Design of a bidirectional compliant gripper for robotic object manipulation

Bistable compliant underactuated gripper for the gentle grasp of soft objects

Although a compliant gripper is a type of compliant mechanism, existing analytical models rarely account for the real mechanical behavior of the flexible parts within the gripper. In this work, an in-plane motion flexure-based compliant gripper is presented, modeled, and analyzed. An analytical methodology based on the Compliance Matrix Method (CMM) is proposed to compute the relationship between input and output forces and displacements in two different coordinate frames using a single unified expression that represents the real mechanical behavior of the system. The analytical model is validated through Finite Element Analysis (FEA) simulations and experimental tests performed on additively manufactured prototypes. Additionally, the model is used to analyze output displacements resulting from variations in geometric parameters, with results validated through FEA simulations. This demonstrates the method’s utility in optimizing gripper design during early development stages prior to fabrication. The proposed analytical model accurately estimates the compliant gripper’s kinetostatic behavior, achieving less than 5% difference compared to FEA and experimental results. Furthermore, the model is adaptable and can be extended for the kinetostatic analysis of other compliant grippers with similar flexure-based architectures.

This paper presents the design of a multimode compliant gripper, using the singularities of the four-bar mechanism with equilateral links. The mobility of the compliant gripper can be reconfigurable to grasp a variety of shapes or adapt to specific requirements. The compliant gripper is a compact and two-layer structure. Two linear actuators are required to enable the multiple operation modes, by the conversion of two pairs of slider-crank mechanisms. A multimode compliant four-bar mechanism is first presented and kinematically analyzed. The design and the kinetostatic modeling of the resulting compliant gripper are then performed. Finally, the analysis of the reconfigurable compliant gripper under different actuation schemes is carried out, including the comparison of the results obtained from analytical modeling, finite element analysis (FEA), and experimental testing.

The prerequisite for new versatile grippers is the capability to locate and perceive protests in their surroundings. It is realized that automated controllers are profoundly nonlinear frameworks, and a faultless numerical model is hard to get, in this way making it troublesome to control utilizing tried and true procedure. Here, a design of an adaptive compliant gripper is presented. This design of the gripper has embedded sensors as part of its structure. The use of embedded sensors in a robot gripper gives the control system the ability to control input displacement of the gripper and to recognize specific shapes of the grasping objects. Since the conventional control strategy is a very challenging task, soft computing based controllers are considered as potential candidates for such an application. In this study, the polynomial and radial basis function (RBF) are applied as the kernel function of Support Vector Regression (SVR) to estimate and predict optimal inputs displacement of the gripper according to experimental tests and shapes of grasping objects. Instead of minimizing the observed training error, SVR poly and SVR rbf attempt to minimize the generalization error bound so as to achieve generalized performance. The experimental results show that an improvement in predictive accuracy and capability of generalization can be achieved by the SVR approach compared to other soft computing methodology.

The adaptive compliant gripper with passive fingers can achieve both a more compact structure and better application versatility. However, the conceptual design of passive fingers is difficult and lacks relevant design method. To solve this problem, this paper proposes an active-deformation-aided strategy for the topology optimization of passive finger structure. This strategy utilizes an auxiliary input force to enlarge the output deformation and enable feasible synthesis of passive fingers. The influence of virtual spring stiffness on the optimization results is studied. Based on two designed passive fingers, two compliant grippers are developed to further evaluate their grasping performances. The designed grippers are verified by finite element analysis and experiments, and compared with the fin-ray effect gripper. The results show that the designed passive grippers exhibit excellent adaptability and grasping performance. This paper provides two novel structures of passive finger. The proposed design strategy can facilitates the design of the adaptive grippers with passive finger structure.

Design of a compliant adjustable constant-force gripper based on circular beams

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

Design and static testing of a compact distributed-compliance gripper based on flexure motion

Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shapes and surfaces is a very challenging task. This paper presents an approach of the new principle of a universal gripper with adaptable shape morphing surfaces. The adaptive surfaces will have the controllability by a compliant system with embedded actuators and sensors. The main sensing system has to be made of a conductive silicone rubber or foam. These are carbon-black filled silicone materials with good sensing properties whose electrical resistance is changed by compression. The implemented controllable system will be able to morph shapes of the gripper to accommodate different objects. A methodology for design of the compliant adaptive gripper will be presented. The main advantage of this compliant gripper is the connection of controllability and observability in one system by a compliant mechanism.

