Microassembly Tasks Research Articles

Responsive Hydrogel-Based Modular Microrobots for Multi-Functional Micromanipulation.

Microrobots show great potential in biomedical applications such as drug delivery and cell manipulations. However, current microrobots are mostly fabricated as a single entity and type and the tasks they can perform are limited. In this paper, modular microrobots, with an overall size of 120 µm × 200 µm, are proposed with responsive mating components, made from stimuli-responsive hydrogels, and application specific end-effectors for microassembly tasks. The modular microrobots are fabricated based on photolithography and two-photon polymerization together or separately. Two types of modular microrobots are created based on the location of the responsive mating component. The first type of modular microrobot has a mating component that can shrink upon stimulation, while the second type has a double bilayer structure that can realize an open and close motion. The exchange of end-effectors with an identical actuation base is demonstrated for both types of microrobots. Finally, different manipulation tasks are performed with different types ofend-effectors.

Novel Coil Array Design and Modeling for Independent Control of Multiple Magnetic Microrobots

The independent control of microrobot swarms is a major challenge in the field of micro/nano manipulation. In this paper, a new localized magnetic field generating system is presented that can be used for the independent control of multiple magnetic microrobots. Such a system will allow for cooperative or parallel microassembly tasks with teams of magnetic microrobots. Firstly, the performance of the novel circular microcoil is modeled by analyzing the effect of input current to study the magnetic field distribution characteristics in the workspace, which is validated by finite element analysis and simulation; then, an actuation and control strategy of microrobots for microcoil array is proposed. Meanwhile, the independent closed-loop control of the microrobot is realized based on visual feedback; finally, an experimental platform for the microcoil actuation system is built to validate the newly designed structure. The results show that the microrobot can move flexibly and accurately with the tracking error within 0.444mm. At the same time, the system is capable of independently controlling multiple microrobots and holds great potential in performing micromanipulation tasks.

Cooperative Self-Assembled Magnetic Micropaddles at Liquid Surfaces.

Cooperative controls of magnetic microswimmers are desired for complex micromanipulation and microassembly tasks. Self-assembled magnetic micropaddles as microswimmers that can locomote freely and cooperate at liquid surfaces are proposed inspired by the paddling motion. The micropaddles are self-assembled with metallic disks under a rotating magnetic field, and they are endowed with controlled propulsion in the precessing field. The micropaddles can locomote freely with a maximum speed of approximately 3.3 mm/s and manipulate objects at the liquid surface. It is found that the micropaddles reverse moving directions at high frequencies and that those with different lengths can locomote in opposite directions under the same precessing magnetic field. Based on the distinctive motion properties, not only could several micropaddles combine into the longer ones but a single micropaddle could also be disassembled into two cooperative partners. Assemblies of different parts based on their cooperation are realized in this study, which is challenging for other types of magnetic microswimmers. Micropaddles with adjustable length, flexible locomotion, and cooperative capability present a promising avenue for various micromanipulation applications.

Design of flexure-based modular architecture micro-positioning stage

As the current trend in numerous industrial domains is to miniaturise products, micro-positioning stage(MPS) capable of performing micro-manipulation and micro-assembly tasks with sub-micrometer or nanometer precision is playing an increasing important role in these fields. In addition, well performances and low cost are two emergency issues need to be addressed for widely using flexure-based MPSs. However, the design and fabrication process for MPSs at present are costly both in time and money. Especially, the designed configurations are tailored to a specific application without flexibility. Thus, the purpose of this paper is to introduce a design of precision flexure-based reconfigurable MPSs which provide better flexibility and functionality and allows to reduce the time to market significantly. To begin with, performance requirements and benefits for reconfigurable MPSs are introduced. Then, some typical modules and their functions are introduced in detail. Finally, some selective stages assembled with function modules are proposed as case studies, for the purpose of validating the benefits of reconfigurable MPSs.

Local Magnetic Field Design and Characterization for Independent Closed-Loop Control of Multiple Mobile Microrobots

We present a new localized magnetic field generating system consisting of microcoils in two different layers of a printed circuit board that can be used for the independent control of multiple magnetic microrobots. Such a system will allow for cooperative or parallel microassembly tasks with teams of magnetic microrobots. In this article, we have modeled and characterized the performance of the microcoils in the workspace by analyzing the effects of input current and substrate layer position. The interactions between the magnetic microrobots that affect their motion in the workspace was also studied. The local magnetic field generates sufficient forces to enable the closed-loop control of multiple microrobots in the workspace. A new microrobot design is then presented that enables orientation control of a magnetic microrobot when actuated by local magnetic fields. An overview of the design is presented first and then it is experimentally validated. Finally, sample micromanipulation tasks are demonstrated using the new microrobot design, showcasing its improved manipulation capabilities.

Design and Control of a Piezoelectric-Driven Microgripper Perceiving Displacement and Gripping Force.

