft actuator on bending deformation was determined. In addition, the 3D technology conducts the printing of soft gripper fixtures and molds, the injection molds the actuator, and the human–computer interaction interface controls the movement of the gripper. This paper proposes the control and monitoring of the soft gripper are realized through the electrical control module, the air circuit control module, and the sensor group module, and the size of the airflow velocity can be controlled by PWM DC speed regulation. The adaptability of the soft gripper in grasping objects was verified. The results shows that the software gripper possesses good flexibility and can better grasp objects of different shapes.

Deformation Modeling and Simulation of a Novel Bionic Software Robotics Gripping Terminal Driven by Negative Pressure Based on Classical Differential Algorithm.

A general pneumatic soft gripper is proposed in this paper. Combined with the torque balance theory, the mathematical theoretical model of bending deformation of soft gripper is established based on Yeoh constitutive model and classical differential geometry. Assuming that the pressure in each inner cavity is evenly distributed, the input gas is in an ideal state, which is approximately treated as an isothermal condition, and all orifices experience blocked flow. In addition, compared with the mechanical work of gas, the energy related to gas flow and heat transfer is negligible. The nonlinear mechanical properties of silicone rubber are studied. It is regarded as isotropic and incompressible material, which is characterized by strain energy per unit volume. The material constant coefficients C10 and C20 are determined through the uniaxial tensile test, and the software gripper is simulated on the ABAQUS platform. The bending deformation models of grippers with three different force-bearing cavity structures are analyzed and compared, and the software clamping structure with the bending deformation most in line with the application conditions is selected. The limit input air pressure of the gripper and the situation of enveloping the clamping target object are analyzed. Through the bending deformation experiment, the maximum deformation angle is 72.4°. The relative error between the simulation analysis data and the prediction results of the mathematical model is no more than 3.5%, which verifies the effectiveness of the simulation and the correctness of the mathematical theoretical model of bending deformation. The soft manipulator proposed in this paper has good adaptability to grasping objects of different shapes and sizes. The minimum diameter of the target object that can be clamped is 0.1 mm. It can clamp the object weighing up to 1 kg. It has compact size, light weight, high ductility, and flexibility.

Mechanical performance analysis and experimental study of soft-bodied bird-billed pneumatic gripper

PurposeFlexible mechanical gripper has better safety and adaptability than a rigid mechanical hand. At present, there are few soft grippers for small objects on a millimeter scale. Therefore, the purpose of this paper is to design a soft pneumatic gripper for grasping millimeter-scale small and fragile objects such as jewelry and electronic components.Design/methodology/approachBy simulating the clamping action of the bird’s mouth and combining the high flexibility of the soft material, the bird’s beak soft pneumatic gripper is designed. First, the internal cavity of the gripping end of the gripper is determined by bending deformation calculation, and the brief manufacturing process of the gripper is outlined. Then, the single finger of the soft gripper is modeled mechanically, and the relationship between air pressure and bending deformation of the single finger is obtained. Finally, the experimental platform of the soft mechanical gripper is built, and the gripping performance of silicone rubber material is tested by comparison test, bending deformation test, stability test, adaptability test and gripping accuracy test.FindingsThe designed gripper has the advantages of simple structure, convenient operation, easy grasping of different small objects of millimeter-scale and good adaptability. It can grasp the precise dispensing needle with a minimum diameter of 0.19 mm, and its accuracy meets daily use.Originality/valueA new type of soft pneumatic, the mechanical gripper is proposed and manufactured. According to the shape of the bird’s beak and the calculation of bending performance, a hollow finger gripper with better bending performance is designed. Various test results show that the gripper has a significant clamping effect on millimeter small objects, which supplements the research field of millimeter small object gripper.

A Pneumatic Novel Combined Soft Robotic Gripper with High Load Capacity and Large Grasping Range

Pneumatic soft grippers have been widely studied. However, the structures and material properties of existing pneumatic soft grippers limit their load capacity and manipulation range. In this article, inspired by sea lampreys, we present a pneumatic novel combined soft gripper to achieve a high load capacity and a large grasping range. This soft gripper consists of a cylindrical soft actuator and a detachable sucker. Three internal air chambers of the cylindrical soft actuator are inflated, which enables them to hold objects. Under vacuum pressure, the cylindrical soft actuator and the detachable sucker can both adsorb objects. A finite element model was constructed to simulate three inflation chambers for predicting the grasping range of the cylindrical soft actuator. The validity of the finite element model was established by an experiment. The mechanism of holding force and adsorption force were analyzed. Several groups of experiments were conducted to determine adsorption range, holding force, and adsorption force. In addition, practical applications further indicated that the novel combined soft gripper has a high load capacity (10.85 kg) at a low pressure (16 kPa) and a large grasping range (minimum diameter of the object: d = 6 mm), being able to lift a variety of objects with different weights, material properties, and shapes.

