Compliant Gripper Research Articles

A New Two-Phase Design Process for a Compliant Mechanism Gripper

The structural design of the components with high accuracy and controllable motion is the focus of precision industries. As a result, researchers found that components created via compliant mechanisms were much preferable. Monolithic structures known as compliant mechanisms allow motion to be achieved without the need of traditional joints. The compliant mechanisms make it easier to build microscale devices because they do not have hard junctions. In this study, a novel two-phase design methodology for compliant mechanism forceps is proposed. In order to eliminate high-stress areas, forceps are often constructed as a distributed compliant mechanism. To offer a distributed planar design, topological optimization is introduced with new approach. Design domain introduced with pattern of holes restricts the single point contact formation and large area formation which yield distributed compliant mechanism. The parametrization technique is implemented to convert the conceptual design to working design. The design of compliant forceps is assessed using finite element analysis (FEA) based on structural considerations. Finally, a handle-equipped microgripper prototype has been developed. Experimental verification demonstrates the gripper's performance and variation is less than 3% with numerical results. Integerated force sensor measure the gripping force and compared the reaction force estimated through FEA.

Development of an Adaptive Force Control Strategy for Soft Robotic Gripping

Using soft materials in robotic mechanisms has become a common solution to overcome many challenges associated with the rigid bodies frequently used in robotics. Compliant mechanisms allow the robot to adapt to objects and perform a broader range of tasks, unlike rigid bodies that are generally designed for specific applications. However, soft robotics presents its own set of challenges in both design and implementation, particularly in sensing and control. These challenges are abundant when dealing with the force control problem of a compliant gripping mechanism. The ability to effectively regulate the applied force of a gripper is a critical task in many control operations, as it allows the precise manipulation of objects, which drives the need for enhanced force control strategies for soft or flexible grippers. Standard sensing techniques, such as motor current monitoring and strain-based sensors, add complexities and uncertainties when establishing mathematical models of soft grippers to the required gripping forces. In addition, the soft gripper creates a complex non-linear system, compounded by adding an adhesive-type sensor. This work develops a unique visual force sensor trained on synthetic data generated using finite element analysis (FEA) and implemented by integrating a non-linear model reference adaptive controller (MRAC) to control gripping force on a fixed 6-DOF robot. The robot can be placed on a mobile platform to perform various tasks. The virtual FEA sensor and controller, combined, are termed virtual reference adaptive control (VRAC). The VRAC was compared to other methods and achieved comparable control sensing and control performance while reducing the complexity of the sensor requirements and its integration. The VRAC strategy effectively controlled the gripping force by driving the dynamics to match the desired performance after a limited amount of training cycles. The controller proposed in this work was designed to be generally applicable to most objects that the gripper will interact with and easily adaptable to a wide variety of soft grippers.

Enhancing compliant gripper performance: Exploiting electro-adhesion to increase lifting force over grasping force

On the landscape of solutions to deal with delicate objects, the development and use of soft grippers is a topic of increasing interest, with a large number of prototypes proposed by the research community employing non-linear soft materials and based on diverse actuation means. However, increasing compliance usually leads to the reduction of lifting capacity. As a recent promising approach, shear forces exerted by a soft gripper can be enhanced by exploiting the electro-adhesion (EA) effect. Following this research trend, this paper proposes a new gripper that combines a compliant finger structure, with geometry taken from the FESTO FinRay but made of a softer material (a urethane rubber), and custom EA pads that are placed on the fingers at the interface with the grasped object. Following hyper-elastic model identification of the considered material and preliminary functional verification of gripper design via finite element simulations, the gripper is then manufactured and tested by means of a specific setup, replicating the grasping and lifting of cylindrical objects with different diameters. The results clearly show that the new gripper makes it possible to generate holding forces similar to those of the FESTO FinRay, but with significantly lower pressures on the grasped object (77 % less). Besides enabling the handling of more fragile items, the drastic increase in gripper compliance also results in lower mechanical actuation force (namely, 71 % less of gripping energy) required to generate the same holding force, with a consequent reduction of operation costs and sustainability of its application.

