Pneumatic Grippers Research Articles

Design and development of a variable structure gripper with electroadhesion

Soft grippers are a novel kind of front-end actuators for robotics that offer great benefits such as easy control, superior grabbing capability, and close contact with the environment. They have vast application possibilities in numerous industries such as agricultural picking, item sorting, and medical rehabilitation. In this paper, a soft gripper with a variable structure and electrostatic adsorption is proposed. The gripper includes three fingers uniformly dispersed in the shape of a circle, which can adapt to varying sizes of grabbing objects by dynamically modifying the opening angle of the fingers. Aimed at addressing the existing issue of lacking multi fingers soft pneumatic grippers (SPGs) in grabbing tiny flat items, it is enhanced by embedding an electroadhesion (EA) films at the bottom of the soft pneumatic fingers of the gripper. It is simulated that the diameter adjustment range of this gripper is 0–482 mm, and the angle adjustment range is 0–180° via ABAQUS simulation. Finally, the adaptive grabbing capacity of the soft gripper was validated via experiments. The trials reveal that the gripper can grab items of different sizes by altering the opening angle of the fingers and the maximum load of the gripper can reach 10.91 N during specific grasping operations. The findings confirm that the SPGs with variable structure and EA described in this paper has a high gripping range and the capacity to grab thin flat items. We believe that its excellent gripping performance will encourage different uses of this gripper in everyday life and industry.

The Enhanced Adaptive Grasping of a Soft Robotic Gripper Using Rigid Supports

Soft pneumatic grippers can grasp soft or irregularly shaped objects, indicating potential applications in industry, agriculture, and healthcare. However, soft grippers rarely carry heavy and dense objects due to the intrinsic low modulus of soft materials in nature. This paper designed a soft robotic gripper with rigid supports to enhance lifting force by 150 ± 20% in comparison with that of the same gripper without supports, which successfully lifted a metallic wrench (672 g). The soft gripper also achieves excellent adaptivity for irregularly shaped objects. The design, fabrication, and performance of soft grippers with rigid supports are discussed in this paper.

Development of a suction gripper network based on the biological role model of an octopus

The handling of fragile, sensitive or flexible components in assembly technology and production requires grippers that are designed for gentle handling of the objects to be gripped. Suction grippers are still a widespread standard solution for this purpose. However, rising energy prices are making pneumatic grippers, which work with a central upstream compressed air supply, increasingly unattractive. The generation of the compressed air itself, the mostly leaky transmission and the relatively inefficient vacuum generation are cost drivers that many users would like to avoid. Consequently, vacuum-based gripper means are required for industrial production, which work without externally generated compressed air. At the Fraunhofer IWU, a compressed-air-free suction pad composite has been developed that enables gripping of components with a wide variety of shapes. The underlying concept is inspired by the function of the suction arms (tentacles) of an octopus. By evacuating several small volume areas, which can be individually mechanically actuated, safe and sensitive gripping of objects is possible. For the generation of the vacuum, a piston system and a principle of an artificial muscle were developed, which is controlled based on shape memory alloys.

Research Progress on Low Damage Grasping of Fruit, Vegetable and Meat Raw Materials.

The sorting and processing of food raw materials is an important step in the food production process, and the quality of the sorting operation can directly or indirectly affect the quality of the product. In order to improve production efficiency and reduce damage to food raw materials, some food production enterprises currently use robots for sorting operations of food raw materials. In the process of robot grasping, some food raw materials such as fruits, vegetables and meat have a soft appearance, complex and changeable shape, and are easily damaged by the robot gripper. Therefore, higher requirements have been put forward for robot grippers, and the research and development of robot grippers that can reduce damage to food raw materials and ensure stable grasping has been a major focus. In addition, in order to grasp food raw materials with various shapes and sizes with low damage, a variety of sensors and control strategies are required. Based on this, this paper summarizes the low damage grasp principle and characteristics of electric grippers, pneumatic grippers, vacuum grippers and magnetic grippers used in automated sorting production lines of fruit, vegetable and meat products, as well as gripper design methods to reduce grasp damage. Then, a grasping control strategy based on visual sensors and tactile sensors was introduced. Finally, the challenges and potential future trends faced by food robot grippers were summarized.

