Due to the trend of miniaturization of devices, micromanipulation has been a hot topic in the last two decades. Unlike the macro world, the micro object is easy to be damaged if the contact force is not reliably detected and controlled. Hence, micro-force sensing is of great importance in micromanipulation, microassembly, medical applications, biomedical applications, materials science, dimension measurements and MEMS/NEMS for protecting micro-parts and micro-gripper from being damaged and ensuring the success of the manipulation process. This paper presents a survey of the recent methods of micro-force sensing. The working principle, detection accuracy, advantage and disadvantage of seven widely used force sensing methods are presented. Typical applications of each method in micro-assembly and micromanipulation are discussed. In addition, the comparisons among different kinds of force sensing approaches have been addressed. Moreover, another five promising micro-force sensing methods, which are confined to special component measurements or not widely used, are briefly introduced. Furthermore, two popular types of commercial micro-force sensors are listed to provide a guideline of selection for a specific application. The presented state-of-the-art overview is helpful to those engaged in micro-force sensing area to know the recent development and research tendency on micro-force sensing.

An overview of micro-force sensing techniques

This paper is concerned with grasping biological cells in aqueous medium with miniature grippers that can also help estimate forces using vision-based displacement measurement and computation. We present the design, fabrication, and testing of three single-piece, compliant miniature grippers with parallel and angular jaw motions. Two grippers were designed using experience and intuition, while the third one was designed using topology optimization with implicit manufacturing constraints. These grippers were fabricated using different manufacturing techniques using spring steel and polydimethylsiloxane (PDMS). The grippers also serve the purpose of a force sensor. Toward this, we present a vision-based force-sensing technique by solving Cauchy's problem in elasticity using an improved algorithm. We validated this technique at the macroscale, where there was an independent method to estimate the force. In this study, the gripper was used to hold a yeast ball and a zebrafish egg cell of less than 1 mm in diameter. The forces involved were estimated to be about 30 and 10 mN for the yeast ball and the zebrafish egg cell, respectively.

Miniature Compliant Grippers With Vision-Based Force Sensing

Microfluidic Transport and Micro-scale Flow Physics: An Overview.- Mathematical Modeling of Electrokinetic Effects in Micro and Nano Fluidics.- Microscale Transport Processes and Interfacial Force Field Characterization in Micro-cooling Devices.- Bio-Microfluidics: Overview.- Perspectives of Micro and Nanofabrication of Carbon for Electrochemical and Microfluidic Applications.- Mechanical Micromanufacturing: An Overview.- Bio-Inspired Adhesion and Adhesives: Controlling Adhesion by Micro-Nano Structuring of Soft Surfaces.- Molecular Simulation: Can it Help in the Development of Micro and Nano Devices?.- Fabrication of Spring Steel and PDMS Grippers for the Micromanipulation of Biological Cells.

Microfluidics and microfabrication

Relaxation procedures for an iterative MFS algorithm for the stable reconstruction of elastic fields from Cauchy data in two-dimensional isotropic linear elasticity

For structural health monitoring, estimating the external load is a typical ill-posed problem but significant. Because with the external force and the structural finite element model, any required ...

Structural deformation reconstruction by the Penrose–Moore pseudo-inverse and singular value decomposition–estimated equivalent force:

This Study is concerned with the accurate computation of the unknown forces applied on the boundary of an elastic body using its measured displacement data with noise. Vision-based minimally intrusive force-sensing using elastically deformable grasping tools is the motivation for undertaking this problem. Since this problem involves incomplete and inconsistent displacement/force of ail elastic body, it leads to an ill-posed problem known as Cauchy's problem in elasticity. Vision-based displacement measurement necessitates large displacements of the elastic body for reasonable accuracy. Therefore, We use geometrically non-linear modelling of the elastic body, which was not considered by others who attempted to solve Cauchy's elasticity problem before. We present two methods to solve the problem. The first method uses the pseudo-inverse of an over-constrained system of equations. This method is shown to be not effective when the noise in the measured displacement data is high. We attribute this to the appearance of spurious forces at regions where there should not be any forces. The second method focuses on minimizing the spurious forces by varying the measured displacements within the known accuracy of the measurement technique. Both continuum and frame elements are used in the finite element modelling of the elastic bodies considered in the numerical examples. The performance of the two methods is compared using seven numerical examples, all of which show that the second method estimates the forces with an error that is not more than the noise in the measured displacements. An experiment was also conducted to demonstrate the effectiveness of the second method in accurately estimating the applied forces.

On computing the forces from the noisy displacement data of an elastic body

A biological cell is considered and studied as a mechanical entity today with important implications in diagnostics and therapeutics. This article describes the opportunities and challenges in using mechanical grippers in manipulating and characterizing isolated biological cells and embryos. Direct mechanical manipulation of cells has some advantages over a wide variety of techniques used in the study of cell-mechanics. Hence, we begin with a brief overview of currently used techniques and then describe the gripper-based cell-manipulation. Five aspects concerning the miniature grippers for cells are addressed here: design, materials, fabrication, force-sensing, and actuation. It is shown that systematic topology and shape optimization techniques help in designing the stiffness of the grippers to match that of the cells. Materials considered here are metals and polymers rather than just silicon. This choice of material warrants new manufacturing techniques at the meso (100 μm to cm) scale. While economic fabrication without the expensive overhead of silicon-based fabrication is the motivating factor for developing meso-scale manufacturing techniques for metals and polymers, we argue here that there are actually some other advantages in terms of functionality and performance. They arise in the context of actuating the gripper in cell’s native aqueous environment and sensing the forces exerted on the cell. We describe here a minimally intrusive force-sensing technique that does not need any specialized sensor other than the gripper itself. All of the above are made possible by compliant mechanisms, which are simply elastically deformable structures. They can be designed systematically to specifications; made with any flexible material; manufactured at any size; actuated in many ways and easily; and used as sensors. The last aspect, the sensing, needs computation as it uses the visually measured deformations to deduce the forces. Two inverse problems in elasticity are mentioned in this regard. While the first inverse problem helps in estimating forces, the second one helps in estimating the inhomogeneous mechanical properties inside the cell. It is argued that this requires dexterous manipulation of cells—a capability not usually shared by other cell-manipulation techniques.

Fabrication of Spring Steel and PDMS Grippers for the Micromanipulation of Biological Cells

We consider an inverse elasticity problem in which forces and displacements are known on the boundary and the material property distribution inside the body is to be found. In other words, we need to estimate the distribution of constitutive properties using the finite boundary data sets. Uniqueness of the solution to this problem is proved in the literature only under certain assumptions for a given complete Dirichlet-to-Neumann map. Another complication in the numerical solution of this problem is that the number of boundary data sets needed to establish uniqueness is not known even under the restricted cases where uniqueness is proved theoretically. In this paper, we present a numerical technique that can assess the sufficiency of given boundary data sets by computing the rank of a sensitivity matrix that arises in the Gauss-Newton method used to solve the problem. Numerical experiments are presented to illustrate the method.

A numerical approach to determine the sufficiency of given boundary data sets for uniquely estimating interior elastic properties

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On computing the forces from the noisy displacement data of an elastic body

Fabrication of Spring Steel and PDMS Grippers for the Micromanipulation of Biological Cells

A numerical approach to determine the sufficiency of given boundary data sets for uniquely estimating interior elastic properties