Soft Robotic System with Continuum Manipulator and Compliant Gripper: Design, Fabrication, and Implementation

This paper presents the design, construction, and implementation of a soft robotic system comprising a continuum manipulator arm equipped with a compliant gripper. Three main objectives were pursued: (1) developing a soft silicone gripper as an alternative to expensive and rigid steel grippers, enabling safe and precise handling of delicate or irregular objects such as fruits, glassware, and irregular shapes; (2) fabricating a continuum manipulator arm with robotic joints inspired by vertebrae, allowing for smooth, non-linear motion and more excellent maneuverability compared to traditional rigid arms, enabling access to hard-to-reach areas; and (3) integrating the compliant gripper with the continuum manipulator and implementing a control system for the soft gripper and remote bending arm using a microcontroller. The soft gripper, manipulator arm vertebrae, and other components were fabricated using 3D printing with PLA material for the molds. The gripper construct used hyperelastic silicone (Ecoflex 00.30). The continuum manipulator achieved a higher degree of freedom and mobility, while simulations and experiments validated the design’s effectiveness. The comparison shows that the close agreements differ by only 2.5%. In practical experiments involving lifting objects, the gripper was able to carry items with a greater mass. The proposed soft, integrated robotic system outperformed traditional rigid approaches, offering safe and flexible handling capabilities in unstructured environments. The nature-inspired design enabled a compliant grip and enhanced maneuverability, making it suitable for various applications requiring dexterous manipulation of delicate or irregularly shaped objects.

Development of a compliant gripper for safe robot-assisted trouser dressing-undressing

In recent years, many countries, including Japan, have rapidly aging populations, making the preservation of seniors' quality of life a significant concern. For elderly people with impaired physical abilities, support for toileting is one of the most important issues. This paper details the design, development, experimental assessment, and potential application of the gripper system, with a focus on the unique requirements and obstacles involved in aiding elderly or hemiplegic individuals in dressing and undressing trousers. The gripper we propose seeks to find the right balance between compliance and grasping forces, ensuring precise manipulation while maintaining a safe and compliant interaction with the users. The gripper's integration into a custom-built robotic manipulator system provides a comprehensive solution for assisting hemiplegic individuals in their dressing and undressing tasks. Experimental evaluations and comparisons with existing studies demonstrate the gripper's ability to successfully assist in both dressing and dressing of trousers in confined spaces with a high success rate. This research contributes to the advancement of assistive robotics, empowering elderly, and physically impaired individuals to maintain their independence and improve their quality of life.

An SMA-based compliant adjustable constant force gripper for micro-assembly

Ensuring precise and consistent force regulation in a confined workspace is critical for high-quality micro-assembly operations. To enhance structural efficiency and reduce system complexity, this study leverages the variable stiffness properties of the shape memory alloy (SMA) and presents a novel compliant adjustable constant force microgripper. In this work, a passive variable stiffness chained pseudo-rigid-body model is established to address the coupling analysis problem arising from the mechanical and SMA’s in-homogeneous phase transformation properties, thereby facilitating the integrated design of the SMA and the mechanism. Exploiting the variable stiffness property of SMA, an improved stiffness-tunable two-beam-binding constant force mechanism is proposed for the gripper jaws, which makes adjustable constant force operation via current control can be achieved straightforwardly. Further, inspired by differential actuation mode, a compact SMA-based actuator comprising two parallel guide mechanisms and SMA drivers is developed to meet the requirement for the large working stroke of the gripper. Numerical simulations and experimental studies validate the design model’s efficiency and the proposed structures’ capabilities, and also prove the gripper’s constant operation force value can be regulated in the range of 0.152 to 0.381 N. With dimensions of 35×56.5×7 mm3 and a maximum stroke of 2.077mm, the gripper demonstrates fine compactness and potential for continuous, cross-scale micro-assembly.