A Multi-Curvature, Variable Stiffness Soft Gripper for Enhanced Grasping Operations

For soft grippers to be applied in atypical industrial environments, they must conform to an object’s exterior shape and momentarily change their stiffness. However, many of the existing grippers have limitations with respect to these functions: they grasp an object with only a single curvature and a fixed stiffness. Consequently, those constraints limit the stability of grasping and the applications. This paper introduces a new multicurvature, variable-stiffness soft gripper. Inspired by the human phalanx and combining the phalanx structure and particle jamming, this work guarantees the required grasping functions. Unlike the existing soft pneumatic grippers with one curvature and one stiffness, this work tries to divide the pressurized actuating region into three parts to generate multiple curvatures for a gripper finger, enabling the gripper to increase its degrees of freedom. Furthermore, to prevent stiffness loss at an unpressurized segment, this work combines divided actuation and the variable-stiffness capability, which guarantee successful grasping actions. In summary, this gripper generates multiple grasping curvatures with the proper stiffness, enhancing its dexterity. This work introduces the new soft gripper’s design, analytical modeling, and fabrication method and verifies the analytic model by comparing it with FEM simulations and experimental results.

Highly Stretchable Strain Sensor With Spiral Fiber for Curvature Sensing of a Soft Pneumatic Gripper

This paper proposes a flexible strain sensor based on the principle of resistance sensing to estimate the curvature information of the soft pneumatic gripper. The proposed sensor mainly includes a spiral conductive fiber and a central elastic base pillar. The conductive fiber is made of the stretchable elastomer DragonSkin-30 and multi-walled carbon nanotubes (MWCNTs) mixture, and a customized platform is designed to perform extrusion for fabrication. Three essential factors of the substrate, the fiber diameter, and the mixing ratio of MWCNTs have been investigated to improve the sensitivity and strain range of the sensor. Ecoflex-10 with excellent tensile properties has been selected to make the elastic base pillar. The stretchability, linearity, and service life of the sensor were improved by optimizing the spiral arrangement of conductive fibers through experiments. The proposed approach for manufacturing and assembly offers the advantages of easy implementation, convenient integration, and low cost. The electrical performances of the prototyped spiral sensor have been characterized, and it can reach an excellent strain range of up to 400% with linearity of 98%. The prototype has been integrated on the outer surface of a soft pneumatic gripper and well reflected the diameters of the unknown objects with an error of 3.99% through calibration and grasp-release experiments.

Three-Fingered Soft Pneumatic Gripper Integrating Joint-Tuning Capability

Compared with traditional rigid grippers, soft grippers are made of lightweight and soft materials and have the characteristics of flexible contact and strong adaptability, which are widely utilized to grasp fragile objects with complex contours and shapes. In this article, we design and fabricate a three-fingered stiffness-tunable soft gripper by integrating the joint-tuning capability. The soft fingers are composed of an internal bending actuator and an external fiber-jamming jacket, under an actuation of pneumatic pressure. Static and kinematic models are established to detect the bending angle and end trajectory of the internal bending actuator. Meanwhile, the bending angle and blocking force of bending actuator are experimentally measured and are comparably analyzed with the theoretical predictions. Jamming pressure is applied in the stiffness-tunable jacket to explore the variable stiffness and load-carrying capability of the soft finger. By incorporating the stiffness-tunable property, the grasping performance of various weights and types of goods, as well as the maximum grasping force of the soft gripper, is investigated. Finally, by patterning the stiffness-tunable jacket on the bending actuator, the variable curvature bending deformation and joint-tuning capability of the soft finger are achieved. This proposed soft gripper holds great potential applications in soft robotics community.