This paper presents the design, modeling, fabrication, and test of a monolithic compliant gripper for micro-manipulation applications. A compact compliant mechanism that enables in-principle straight-line parallel jaw motion is obtained, by combining the Scott–Russell mechanism and the parallelogram mechanism. The right-circular corner-filleted (RCCF) flexure hinge is adopted to achieve a large displacement of lumped-compliance joints. A pseudo-rigid-body model (PRBM) method with the help of the virtual work principle is performed to obtain parametric analytical models including the amplification coefficient and kinetostatics. Finite element analysis (FEA) is conducted to validate the analytical model and capture adverse parasitic motions of jaws. A monolithic prototype was fabricated, the test results of which show satisfactory performances.

This paper presents a topology optimization method of compliant grippers considering stress constraints. The proportional topology optimization (PTO) algorithm is applied to the design of compliant grippers, and it is improved by introducing weight factors into the objective function and adding stress conditions on the basis of constraints. In the current gradient modeling of topology optimization, the global maximum stress is measured by P-norm function, and its sensitivity analysis of stress constraints is derived by adjoint equations. It is worth noting that more rigorous gradient calculations are employed in stress problems and their computation brings an additional computational burden. By contrast, the non-gradient method using PTO algorithm allocates design variables to the element proportionally according to the values of stress. It can eliminate difficulties in the analytical derivation and calculation of gradient, and improve the calculation efficiency. Subsequently, performances of compliant grippers generated by these two methods are compared through finite element analysis. Finally, the optimized compliant gripper prototype is manufactured by three-dimensional (3D) printing using flexible thermoplastic urethane. Experimental results indicate that the non-gradient method is effective, and the optimized compliant gripper has excellent characteristics of low stress and high output performance.

A compliant gripper gains its dextral manipulation by the flexural motion of its fingers. It is a preferable device to grippers with actuations because of reduced fabrication complexity and increased structural reliability. The prediction of contact forces and deflected shape are essential to the design of a compliant gripper. We present here a formulation based on nonlinear constrained optimization (NCO) techniques to analyze contact problems of compliant grippers. For a planar compliant gripper this formulation essentially reduces the domain of discretization by one dimension. Hence it requires simpler formulation and is computationally more efficient than other methods such as finite element analysis. As this method is rather generic, its use would facilitate design analysis and optimization of compliant devices. We illustrate these attractive features with two types of compliant grippers; macro-handling and micro-assembly applications

This paper presents the design and testing of a novel flexure-based compliant parallel gripper with constant driving force. One uniqueness of the gripper lies in that it achieves two-degree-of-freedom (2-DOF) independent constant driving force in grasping and rolling operations. In each direction, the grasping and rolling operation is executed with the constant driving force. The parallel-kinematic flexure mechanism design enables nearly decoupled operations in 2-DOF manipulation. The constant driving force property enlarges the grasping range by reducing the required driving force. Analytical modeling of the gripper mechanism is carried out based on pseudo-rigid-body method, which is verified by conducting simulation study with nonlinear finite-element analysis (FEA). Parametric study is conducted to investigate the influence of each design variable on the gripper performance. To demonstrate the performance of the gripper, a prototype is fabricated by 3D printer. Experimental results reveal that the devised gripper owns a good constant driving force property during grasping.

Sizes and stiffness variations of actively deformable objects pose significant challenges on the design of compliant constant-force gripper. This paper presents a curved-beam based constant force compliant gripper which is composed of the constant force module, the bistable module, the preloading module and the linear guide. A curved-beam constant force mechanism is designed to generate constant force output, the non-constant force motion range of which is further eliminated via curved-based bistable mechanism and preloading module. After a formulation to find the optimal gripper configuration, the design is verified through comparison with simulation results. Finally, a prototype of the proposed gripper is tested to demonstrate its grasping capacity.

This paper presents the design and analysis of a new compliant constant-force gripper based on compound constant-force mechanism. The constant-force property can reduce the input force and prevent the object from damage without using a force feedback control. The compound constant-force mechanism contains an active and a passive constant-force structure. The active constant-force structure can reduce the input force, while the passive constant-force structure offers the safe interaction during the gripping operation. To evaluate the performance of the compound constant-force mechanism, analytical modeling is carried out, which is verified by conducting finite element analysis (FEA) simulation study. Results demonstrate the promising performance of the proposed mechanism design.