Gripper Performance Research Articles

Task and Context Sensitive Gripper Design Learning Using Dynamic Grasp Simulation

In this work, we present a generic approach to optimize the design of a parametrized robot gripper including both selected gripper mechanism parameters, and parameters of the finger geometry. We suggest six gripper quality indices that indicate different aspects of the performance of a gripper given a CAD model of an object and a task description. These quality indices are then used to learn task-specific finger designs based on dynamic simulation. We demonstrate our gripper optimization on a parallel finger type gripper described by twelve parameters. We furthermore present a parametrization of the grasping task and context, which is essential as an input to the computation of gripper performance. We exemplify important aspects of the indices by looking at their performance on subsets of the parameter space by discussing the decoupling of parameters and show optimization results for two use cases for different task contexts. We provide a qualitative evaluation of the obtained results based on existing design guidelines and our engineering experience. In addition, we show that with our method we achieve superior alignment properties compared to a naive approach with a cutout based on the “inverse of an object”. Furthermore, we provide an experimental evaluation of our proposed method by verifying the simulated grasp outcomes through a real-world experiment.

Design and Control of a Novel Compliant Constant-Force Gripper Based on Buckled Fixed-Guided Beams

This paper presents the design and control of a novel gripper device with a passive type of compliant constant-force mechanism. The function of constant-force output is achieved by using the combination of a positive-stiffness and a negative-stiffness mechanism. The negative stiffness is generated by a bistable buckled fixed-guided beam. Conventionally, when gripping a target-object using a high-stiffness gripper, both the displacement control and force control are required to prevent the damage of the object. The uniqueness of the developed constant-force gripper is that it can eliminate the dependence on force control while keeping the force constant via its mechanical structure. The gripper performance is evaluated by the established analytical model and nonlinear finite-element analysis, and validated through experimental study on a fabricated prototype. To achieve a precise position output of the gripper jaw, a discrete-time variable structure control strategy based on a nonswitching type of reaching law is realized. The effectiveness of the gripper system is verified by conducting experimental studies on grasp-hold-release operations of a micro copper wire.

DESIGN AND ANALYSIS OF FLC AND FEEDBACK CONTROL FOR THREE FINGER GRIPPER SYSTEM

This paper presents the fuzzy logic design and control for three finger gripper system to grasp an object. Two objectives are mainly considered in this work, which are the analysis of different membership types and the gripper performance with feedback and without feedback control to support current research findings. The comparison is also including different number of rules analysis as well as the fuzzy membership types. The simulation and analysis are carried by using MATLAB Simulink and SimMechanics toolboxes to analyze the system performance. The result shows that the gripper system with trapezoidal memberships achieved faster response and good grasp. Besides that, the proposed system with feedback has produced the best result to grasp the object with suitable torques and angles in comparison to the non-feedback gripper system.

A Bioinspired Soft Robotic Gripper for Adaptable and Effective Grasping

Abstract The present article shows the development of a gripper for general purposes with grasping and holding capabilities enabled by a simple control scheme. This objective has been reached exploiting the combination of soft materials, underactuated mechanisms, and a bioinspired design. The development of the soft gripper will be explained by reporting the results obtained on three different and sequential versions. The devices are here presented in their main components, underlining the anthropomorphic approach used in the design of the fingers. The used actuation mechanism is based on the control of a single cable tension, which guarantees a grasping adaptable to objects of different shape. Manipulation capability and grasping force have been tested, in order to extract a quantitative comparative analysis between the three proposed devices. The main factor that influences the improvement of the gripper performance results to be represented by the suitable combination of material with the right mechani...