Design of a large stroke compliant gripping mechanism for constant-force applications

Design of a large stroke compliant gripping mechanism for constant-force applications

Modeling, simulations and experiments with generally routed cable-driven continuum robots and their application to three-fingered grippers

Abstract This paper deals with generally routed, pre-bent cable-driven continuum robots (CCR). A CCR consists of a flexible backbone to which multiple disks are attached. Cables are passed through holes in the disk, and when pulled, the flexible backbone and the CCR can attain different shapes based on their routing and backbone configuration. An optimization-based approach, using minimization of strain energy, is shown to give good results for the pose and motion of the CCR and to determine contact with external objects. The pose, motion, and the contact obtained from the model are shown to match very well with experimental results obtained from a 3D-printed CCR. An algorithm is proposed to generate the pre-bent backbone for a CCR which on actuation can attain the desired shape. Using the algorithm, three 3D-printed CCRs with pre-bent backbones are fabricated and these are used to demonstrate a compliant gripper that can grip a spherical object similar to that done by tentacles, and another three-fingered gripper with straight backbone CCRs is used to orient a square object gripped at the end.

Prototyping of compliant grippers using FFF and TPU

PurposeThe purpose of this paper is to investigate the process of fused filament fabrication (FFF) of a compliant gripper (CG) using thermoplastic polyurethane (TPU) material. The paper studies the applicability of different CG designs and the efficiency of some design parameters.Design/methodology/approachAfter reviewing a number of different papers, two designs were selected for a number of exploratory experiments. Using design of experiments (DOE) techniques to identify important design parameters. Finally, the efficiency of the parts was investigated.FindingsThe research finds that a simpler design sacrifices some effectiveness in exchange for a remarkable decrease in production cost. Decreasing infill percentage of previous designs and 3D printing them, out of TPU, experimenting with different parameters yields functional products. Moreover, the paper identified some key parameters for further optimization attempts of such prototypes.Research limitations/implicationsThe cost of conducting FFF experiments for TPU increases dramatically with product size, number of parameters studied and the number of experiments. Therefore, all three of these factors had to be kept at a minimum. Further confirmatory experiments encouraged.Originality/valueThis paper addresses an identified need to investigate applications of FFF and TPU in manufacturing functional efficient flexible mechanisms, grippers specifically. While most research focused on designing for increased performance, some research lacks discussion on design philosophy, as well as manufacturing issues. As the needs for flexible grippers vary from high-performance grippers to lower performance grippers created for specific functions/conditions, some effectiveness can be sacrificed to reduce cost, reduce complexity and improve applicability in different robotic assemblies and environments.

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.

Hitchhiker: A Quadrotor Aggressively Perching on a Moving Inclined Surface Using Compliant Suction Cup Gripper