Proprioceptive Soft Pneumatic Gripper for Extreme Environments Using Hybrid Optical Fibers

Soft pneumatic robotic grippers can be used to conduct a wide range of tasks in extreme environments as they are generally free of conductive or magnetic components. But the sensorization of these grippers can potentially make them unsuitable for such environments and lower their performance through the introduction of electronic components or conductive materials into their structure. This work introduces the design of a sensorized soft pneumatic gripper using hybrid optical fibers making use of rigid and hard segments to measure the bending deformation and the contact force at specific segments of the finger. Using rigid optical fibers, which has low optical loss, for optical signal transmission allows to place all electronic components outside and away from the gripper ensuring the structure of the gripper and its nearby components are non-conductive and non-magnetic. The utilization of rigid reinforcements on the soft pneumatic actuator also helps maintain the performance of the actuator close to existing non-sensorized soft pneumatic actuators. This sensorized actuator is then used in a proprioceptive soft robotic gripper capable of controlling its grasping force.

Liquid Metal‐Enabled Soft Logic Devices

The controllable manipulation of gallium‐based liquid metal (LM) droplet presents a promising option toward the goal of making fully soft machines, which features an autonomy via external administration apparatus. While most current endeavors mainly concentrate on LM‐assisted actuations for soft robots, it is noteworthy that the peculiar behavior and LM droplet circuits thus enabled can be adopted as intelligent elements. Such characteristics will pave a way to innovate conventional logic devices and emancipate soft robots from the existing rigid machinery. Herein, LM‐based soft logic systems are described which are capable of regulating soft machines on macroscale. The core element is a LM‐based switch (LMS) with two specific types, both utilizing the LM droplet as a conducting medium. Soft logic gates of AND, OR, NOT, NAND, and NOR thus fabricated are demonstrated to generate electrical outputs as an integration of random inputs, and these signals can be adapted for electronic devices. For practical illustration, a logic accumulator is further constructed which can effectively regulate a pneumatic soft gripper within four states of inflation. The present LM‐enabled logic devices are expected to offer a feasible strategy to manipulate future soft machines without the participation of traditional rigid controlling elements.

Soft pneumatic gripper integrated with multi‐configuration and variable‐stiffness functionality

Soft grippers are compliant and self-adaptive, and can be highly compatible with the surrounding environment in grasping tasks. Currently, most soft pneumatic grippers are developed with a single grasping configuration, which leads to poor universality for different objects. Additionally, the oscillation caused by actuator's elastic bodies will result in poor stability during grasping and transportation, which can be improved by stiffness enhancement. A four-fingered soft pneumatic gripper is proposed by integrating multi-configuration and variable-stiffness functionality. The multi-configuration was realised by using the motion characteristics of a tangent mechanism. Meanwhile, a damping method based on electrorheological fluids was applied on a pneumatic actuator to improve the grasping stability. Besides, a machine vision technique was adopted to automatically adjust the grasping posture during manipulation. As a result, the proposed multi-configuration gripper can self-adaptively grasp different shapes of objects, especially two classical types, a pen canister as the flat cylinder and a cuboid box as the long cylinder. In addition, the electrorheological variable-stiffness method was manifested to be applicable for reducing pneumatic finger vibration. This research is expected to improve the versatility and grasping stability of soft pneumatic grippers.

A paper fortune teller-inspired reconfigurable soft pneumatic gripper

Soft pneumatic grippers (SPGs) have shown great grasping performances for various objects due to their simplicity, adaptability and rapid response. However, there are few SPGs that can grasp both flat and non-planar targets robustly. A reconfigurable mechanism that can transform the gripper into different states for grasping varied objects is desired by such versatile SPGs. Paper fortune teller (PFT) is a distinctive origami with 2D/3D shape switchability and 3D shape reconfigurability. In this paper, we propose a novel reconfigurable SPG which is inspired from PFT and augmented with an indirect vacuum adhesion (IVA) mechanism. The resultant gripper can not only lift flat-surface objects such as a piece of square glass (278 g) with the IVA force in its pad shape, but also pick up non-planar objects such as an orange (151 g) in a traditional grasping way in its four-converging-fingered shape. The experimental results reveal that our gripper can produce a maximum IVA force of about 4.24 N on acrylic plates and a maximum pulling force of about 2.10 N on 3D-printed non-planar objects respectively. The gripper’s traditional grasping robustness is also demonstrated when non-planar objects are placed irregularly (allowing up to 55 mm multi-orientation offsets or 20° multi-orientation drift angles). This new SPG design realizes the multi-function nature of origami transformation and is expected to promote the application of origami and soft gripper technologies.