A piezoelectric-driven microgripper with three-stage amplification was designed, which is able to perceive the tip displacement and gripping force. The key structure parameters of the microgripper were determined by finite element optimization and its theoretical amplification ratio was derived. The tracking experiments of the tip displacement and gripping force were conducted with a PID controller. It is shown that the standard deviation of tracking error of the tip displacement is less than 0.2 μm and the gripping force is 0.35 mN under a closed-loop control. It would provide some references for realizing high-precision microassembly tasks with the designed microgripper which can control the displacement and gripping force accurately.

Direct Drop-on-Demand Printing of Molten Solder Bumps on ENIG Finishing at Ambient Conditions Through StarJet Technology

In this paper, we report on a detailed experimental study carried out with the StarJet technology to investigate the mechanical adhesion properties of directly printed solder bumps on electroless nickel immersion gold (ENIG) plated PCB boards. The aim of this study is to determine the maximum bond strength achievable by this method and to find suitable printing parameters that allow for the production of reliable and consistent solder bumps by non-contact printing of molten solder (type SAC305). Molten solder droplets of about $250~\mu \text{m}$ diameter were printed at melt temperatures between 250 and 400 °C onto ENIG surfaces kept at temperatures in the range of 100 to 200 °C. Using shear force tests, the adhesion of the printed bumps was investigated as a function of the main process parameters: 1. printhead temperature, 2. substrate temperature, and 3. substrate preheating time. The formation of an intermetallic compound (IMC) between the solder and the ENIG was confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) measurements. As a result of the comprehensive experimental parameter study, suitable printing parameters for establishing bond strengths corresponding to maximum shear force values of 3000 to 4000 mN could be found, i.e. high printhead temperature of 400 °C, short preheating and time of < 2 min, and substrate heating at 180 °C The use of flux was found to slightly improve the bond strength and to improve the consistency of the printing results for extended operation times. The achieved high bond strength and the reasonable reproducibility of the printing results qualify the StarJet technology for further investigations regarding applications in the field of direct soldering of microelectronic chips and devices to PCB boards as well as other micro-assembly tasks in the future.

Towards Functional Mobile Microrobotic Systems

This paper presents our work over the last decade in developing functional microrobotic systems, which include wireless actuation of microrobots to traverse complex surfaces, addition of sensing capabilities, and independent actuation of swarms of microrobots. We will discuss our work on the design, fabrication, and testing of a number of different mobile microrobots that are able to achieve these goals. These microrobots include the microscale magnetorestrictive asymmetric bimorph microrobot ( μ MAB), our first attempt at magnetic actuation in the microscale; the microscale tumbling microrobot ( μ TUM), our microrobot capable of traversing complex surfaces in both wet and dry conditions; and the micro-force sensing magnetic microrobot ( μ FSMM), which is capable of real-time micro-force sensing feedback to the user as well as intuitive wireless actuation. Additionally, we will present our latest results on using local magnetic field actuation for independent control of multiple microrobots in the same workspace for microassembly tasks.

C2F: Coarse-to-Fine Vision Control System for Automated Microassembly

Introduction:In this paper, authors present the development of a completely automated system to perform 3D micromanipulation and microassembly tasks. The microassembly workstation consists of a 3 degree-of-freedom (DOF) MM3A® micromanipulator arm attached to a microgripper, two 2 DOF PI® linear micromotion stages, one optical microscope coupled with a CCD image sensor, and two CMOS cameras for coarse vision.Methods:The whole control strategy is subdivided into sequential vision based routines: manipulator detection and coarse alignment, autofocus and fine alignment of microgripper, target object detection, and performing the required assembly tasks. A section comparing various objective functions useful in the autofocusing regime is included.Results:The control system is built entirely in the image frame, eliminating the need for system calibration, hence improving speed of operation. A micromanipulation experiment performing pick-and-place of a micromesh is illustrated.Conclusion:This demonstrates a three-fold reduction in setup and run time for fundamental micromanipulation tasks, as compared to manual operation. Accuracy, repeatability and reliability of the programmed system is analyzed.