Perching on the surface of moving objects, like vehicles, could extend the flight time and range of quadrotors. Suction cups are usually adopted for surface attachment due to their durability and large adhesive force. To seal on a surfaces, suction cups must be aligned with the surface and possess proper relative tangential velocity. However, quadrotors’ attitude and relative velocity errors would become significant when the object surface is moving and inclined. To address this problem, we proposed a real-time trajectory planning algorithm. The time-optimal aggressive trajectory is efficiently generated through multimodal search in a dynamic time-domain. The velocity errors relative to the moving surface are alleviated. To further adapt to the residual errors, we design a compliant gripper using self-sealing cups. Multiple cups in different directions are integrated into a wheel-like mechanism to increase the tolerance to attitude errors. The wheel mechanism also eliminates the requirement of matching the attitude and tangential velocity. Extensive tests are conducted to perch on static and moving surfaces at various inclinations. Results demonstrate that our proposed system enables a quadrotor to reliably perch on moving inclined surfaces (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.07m/s$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90^\circ$</tex-math> </inline-formula> ) with a success rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$70\%$</tex-math> </inline-formula> or higher. The efficacy of the trajectory planner is also validated. Our gripper has larger adaptability to attitude errors and tangential velocities than conventional suction cup grippers. The success rate increases by 45% in dynamic perches. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper was motivated by the problem of perching on moving inclined surfaces using quadrotors. It can be used for perching on the various angled surfaces of an automobile to save energy and enlarge flight distance. It can also be exploited in air-ground cooperative tasks. In recent years, various grippers and trajectory planning methods have been devised to enable quadrotors to perch on static inclined surfaces. These strategies can not be used for perching on moving inclined surfaces. The task poses high requirements for the efficiency of trajectory planning and the grippers’ adaptability to pose errors. This paper proposes a real-time planning method to generate trajectories. The trajectories respect kinematic and motor lift constraints. They allow large attitude maneuvering of quadrotors. A multimodal search in a dynamic time-domain is developed to seek the minimum feasible time for the trajectory planner. Considering large pose errors in dynamic perching, a compliant gripper based on multiple independent suction cups is designed. The wheel and multidirectional layout of cups increase the adaptability to attitude and velocity errors. Results suggest that the proposed system is effective and reliable. In practice, our multiple cups would add weight penalty and increase the drag. The suction cups should be placed close to a quadrotor’s central axis to reduce the drag and disturbance in flow. The proposed system relies on an external motion capture system. In future research, we will focus on onboard sensing and control methods to achieve perching on moving inclined surfaces outdoors.

Simulation of SMA-based engineering applications considering large displacement and rotation, thermomechanical coupling and partial phase transformation

Shape memory alloys (SMAs) undergo large recoverable deformation due to their inherent diffusionless martensitic phase transformation. Two factors need to be taken into account to incisively emulate the behaviour of SMA based structures: (i) consideration of large displacement and rotation (LDR) effect, and (ii) capturing the consequence of transformation induced material level coupling. In this study, both these effects are apprehended by extending the infinitesimal strain-based constitutive model of SMA as proposed by Lagoudas et al. (2012), assuming small elastic strain but with finite inelastic strain. To preclude any spurious stress generation out of large rotation, the Jaumann stress rate is used, and incremental objectivity for finite rotation between two successive time instants is conserved by rotating the strain increment and spin tensor to the rotation-independent mid-point configuration following Hughes–Winget (Hughes and Winget, 1980) algorithm. In addition, the contribution of thermoelastic and latent heat evolved during transformation is taken into consideration in the thermal equilibrium equation. Moreover, the effect of partial phase transformation yielding minor hysteresis loop has also been captured. The equilibrium equation is expressed in the current configuration following the Updated Lagrangian formulation. The mechanical and thermal equilibrium equations are solved concurrently in block matrix form using the Newton–Raphson (NR) iterative technique, considering the coupling terms resulting from the phase transformation. The efficacy and robustness of the developed finite element model are corroborated through various practical applications of SMA-based members, e.g., SMA ring, SMA-actuated beam, morphing of corrugated airfoil, orthodontic palatal expander, compliant gripper, undergoing LDR while subjected to different thermomechanical loading conditions. The combined effects of LDR along with thermomechanical coupling yield a stiffening behaviour during loading and sluggish response at the time of thermal recovery.

Design and Implementation of a Compliant Gripper for Form Closure of Diverse Objects