Conformal Geometry and Multimaterial Additive Manufacturing through Freeform Transformation of Building Layers.

3D printing, formally known as additive manufacturing, creates complex geometries via layer-by-layer addition of materials. While 3D printing has been historically perceived as the static addition of build layers, 3D printing is now considered as a dynamic assembly process. In this context, here a new 3D printing process is reported that executes full degree-of-freedom (DOF) transformation (translating, rotating, and scaling) of each individual building layer while utilizing continuous fabrication techniques. Transforming individual building layers within the sequential layered manufacturing process enables dynamic transformation of the 3D printed parts on-the-fly, eliminating the time-consuming redesign steps. Preserving the locality of the transformation to each layer further enables the discrete conformal transformation, allowing objects such as vascular scaffolds to be optimally fabricated to properly fit within specific patient anatomy obtained from the magnetic resonance imaging (MRI) measurements. Finally, exploiting the freedom to control the orientation of each individual building layer, multimaterials, multiaxis 3D printing capability are further established for integrating functional modules made of dissimilar materials in 3D printed devices. This final capability is demonstrated through 3D printing a soft pneumatic gripper via heterogenous integration of rigid base and soft actuating limbs.

An untethered soft robotic gripper with high payload-to-weight ratio

Most of the soft grippers with high payload cannot carry cumbersome control systems and power sources themselves, and have to be tethered to external hardware through tubes and wires. To tackle this problem, we proposed an untethered soft pneumatic gripper with a high payload by developing a soft gripping structure with a high gripping force to pressure ratio. The untethered soft gripper integrates silicone elastomer structure, pneumatic artificial muscle (PAM), air pump, battery, controller, solenoid valve, and other components, with a total weight of 1.5 kg. The entire power sources of the untethered soft gripper are supplied by a battery, allowing it to perform at least 300 opening and closing movements. The lightweight and high load capacity of the untethered soft gripper enable its payload to weight ratio to exceed 26. Further, the untethered soft gripper can be installed on an unmanned aerial vehicle to expand its workspace. Also, a tightening force model for winding PAMs is presented in this paper, which can be used to evaluate the pressing force of the untethered soft gripper on the surface of an object.

Variable stiffness soft pneumatic grippers augmented with active vacuum adhesion

Soft pneumatic grippers (SPGs), made of highly stretchable elastomer materials with internal fluidic channels, are a popular soft robotic gripping technology, and have been configured as soft bending fingers for passively compliant grasping applications. It is challenging, however, for current SPGs to grip both flat, concave, and convex surfaces. Controllable adhesion augmented SPGs are promising solutions. We aim to develop a composite gripper structure that could enable SPGs with the capability to lift flat, concave, and convex surfaces using pneumatic inputs only. To this end, we present PneuIVAVS, a layer-jamming induced active vacuum adhesion (VA) augmented and variable stiffness (VS) fiber-reinforced SPG. This integrated PneuIVAVS design has enabled the gripper to generate a VA force without the requirement that all suction units should work. Also, a VA force analytical model and a shape-locking model of the PneuIVAVS design were developed and experimentally validated. In addition, the PneuIVAVS gripper presented good performance on gripping both flat, concave and convex objects with a range of contacting areas. According to the load capacity test, the gripper could grasp a maximum of approximately 470 g, 683 g, and 268 g when handling flat, concave, and convex surfaces respectively. Besides, the gripper could grasp curved surfaces with a minimum radius of curvature between 30 and 40 mm. The PneuIVAVS concept, design, and results in this work have potential to promote the applications of SPGs and VA grippers in various material handling and robotics tasks.

Simple, Low-Cost Fabrication of Soft Sensors for Shape Reconstruction

Shape reconstruction by soft sensors may be useful in applications ranging from precision agriculture to haptics and factory automation due to the potential for low-cost fabrication, durable operation, and safe and compliant interaction. Current prevalent techniques, however, require expertise, expensive materials, and high-end processing equipment which limits both their transition to practice and their accessibility to researchers. To address this issue, we present easily accessible, low-cost, and rapid fabrication techniques for soft and resistive carbon composite sensors. We characterize their repeatability and durability in response to stretch up to 135%. We further show how this fabrication technique may be easily customized to two different applications, including a stretchable, tactile interface for passive sensing, and an active, soft pneumatic gripper that can fully encompass an object to reconstruct its shape. We complement these with simple control and analysis, and show how to achieve high relative accuracy, despite the high manufacturing tolerances of the sensors.