Substructure compliance matrix model of planar branched flexure-hinge mechanisms: Design, testing and characterization of a gripper

This paper proposes an analytical compliance-based matrix method to model the quasi-static, small-displacement response of planar branched flexure-hinge over-constrained mechanisms. It studies structurally- and kinematically-branched flexible mechanisms comprising several chains that are connected in complex series-parallel configurations and that are acted upon by multiple external/reaction loads. These architectures are substructured or decomposed into simpler chains whose compliances are evaluated from known individual segment compliances. The substructured-chain compliances are subsequently combined with external loads to solve for unknown displacements and reactions and to further evaluate parameters relevant to the mechanism behavior. The method is applied to the design and analysis of a novel displacement-amplified gripper with right circularly corner-filleted flexure hinges. The mechanism's mechanical amplification, stiffness, and grip force are evaluated when either full or partial compliance (flexure-based only) is assumed. The analytical model predictions are confirmed by finite element analysis and by experimental testing of a proof-of-concept prototype. Subsequent analytical-model simulation highlights the relationships between the main geometric parameters and the gripper's performance qualifiers.

Single active finger IPMC microgripper

This paper presents a new design for a single active finger ionic polymer metal composite (IPMC) microgripper. This design has one stationary finger and one actuating finger. The gripper is tested in comparison with a two fingered gripper (2FG) on its ability to perform pick and place operations. The grippers each use IPMC strips in three widths: 1.25 mm, 2.5 mm and 5.0 mm. The single fingered gripper shows success rates of 86.2%, 89.2%, and 75% respectively versus 78.5%, 93.9% and 75% for a 2FG. The single fingered gripper performance is nearly equivalent to that of a 2FG. Even though a single finger produces half the force, its ability to carry objects is as good as or better than a 2FG. In addition, the stationary finger is considerably stiffer than an active IPMC finger, which helps in positional accuracy. Using half the IPMC, the single fingered gripper is the economical choice.

Design and fuzzy control of a robotic gripper for efficient strawberry harvesting

SUMMARYStrawberry is a very delicate fruit that requires special treatment during harvesting. A hierarchical control scheme is proposed based on a fuzzy controller for the force regulation of the gripper and proper grasping criteria, that can detect misplaced strawberries on the gripper or uneven distribution of forces. The design of the gripper and the controller are based on conducted experiments to measure the maximum gripping force and the required detachment force under a variety of detachment techniques. It is demonstrated that the hand motion for detaching the fruit from the stem has a significant role in the process because it can reduce the required force. By analysing those results a robotic gripper with pressure profile sensors is developed that demonstrates an efficiency comparable to the human hand for strawberry grasping. The designed gripper and fuzzy controller performance is tested with a considerable number of fresh fruits to demonstrate the effectiveness to the uncertainties of strawberry grasping.

Deriving and analyzing the effective parameters in microgrippers performance

The microgripper is a Micro-Electro-Mechanical System (MEMS) with the ability to handle and manipulate micron or sub micron objects precisely. They have many applications in micro assembly, biology, tissue engineering and so on. In this paper, the effective parameters on the performance and designing of the microgrippers are derived by reviewing and comparing their different types. These parameters are: material specification, displacement amplification factor, gripping range and stroke, jaw motion characteristic, normally open and normally closed gripper, ideal shape of tips, aspect ratio, number of degree of freedom and micro actuator specifications. These parameters are introduced and their influences on gripper performance are studied. Knowing all the effective parameters and analyzing the effect of each parameter on micro gripper performance is the first step towards design of new optimized microgrippers. Finally, an overall algorithm to design the microgripper is proposed.

A new design of piezoelectric driven compliant-based microgripper for micromanipulation

This paper describes the development of a microgripper mechanism capable of delivering high precision and fidelity manipulation of micro objects. The mechanism adopts a flexure-based concept on its joints to address the inherent nonlinearities associated with the application of conventional rigid hinges. A combination of two modeling techniques namely Pseudo Rigid Body Model (PRBM) and Finite Element Analysis (FEA) was implemented to expedite the prototyping procedure which leads to the establishment of high performance mechanism. A wire Electro Discharge Machining (EDM) technique was utilized to fabricate the monolithic structure of the gripper mechanism. Experimental studies were conducted on the model prototype to obtain various correlations governing the gripper performance as well as for model verification. The experimental results demonstrate a high level of integrity in comparison to the computational analysis. A high amplification characteristic and maximum stroke of 100 μm can be achieved.