This research presents a comprehensive study on the design and implementation of a flexible robotic gripper. Conventional grippers utilized in articulated robotic arms are often limited in their capabilities, being restricted to specific tasks or fixed object sizes. While soft grippers are a viable option, they have limitations in terms of grasping objects across a wide range and providing complete coverage. In this study, a novel compressible gripper is developed to enable safe and secure grasping of objects with varying sizes and shapes within a wide range. The gripper features a grasping area measuring 14 cm × 6 cm, allowing complete coverage of objects within this surface area. The current prototype with 7 cm of compressibility demonstrates the ability to grasp objects with a width difference of 7 cm with a maximum thickness of 15 cm, enabling manipulation of objects with varying widths, as defined by user-programmable parameters. The functionality of the gripper is based on the compressibility of the 3D-printed thermoplastic polyurethane (TPU) material. The flexible part of the gripper can be easily interchanged, offering versatility by accommodating different thicknesses without the need to replace the entire gripper mechanism. The gripper system operates using an open-loop control system, enhancing user-friendliness. Experimental evaluation of the gripper involved the creation and analysis of a CAD model followed by the fabrication of a prototype. The prototype exhibited exceptional performance in grasping objects of diverse sizes, shapes, and textures, demonstrating the effectiveness of the developed soft gripper system. The scalability of the soft gripper enables seamless integration with various types of articulated robotic arms, while the maximum weight limit for objects will be defined based on the robotic arms’ limitations. The research findings highlight the promising capabilities of the compressible gripper in enhancing the versatility and efficiency of robotic grasping systems, offering a significant contribution to the field of robotics.

PENERAPAN MEKANISME COMPLIANT PADA MEKANISME GERAK GRIPPER

Innovation is a term for applying an idea that can form a new product or improve an existing product. The parallelogram shape is the most popular mechanism used in gripper because of its configuration that causes the tip to hold its orientation when closed and open. The drawback of this form is the large number of components needed and requires an assembly process in order to achieve the desired motion. A compliant mechanism can overcome this shortcoming because objects can be made simpler without the need for an assembly process. The advantages and disadvantages of the compliant gripper have been obtained from the design, test results, and comparisons. The design obtained with dimensions of P 186.27 X W 157.55 X H 10 mm uses a leaf-type flexure with varying thickness. The thicker it is the greater the force required to use the gripper. the results printed using a 3d printer also reflect the data that has been obtained regarding the style. The thinner the flexure, the more susceptible the tool is to external forces such as shocks. The comparisons made show that the advantages of the gripper are the minimum required components, no assembly process required, and a smaller mass compared to the reference mechanism. Disadvantages obtained are the decrease in the width of the opening distance and the orientation of the finger that changes according to changes in the angle at the fulcrum.

Clamping force manipulation in 2D compliant gripper topology optimization under frictionless contact

Clamping force manipulation in 2D compliant gripper topology optimization under frictionless contact

Insect Tarsus-Inspired Compliant Robotic Gripper With Soft Adhesive Pads for Versatile and Stable Object Grasping

Grasping multiple object types (versatile object grasping) with a single gripper is always a challenging task in robotic manipulation. Different types of grippers, including rigid and soft, have been developed to try to achieve the task. However, each gripper type is still restricted to specific object types. In nature, many insects can be observed to use only one tarsus mechanism to cope with several tasks. They have a very high grasping capability with objects and can adhere to a variety of surface types. Inspired by insect tarsus, this paper proposes a novel underactuated, single cable-driven, compliant gripper design. The structure of the gripper is based on the hornet tarsus morphology with a proportional scale. An additional pulley-like structure is introduced to increase the generated grasping torque. To maintain the ability to automatically rebound back to the original position, a torsion spring is implemented at each joint. In order to stably grasp and hold objects, soft adhesive pads with an asymmetric sawtooth-like surface structure are attached at the tarsus segments. The performance of this insect tarsus-inspired gripper with the soft pads is evaluated by grasping 35 different objects of various sizes, shapes, and weights for comparison with industrial soft and rigid grippers. The proposed gripper shows a 100% success rate in grasping all objects, while the soft and rigid gripper success rates are 81.90% and 91.43% on average, respectively. We finally demonstrate the use of our gripper installed on a robot arm for pick-and-place and pouring tasks.

