Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

This paper reports an electrostatic microelectromechanical systems (MEMS) gripper with an integrated capacitive force sensor. The sensitivity is more than three orders of magnitude higher than other monolithically fabricated MEMS grippers with force feedback. This force sensing resolution provides feedback in the range of the forces that dominate the micromanipulation process. A MEMS ultrasonic device is described for aligning microobjects suspended in water using ultrasonic fields. The alignment of the particles is of a sufficient accuracy that the microgripper must only return to a fixed position in order to pick up particles less than 100 mum in diameter. The concept is also demonstrated with HeLa cells, thus providing a useful tool in biological research and cell assays

Monolithically Fabricated Microgripper With Integrated Force Sensor for Manipulating Microobjects and Biological Cells Aligned in an Ultrasonic Field

As mechanical end-effectors, microgrippers enable the pick–transport–place of micrometer-sized objects, such as manipulation and positioning of biological cells in an aqueous environment. This paper reports on a monolithic MEMS-based microgripper with integrated force feedback along two axes and presents the first demonstration of force- controlled micro-grasping at the nanonewton force level. The system manipulates highly deformable biomaterials (porcine interstitial cells) in an aqueous environment using a microgripper that integrates a V-beam electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5 nN) and the other for gripping force measurements (force resolution: 19.9 nN). The MEMS-based microgripper and the force control system experimentally demonstrate the capability of rapid contact detection and reliable force-controlled micrograsping to accommodate variations in size and mechanical properties of objects with a high reproducibility.

https://iopscience.iop.org/article/10.1088/0960-1317/18/5/055013/pdf

Nanonewton force-controlled manipulation of biological cells using a monolithic MEMS microgripper with two-axis force feedback

Mobile sub-millimeter micro-robots have demonstrated untethered motion and transport of cargo in remote, confined or enclosed environments. However, limited by simple design and actuation, they lack remotely-actuated on-board mechanisms required to perform complex tasks such as object assembly. A flexible patterned magnetic material which allows internal actuation, resulting in a mobile micro-gripper which is driven and actuated by magnetic fields, is introduced here. By remotely controlling the magnetization direction of each micro-gripper arm, a gripping motion which can be combined with locomotion for precise transport, orientation, and programmable three-dimensional assembly of micro-parts in remote environments is demonstrated. This allows the creation of out-of-plane 3D structures and mechanisms made from several building blocks. Using multiple magnetic materials in each micro-gripper, the addressable actuation of gripper teams for parallel, distributed operation is also demonstrated. These mobile micro-grippers can potentially be applied to 3D assembly of heterogeneous meta-materials, construction of medical devices inside the human body, the study of biological systems in micro-fluidic channels, 3D micro-device prototyping or desktop micro-factories.

Three-Dimensional Programmable Assembly by Untethered Magnetic Robotic Micro-Grippers

Flexure-based micropositioning systems with a large workspace are attractive for a variety of precision engineering applications. In this paper, a new idea of multistage compound parallelogram flexure is proposed for the mechanism design of a novel parallel-kinematic XY micropositioning system, which has a motion range larger than 10 mm along with a compact structure. The established quantitative models and the stage performances are validated by conducting finite-element analysis (FEA) and experimental studies. Moreover, an enhanced model-predictive control (EMPC) is presented for positioning control of the system, which has a nonminimum-phase plant. It is shown that the EMPC is capable of producing a low magnitude of output tracking error by imposing an appropriate suppression on the control effort. Simulation and experimental studies reveal that the EMPC scheme outperforms the conventional proportional-integral-derivative (PID) and MPC methods in terms of transient response speed and steady-state accuracy. The idea that is presented in this paper is extendable to design and control of other micro-/nanopositioning systems with either minimum- or nonminimum-phase plants.

New Flexure Parallel-Kinematic Micropositioning System With Large Workspace

This paper presents the analysis, design, and characterization of a superelastic alloy (NiTi) microgripper with integrated electromagnetic actuators and piezoelectric force sensors. The microgripper, fabricated by electro-discharge machining, features force sensing capability, large force output, and large displacements to accommodate objects of various sizes. The design parameters for the embedded electromagnetic actuators were selected on the basis of finite element sensitivity analysis. In order to make the microgripper capable of resolving gripping forces, piezoelectric force sensors were fabricated and integrated into the microgripper. The performance of the microgripper, the integrated force sensors, and the electromagnetic actuators was experimentally evaluated. A satisfactory match between experimental results and finite element simulations was obtained. Furthermore, comparison studies demonstrated that the superelastic alloy (NiTi) microgripper was capable of producing larger displacement than a stainless steel microgripper. Finally, experimental results of optical fiber alignment and the manipulation of tiny biological tissues with the superelastic microgripper were presented.

https://iopscience.iop.org/article/10.1088/0964-1726/14/6/019/pdf

A superelastic alloy microgripper with embedded electromagnetic actuators and piezoelectric force sensors: a numerical and experimental study

The precision positioning system requires robust structural design to obtain enough bandwidth and efficient magnetic circuit to have fast access time. In this paper, the 3-axis nano stage was proposed and dynamic characteristics was improved by design of experiments (DOE) based on specifications of our precision positioning device. Finally, it was checked that the designed actuator had the proper dynamic characteristics through dynamic experiments.

Development of 3-axis nano stage for precision positioning in lithography system

This paper presents a superelastic alloy microgripper with integrated electromagnetic actuators and piezoelectric sensors. The design parameters for electromagnetic actuators in the microgripper are selected based on the sensitivity analysis using FEM analysis. For integration of miniature force sensors in the microgripper, the sensor design based on the piezoelectric polymer PVDF film and fabrication process are also presented. Electro discharge machining technology is employed to fabricate the microgripper structure made of superelastic NiTi alloy. The experimental setup is implemented to evaluate the performance of the fabricated force sensors and electromagnetic actuators integrated into the microgripper. Finally, results of finite element computer simulations for electromagnetic actuators and piezoelectric polymer sensors are compared with experimental results.

A superelastic alloy microgripper with embedded electromagnetic actuators and piezoelectric sensors

Development of 3-axis Nano Stage for High Precision Positioning System

The precision positioning system requires robust design to obtain enough bandwidth. Therefore, the subresonance occurred by the disaccord of the force center and the mass center should be oppressed. It is necessary to move the flexible mode to a higher frequency. In this paper, the 3-axis nano stage was proposed and dynamic characteristics was improved by design of experiments (DOE).

Moon Gu Lee

Papers

A superelastic alloy microgripper with embedded electromagnetic actuators and piezoelectric force sensors: a numerical and experimental study

Development of 3-axis nano stage for precision positioning in lithography system

A superelastic alloy microgripper with embedded electromagnetic actuators and piezoelectric sensors

Development of 3-axis Nano Stage for High Precision Positioning System

Analysis and improvement of dynamic characteristic of 3-axis nano stage