Soft Pneumatic Gripper With a Tendon-Driven Soft Origami Pump.

In this study, we propose a soft pneumatic gripper that uses a tendon-driven soft origami pump. The gripper consists of three pneumatic soft actuators that are controlled by a tendon-driven origami pump. An external air compressor that supplies air to the pneumatic actuator is replaced by an origami pump. The soft actuator is composed of silicone (Ecoflex 00-30) with a chamber-based structure, which is fabricated using a mold, and the origami pump is fabricated by folding a Kresling patterned polypropylene film. In addition, we conduct a series of experiments to evaluate the performance of the pneumatic actuator with a tendon-driven origami pump. Specifically, movement characteristics, frequency response, blocking force, and the relation between bending angle and pressure are analyzed from the results of the experiments. Furthermore, we understand the entire operation mechanism from the deformation of the origami pump to bending through pressure. Finally, we demonstrate the grasping of objects with diverse shapes and materials, and indicate the feasibility of the pneumatic gripper as an independent module without an external compressor.

Output Force Control of a Pneumatic Soft Gripper with a Jointed Endoskeleton Structure

Soft grippers are suitable for gripping various objects without damage owing to their high flexibility. But current soft grippers have a general problem of insufficient gripping force. To grip objects with different mass and sizes on assembly line safely and reliably, a novel pneumatic soft gripper with a jointed endoskeleton structure was developed and fabricated successfully. The actuation and force bearing functions of the gripper were separated to increase the gripping force. Moreover, to control the output force of the finger tip of the soft gripper, a fuzzy auto-tuning PID controller was designed and the relevant parameters of the controller were determined. Furthermore, a test platform with the designed fuzzy auto-tuning PID controller was developed to control the output force of the finger tip. The test results showed that the controller was able to maintain the desired target output force with a maximum deviation of 0.6 N. At last, the soft gripper was used to grip material objects for testing. From the experiment, it indicated that the output force of the finger tip can reach up to the desired values accurately and various objects can be gripped safely and reliably.

A Sensorized Hybrid Gripper to Evaluate a Grasping Quality Based on a Largest Minimum Wrench

Soft pneumatic grippers, which are based on soft pneumatic actuators have been widely studied owing to their simple morphological structure, inherent compliance, and pliable grasp. Additionally, the integration of the soft gripper with various sensors to improve its functionality has also been extensively studied. Although the soft gripper is known to exhibit a robust grasping performance without accurate control, the grasping quality of the soft gripper has rarely been studied due to the lack of adequate embedded sensors and quality metrics of the soft gripper. Therefore, a hybrid gripper, which is a soft gripper with rigid components, was sensorized by embedding a soft force sensor and a bending sensor to evaluate the grasping quality. Furthermore, a new grasping quality metric for a soft gripper was proposed, which calculates the largest minimum wrench of a convex hull in the wrench space. The proposed grasping quality metric was experimentally verified, and a real-time program was developed to evaluate the grasping quality.

Self-locking mechanism for variable stiffness rigid–soft gripper

Pneumatic soft grippers made of silicone have been successfully applied in the industrial field of grabbing fragile objects. But their inherent low stiffness often limits the practical application in scenarios required high stiffness or large load capacity. To expand the application of soft grippers, a self-locking mechanism realized by an exoskeleton structure is proposed in this work. The stiffness, load carrying capacity, and grabbing stability of this soft–rigid grippers can be enhanced in the premise of maintaining sufficient compliance. The resulted rigid–soft gripper has the ability of tuning its stiffness, simply by locking and unlocking the ratchet-and-pawl of the exoskeleton structure. The locking process is automatically implemented with the bending deformation of soft gripper, and the unlocking process is realized quickly by a simple pneumatic unlocking actuator. The stiffness, grasping motion and output force of the gripper are experimentally characterized theoretically and experimentally. And the capability of unlocking actuators is also verified and tested. Experimental results demonstrate that the rigid–soft gripper has a load capacity up to 9 kg. The gripper can achieve quick, flexible and reliable grasping for objects of various dimensions and shapes, with no compressed gas needed for holding. The proposed self-locking mechanism provides a simple but effective method to enhance the performance of soft grippers and simplify the operation for variable-stiffness grasping.