Design of an SMA-driven compliant constant-force gripper based on a modified chained pseudo-rigid-body model

Compliant grippers are important devices for assembling small parts. Analyzing the mechanism efficiently and accurately and designing grippers carefully have also become crucial. In this paper, a shape memory alloy-driven compliant constant-force gripper is developed to create extensive and safe operations. A modified chained pseudo-rigid-body model with additional prismatic pairs is proposed for optimal performance according to mechanical analysis. In the developed gripper, a two-beam binding constant-force mechanism is proposed to apply a constant gripping force in the gripper’s jaws; a constant-force guide mechanism is utilized to extend the actuation stroke and connect the jaws with the actuator. The simulation results of the functional parts are in good agreement with the theoretical results, demonstrating the high accuracy of the proposed beam model. In addition, experimental studies on the gripping force and grasp-release operations verify the effectiveness of the designed gripper and its components.

Compliant Suction Gripper With Seamless Deployment and Retraction for Robust Picking Against Depth and Tilt Errors

Applying suction grippers in unstructured environments is a challenging task because of depth and tilt errors in vision systems, requiring additional costs in elaborate sensing and control. To reduce additional costs, suction grippers with compliant bodies or mechanisms have been proposed; however, their bulkiness and limited allowable error hinder their use in complex environments with large errors. Here, we propose a compact suction gripper that can pick objects over a wide range of distances and tilt angles without elaborate sensing and control. The spring-inserted gripper body deploys and conforms to distant and tilted objects until the suction cup completely seals with the object and retracts immediately after, while holding the object. This seamless deployment and retraction is enabled by connecting the gripper body and suction cup to the same vacuum source, which couples the vacuum picking and retraction of the gripper body. Experimental results validated that the proposed gripper can pick objects within 79 mm, which is 1.4 times the initial length, and can pick objects with tilt angles up to 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> . The feasibility of the gripper was verified by demonstrations, including picking objects of different heights from the same picking height and the bin picking of transparent objects.

Design and Control of Monolithic Compliant Gripper Using Shape Memory Alloy Wires.

This paper presents the design, fabrication and testing of a shape memory alloy (SMA)-actuated monolithic compliant gripping mechanism that enables translational motion of the gripper tips for grasping operation suitable for micromanipulation and microassembly. The design is validated using a finite element analysis (FEA), and a prototype is created for experimental testing. The reported gripping structure is simple and easy to build and design. The gripper is demonstrated to have a displacement amplification gain of 3.7 that allows maximum tip displacement up to 1.2 cm to possess good handling range and geometric advantage which cannot be accomplished by conventional grippers. The position of the gripper tip is predicted from the variation in the electrical resistance of the SMA wire based on the self-sensing phenomena. Self-sensing actuation of the SMA allows the design of a compact and lightweight structure; moreover, it supports the control loop/scheme to use the same SMA element both as an actuator and sensor for position control. The geometrical dimensions of the SMA wire-actuated monolithic compliant gripper is 0.09 m × 0.04 m and can be operated to handle objects with a maximum size of 0.012 m weighing up to 35 g.

A Compliant Teleoperation System by Utilizing Haptic Guidance and Series Elastic Actuator-Based Gripper

Abstract This article introduces a haptic-guided teleoperation framework using a series elastic actuator (SEA)-based compliant gripper. The proposed teleoperation system involves one local haptic device, one layer of virtual reality, and one remote industrial manipulator with a compliant gripper. The overall compliance of the teleoperation is distributed between the software and hardware components of the bilateral loop. On the one hand, the implemented haptic guidance is based on an elementary coupling model uniquely defined and established for all interactions among the user, remote manipulator, and virtual interface. On the other hand, the manipulator operating in the remote environment is equipped with a novel compliant gripper based on series elastic actuators, providing passive compliance at the interactions with the environment. Introducing the gripper into the haptic loop is expected to compensate for disturbances due to inaccurate modeling and/or unmodeled dynamics of the remote environment and external effects. The teleoperation system is implemented for manipulation and tracking tasks and tested with different users. Experimental results show that the haptic guidance and the compliant gripper together significantly improve the teleoperation performances in terms of transparency.