Development of novel hybrid flexure-based microgrippers for precision micro-object manipulation

This paper describes the process of developing a microgripper that is capable of high precision and fidelity manipulation of micro-objects. The design adopts the concept of flexure-based hinges on its joints to provide the rotational motion, thus eliminating the inherent nonlinearities associated with the application of conventional rigid hinges. A combination of two modeling techniques, namely, pseudorigid body model and finite element analysis was utilized to expedite the prototyping procedure, which leads to the establishment of a high performance mechanism. A new hybrid compliant structure integrating cantilever beam and flexural hinge configurations within microgripper mechanism mainframe has been developed. This concept provides a novel approach to harness the advantages within each individual configuration while mutually compensating the limitations inherent between them. A wire electrodischarge machining technique was utilized to fabricate the gripper out of high grade aluminum alloy (Al 7075T6). Experimental studies were conducted on the model to obtain various correlations governing the gripper performance as well as for model verification. The experimental results demonstrate high level of compliance in comparison to the computational results. A high amplification characteristic and maximum achievable stroke of 100 microm can be achieved.

A self-centering electrostatic microgripper

Automated microassembly of micro hybrid devices is one fundamental step to reduce their high cost. Often, microassembly deals with fragile and wear-sensitive microparts that must be accurately grasped, positioned, and released or fastened in stable positions. The requirements of reliable, flexible, and fast assembly devices are other important characteristics to be achieved. This paper deals with the design of an electrostatic gripper that can grasp standard microcomponents and delicate mini and micro parts alike. The aim of this work is to theoretically and experimentally demonstrate the good performance of a self-centering gripper based on electrostatic forces. This paper extends previous works concerning electrostatic handling by adding new theoretical and FEM models, further tests, and new interpretations of the gripper’s grasping and centering capabilities. The design of the gripper is justified and supported by theoretical considerations. To better evaluate the generated force and the influences of the component on the gripper performance, FEM models are presented. Experiments concerning both grasping and releasing of mini and micro parts of different material shapes (spheres, cylinders, etc.) and dimensions (between 0.3 and 1 mm) have been performed, and quantitative measurements are reported. For industrial applications, the reliability of the grasping phase is close to 100%, the centering capability in grasping is appealing, and even if some centering errors remain, the transparency of the gripper allows the use of an eye-on-hand camera that could eliminate them during the releasing phase.

Using piezoelectric technology to improve servo gripper performance in mini‐ and microassembly

PurposeAims to research the possibilities of using piezoelectric technology to improve accuracy and other characteristics of parallel servo grippers.Design/methodology/approachThe paper presents in detail two different kinds of developed two‐fingered servo grippers based on piezoelectric technology with parallel moving mechanics. The first gripper is based on standing wave ultrasonic motors. The other gripper is a traditional gripper, the characteristics of which have been improved with integrated piezoelectric stack actuators. Both servo grippers have been tested and the test results and experiences are introduced in the paper.FindingsIt is possible to improve the accuracy and characteristics of a parallel servo gripper with piezoelectric technology.Research limitations/implicationsIn the future it is necessary to concentrate on the mechanical design of gripper bodies and the fingers. Grasping force feedback signal should be even more linear and noiseless.Practical implicationsPiezoelectric stack actuator's limited displacement is a problem in many practical applications when elastic or rough surface parts are handled. When integrated piezoelectric stacks are used with servo grippers, it is very important to focus on gripper's mechanical design and especially on the mechanical rigidity for getting the best possible results.Originality/valueFurther developed versions of these servo grippers can be used in high accuracy industry applications instead of traditional servo gripper technologies.

Grasping analysis for automated assembly based on a combination of gripping models and qualitative reasoning

The work proposes a knowledge reasoning system for grasping analysis in terms of gripping models and qualitative reasoning. A matrix representation of object gripping attributes, aimed at establishing a correspondence to the gripper structure and performance, is developed. Use of possible decision-making based on incomplete information of object characteristics and gripper potential actions is included. The use of the concept of imitating human-based expert systems to model events and predict physical system actions with no precise numerical data is incorporated. Finally, a generic gripper developed to validate the proposed approach is discussed.