Grasping Profile Control of a Soft Pneumatic Robotic Gripper for Delicate Gripping

Soft pneumatic grippers (SPGs) have garnered significant attention and recognition in various industries owing to their remarkable flexibility, safety, and adaptability. They excel in manipulating delicate, irregularly shaped, and soft objects, surpassing the limitations of conventional grippers. However, effective control techniques for managing the grasping profile of SPGs are still under development. Simple on–off pressure control using a regulator valve is inadequate for delicate gripping with pneumatic robot grippers. To address this, a synergy pressure control system was implemented. In addition, a proportional–integral–derivative control technique, complemented by an unknown input observer, was devised to control the volume of the soft pneumatic robotic gripper, ensuring its alignment with the desired volume level. The simulation and experimental results provide substantial evidence of the effectiveness of the developed control technique and the unknown input observer in managing the volume and pressure of the gripper. Consequently, this breakthrough empowers precise and delicate gripping actions, enabling the handling of delicate objects such as tofu.

Advanced Stiffness Sensing through the Pincer Grasping of Soft Pneumatic Grippers.

In this study, a comprehensive approach for sensing object stiffness through the pincer grasping of soft pneumatic grippers (SPGs) is presented. This study was inspired by the haptic sensing of human hands that allows us to perceive object properties through grasping. Many researchers have tried to imitate this capability in robotic grippers. The association between gripper performance and object reaction must be determined for this purpose. However, soft pneumatic actuators (SPA), the main components of SPGs, are extremely compliant. SPA compliance makes the determination of the association challenging. Methodologically, the connection between the behaviors of grasped objects and those of SPAs was clarified. A new concept of SPA modeling was then introduced. A method for stiffness sensing through SPG pincer grasping was developed based on this connection, and demonstrated on four samples. This method was validated through compression testing on the same samples. The results indicate that the proposed method yielded similar stiffness trends with slight deviations in compression testing. A main limitation in this study was the occlusion effect, which leads to dramatic deviations when grasped objects greatly deform. This is the first study to enable stiffness sensing and SPG grasping to be carried out in the same attempt. This study makes a major contribution to research on soft robotics by progressing the role of sensing for SPG grasping and object classification by offering an efficient method for acquiring another effective class of classification input. Ultimately, the proposed framework shows promise for future applications in inspecting and classifying visually indistinguishable objects.

Design of squeezing-tube-driven pump for soft pneumatic robotics based on spiral spring winding

Aiming at the demand for high-speed, easy-controllability, and integration of pneumatic soft robots and elastomer actuators, this study presents a squeezing-tube-driven pump (STDP) for soft pneumatic robotics based on spiral spring winding. This concept contains a customized spiral spring and a pneumatic tube with high-elasticity. The spiral spring is driven by an electric motor and coerced into winding deformation. Furthermore, the pneumatic tube is extruded by the spring and then the air in the tube is fast compressed to drive soft pneumatic grippers. The mechanical model and simulation are utilized to explain the operating principle of STDP. The air pressure and rotation angle of the spring under various rotation speeds are in a close linear correlation verified by the experimental results, which provides feasibility for easy controlling and rapid actuation. Finally, fast-gripping tests with an integrated gripper–pump system and a pneumatic muscle actuation test are presented to show the advantages of the proposed pump, respectively.

A Quadratic-Programming Approach for the Real-Time Control of the Fingers Position in Industrial Pneumatic Grippers

Industrial grippers are generally either electric or pneumatic, with the latter being preferred as their air-based functioning guarantees many advantages such as cost effectiveness and reduced encumbrance. Despite the very large employment, pneumatic grippers do not yet offer performance beyond the open/closed behavior in the majority of cases. Pneumatic grippers mounted on industrial robotic arms are commonly rigid as high forces might be required during the grasping operations. The poorness of the control strategies for the grasping force, as well as for the fingers position, does not match the great advancement that robotics obtained in the last years. Therefore, this letter intends to deliver a new control algorithm for the control of pneumatic grippers. The proposed algorithm permits to finely control the position of the gripper fingers, exploiting a quadratic-programming function to minimize the controller output. Different experiments are shown to demonstrate the algorithm effectiveness.

Adaptive Pincer Grasping of Soft Pneumatic Grippers Based on Object Stiffness for Modellable and Controllable Grasping Quality

In this study, adaptive pincer grasping of soft pneumatic grippers (SPGs) is considered, and we propose how the performance of soft pneumatic actuators (SPAs) and the stiffness of grasped objects can be accounted for in modeling and control. The grasping kinetics was analyzed. The connection between grasping quality and SPA performance is discussed. We also devised a subjective definition of grasping quality due to SPA performance. A modeling technique was established, which makes dominant factors of grasping quality due to the SPA performance predictable over the gripper input. Later, a control architecture was developed. This architecture demonstrates how the grasping is implemented. The modeling technique was used to forecast grasping quality due to the SPA performance and its factors. An experiment was conducted to obtain actual results. The predicted and actual results were correspondingly compared. The results show minute deviation, thereby validating the reliability of the grasping. This study clarifies the association between grasping quality and SPA performance and contributes an advancement toward modellable and controllable task-level variables, such as grasping quality, in SPG pincer grasping.

Optimal design and experimental validation of 3D printed soft pneumatic actuators

This study develops a novel design of a unit cell-based bending-type soft pneumatic actuator, and formulates the design problem as compliant mechanisms under design-dependent pressure loadings. The proposed design is first optimized by using a topology optimization algorithm, in which the design-dependent loads and fluid-structure interface are tracked and formulated via finite element based approaches. Then, to validate the optimized design, it is modeled numerically using finite element analysis (FEA) and compared with the non-optimized traditional rectangular design. The optimal design can provide 19.5% improvements in bending angle. In addition, the proposed optimal design is prototyped using 3D printing. The prepared single actuator specimens are tested under pneumatic pressure, and the measured deformations are compared with those obtained from FEA. The results reveal that the optimized design can undergo large and compliant deformations under pneumatic pressure and generate a full () bending. Furthermore, multiple actuator specimens of the proposed design are also assembled and integrated to prototype soft pneumatic grippers, with which several grasping tests are conducted. The adaptability and compatibility of the soft gripper are verified via gripping a wide range of irregular, soft, and fragile objects.

A Bionic pipe-crawling soft robot based on the pneumatic silicone actuator

To realize the real-time monitoring of pipelines, this paper designs a pneumatic soft pipeline outer wall-crawling robot composed of OMCA (outer multi-cavity actuator) based on the motion of the inchworm. The robot consists of a torso and two pneumatic grippers. It is controlled by three air pumps and can realize pipeline linear motion. Use ABAQUS to perform finite element analysis on OMCA and measure its key geometric parameters under different pressure levels, and then test the robot’s kinematic performance. The movement speed of the robot on a pipe with a diameter of 10 cm is 0.3 mm/s.

A Soft Pneumatic Gripper with Endoskeletons Resisting Out-of-Plane Bending

The established soft pneumatic grippers have the benefit of flexible and compliant gripping, but they cannot withstand lateral loads, due to the low stiffness of soft material. This paper proposes an endoskeleton gripper. The soft action of the finger is performed by air chambers, and the gripping force is transferred by the rigid endoskeleton within the finger. The endoskeleton in the finger is similar to a wristwatch chain; the hinge mechanism permits relative rotation in the working plane but restricts out-of-plane bending, greatly increasing the finger stiffness. The endoskeleton and gripper holder can be 3D-printed with CR-PLA material. The finger was fabricated by molding of silicone gel. The gripper can perform enveloping grasping and pinch grasping operations depending on the object size, weight, and surrounding environment. The finger bending and gripper grasping performance were investigated by experiments and finite element analysis. The fingertip force of the endoskeleton gripper was about 1.45 times higher than that of the gripper without endoskeleton. It was found that the gripper can grasp objects with a maximum diameter of 80.5 mm and a weight of 450 g, which were 80.5% of the finger length and six times the finger self-weight, respectively.

Influence of Inlet Parameters on Power Characteristics of Bernoulli Gripping Devices for Industrial Robots

There is a wide variety of gripping devices with various parameters at the present stage of development of robotics. However, the existing literature about the power characteristics of pneumatic gripping devices does not provide any analysis of the different types of input parameters other than supply pressure and flow characteristics, whereas the input parameters completely determine the technical characteristics of the gripping devices of industrial robots. In particular, for pneumatic grippers, the input parameters play a crucial role in their productivity and energy efficiency. This paper fills the gap by providing a study of the impact of such parameters on the power and energy characteristics of Bernoulli ejection grippers for industrial robots, including: the parameters of the compressed air inlet design, the parameters of the fitting for compressed air supply, the diameter of the hose for compressed air supply, and the size of the vacuum zone. First, this paper presents the results of theoretical studies and finite element method for determining the distribution of pressure on the surface of an object of manipulation, which allows one to determine the lifting force of the Bernoulli gripping devices of an industrial robot. It is determined that the horizontal air flow to the capture chamber, compared with that of the vertical, should be used to ensure the maximum possible lifting force. Structures and constriction in fittings, which are used to supply compressed air to the chamber of Bernoulli gripping devices, are considered. Then, the dependencies of the influence of narrowing the fittings on the power characteristics of gripping devices are presented.

Soft robotic surface enhances the grasping adaptability and reliability of pneumatic grippers

Soft grippers are an emerging field of robotics in recent years owing to their reduced control complexity, easy fabrication, and excellent compliance. However, the small contact area and force usually limit their grasping reliability. Herein, a soft gripper consisting of two soft robotic surfaces (SRSs) is proposed inspired by Venus flytrap, which can provide enveloping and pinching grasp modes. To guide the design of the gripper, an analytical model of the SRS is developed for both bending inward and outward. The experimental results show an excellent agreement with analytical results, which demonstrates the validity of the analytical model. Additionally, the grasping performance of the soft gripper is investigated experimentally. The results indicate that the grasp and pull-off force depend on the size and shape of objects and applied pressure. As the applied pressure is 60 kPa, the maximum grasp force and pull-off force reach 0.71 N and 8.15 N, respectively. Various grasping experiments are also conducted to study the effect of diverse objects, errors of object position, and SRS installation on the grasping capacity. Our findings demonstrate that our gripper can observably enhance the grasping adaptability and reliability due to the high passive compliance of the SRS allowing a large contact area between the gripper and objects.

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.

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

We performed dynamic pressure buckling experiments on defect-seeded spherical shells made of a common silicone elastomer. Unlike in quasi-static experiments, shells buckled at ostensibly subcritical pressures, i.e. below the experimentally determined critical load at which buckling occurs elastically, often following a significant delay period from the time of load application. While emphasizing the close connections to elastic shell buckling, we rely on viscoelasticity to explain our observations. In particular, we demonstrate that the lower critical load may be determined from the material properties, which is rationalized by a simple analogy to elastic spherical shell buckling. We then introduce a model centred on empirical quantities to show that viscoelastic creep deformation lowers the critical load in the same predictable, quantifiable way that a growing defect would in an elastic shell. This allows us to capture how both the deflection at instability and the time delay depend on the applied pressure, material properties and defect geometry. These quantities are straightforward to measure in experiments. Thus, our work not only provides intuition for viscoelastic behaviour from an elastic shell buckling perspective but also offers an accessible pathway to introduce tunable, time-controlled actuation to existing mechanical actuators, e.g. pneumatic grippers.

Radiation-tolerant robotic complex URS-2

The results of the development of a radiation-tolerant robotic complex URS-2 for operation in hot cells at nuclear enterprises are presented. The robotic complex consists of several original components: robotic arm, control device with force feedback, control panel with hardware buttons and touch screen, control computer with system and application software, control-and-power cabinet. The robotic manipulator has 6 degrees of freedom, replaceable pneumatic grippers and is characterized by high radiation tolerance, similar to that of mechanical master-slave manipulators. The original design of the control device based on the delta-robot model that implements a copying mode of manual control of the robotic complex with force feedback is presented. The hardware and software solutions developed has made it possible to create a virtual simulator of the RTC for testing innovative methods of remote control of the robot, as well as teaching operators to perform technological tasks in hot cells. The experimental model of the robotic complex has demonstrated the ability to perform basic technological tasks in a demo hot cell, both in manual and automatic modes.

Self-tuning hybrid fuzzy sliding surface control for pneumatic servo system positioning

This paper presents a new robust control strategy developed for the pneumatic servo system (PSS) by hybridizing two types of fuzzy logic control (FLC) rules as a self-tuner to the integral sliding mode control (ISMC), namely self-tuning hybrid fuzzy sliding surface control (SH-FSSC) controller. A sliding surface consisting of two switched fuzzification rules, relying on the tuning threshold value of the position error tracking, was designed to consider both the position and the force feedback of the pneumatic proportional valve with a double-acting cylinder (PPVDC) system. The approach is to acquire multiple features not only on tracking error but also faster transient response with finite-time convergence, chatter elimination, and robustness against uncertainty. The proposed control strategy was verified and validated by conducting experiments with the actual PPVDC unit linked to the tip of the robot’s tri-finger pneumatic grippers (TPG) platform. The experimental works were accomplished using two types of input trajectories: multi-steps and sinusoidal input trajectories. On the other hand, an additional external payload as a disturbance to the test rig has also been added at the end of the pneumatic gripper jaw, intended to evaluate the proposed controller’s robustness performance. The advantage of the proposed method was validated by significantly eliminating oscillation for each transient response, maintaining high tracking performance, and minimizing hysteresis effects. The oscillation was suppressed with minimal overshoot, and the proposed method was achieved without a significant loss of performance.

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.