A Microforce-Sensing Mobile Microrobot for Automated Micromanipulation Tasks

This paper presents a microforce-sensing mobile microrobot ( $\mu $ FSMM) for use in automated micromanipulation tasks. The design consists of a planar vision-based microforce sensor end-effector, while the microrobot body is made of chemically etched nickel that is driven by an exterior magnetic field. With a known stiffness, the manipulation forces can be determined from observing the deformation of the end-effector through a camera attached to an optical microscope. After analyzing and calibrating the stiffness of a micromachined prototype, the mobility and in situ force-sensing capabilities are verified through real-time, closed loop, force controlled manipulation tests with automated path planning and navigation. The calibrated stiffness of the microforce sensor end-effectors fabricated is on the order of 10−3 N/m. The online (real time) force-sensing resolution is approximately $1.5~\mu \text{N}$ . The sensing range is 0–20 $\mu \text{N}$ along the two planar directions. In automated micromanipulation experiments with a microcomponent, the $\mu $ FSMM utilizes real-time force control to apply a prescribed force of $6~\mu \text{N}$ to a desired location on a fixed microobject. Similarly, in another automated micromanipulation experiment, the $\mu $ FSMM demonstrates the use of real-time force control to limit the manipulation forces experienced by the microobject to remain below a threshold of 12 $\mu \text{N}$ . Note to Practitioners —This paper was motivated by recent interest single-cell biological micromanipulation tasks that seek to understand the role of environmental forces on the mechanics of cell development (mechanobiology) and the biological mechanisms that control such behavior (mechanotransduction). In addition, tissue engineering applications require the safe micromanipulation of single cells to desired locations in the workspace for growing tissue scaffolds. The $\mu $ FSMM presented here can be easily inserted into existing biological testbeds to use for these aforementioned applications. The designed magnetic coil system is compatible with standard inverted optical microscopes, while a digital camera for real-time image processing is already standard in these testbeds. The developed software interface can be used to prescribe automated microforce controlled manipulations of single cells and tissues in the workspace to carry out these aforementioned tasks. This paper is also suitable for carrying out general automated micromanipulation and microassembly tasks with advanced manufacturing applications.

Design of Reconfigurable Planar Micro-Positioning Stages Based on Function Modules

Micro-positioning stages, which are capable to meet the emerging industrial trend for performing various kinds of micro-manipulation and micro-assembly tasks are the crucial tools to miniaturize the products under ultra-high precision. The current main practice is to specifically tailor a monolithic positioning stage design for one kind of micro-manipulation application. However, the design and fabrication of such a specific flexure-based micro-positioning stage are expensive in both the time and financial investment. In order to increase the flexibility and functionality of micro-positioning stages, this paper proposes a novel reconfigurable planar micro-positioning stages platform based on different function modules. A functional model-based approach is developed to divide one micro-positioning stage into a set of functionally independent sub-models, which allows flexible composition resulting in an adjustable new stage. The robustness of the proposed platform is demonstrated using some typical micro-positioning stages benchmarking cases. The effectiveness of assembly using flexible function modules is verified to show the benefits of the proposed design platform for reconfigurable micro-positioning stages.

Pareto optimization-based trade-off between the visual resolvability and the intersection space of view of binocular microscopic vision system for microassembly systems

Visual resolvability and intersection space of view of a binocular microscopic vision system (MVS) in microassembly systems have influences on each other via analyzing theoretically. According to requirements of various microassembly tasks, it is an explicit problem how to find the best compromise between the visual resolvability of binocular MVS and its intersection space of view in three-dimensional space. A Pareto optimization-based method to make the trade-off between the visual resolvability and the intersection space of view of binocular MVS with relevant fixed parameters in microassembly systems is proposed. Through modeling and analyzing on the visual resolvability and intersection space of view of a binocular MVS, the topology and optical magnifications of two MVSs are considered as the key parameters to optimize its physical properties. A multiobjection optimization model based on a Pareto optimization method is formulated and used to find the Pareto optimal cure, namely the Pareto front, which represents the best trade-off between the visual resolvability and the intersection space of view of a binocular MVS. On these bases, the physical properties of a binocular MVS with structural parameters corresponding to the optimization solutions are numerically simulated. Accordingly, a binocular MVS with different parameters is established on an automatic microassembly system with a single manipulator with five degree-of-freedom and experimentally tested. The simulation and experimental results indicate that all of the optimal solutions, which locate on the Pareto front, are the best trade-off between the visual resolvability and the intersection space of view of a binocular MVS. According to the Pareto front, physical parameters of a binocular MVS can be chosen to get the optimal visual resolvability with a certain intersection space of view and vice versa.

Diamagnetically levitated Milli-robots for heterogeneous 3D assembly

In this article, we demonstrate diamagnetically levitated milli-robots performing 3D heterogeneous micro-assembly of silicon micro-machined parts and polymer microspheres. Diamagnetically levitated milli-robots, in conjunction with controlled magnetic fields from printed circuit boards, can enable very precise, low cost, high density, and an easily scalable approach to massively parallel micro-assembly. By using an eddy-current dampening layer to suppress ambient external forces, we measured an open-loop in-plane equilibrium motion repeatability of 28.6 nm rms over cm’s of travel and a total vertical range of 50–70 μm. To perform micro-assembly, light-weight end effectors and force compatible micro-processes (i.e. micro-grasping and liquid handling) were integrated with the diamagnetic levitated milli-robots. Various tele-operated micro-assembly tasks were demonstrated such as joining polymer micro-spheres, interlocking silicon micro-parts, and printing electrical interconnects. Multiple specialized milli-robots, each taking up only 31 mm2, are used to perform each individual micro-task. In the future, by developing more sophisticated milli-robots and operating many more of these milli-robots in parallel, a dense, automated, rapid milli-robot assembly may be possible.

Design and Development of a Novel Compliant Gripper With Integrated Position and Grasping/Interaction Force Sensing

This paper proposes a new compliant gripper with integrated position and force sensors dedicated to automated microassembly tasks. The uniqueness of the gripper is that it possesses a large gripping range with a bidirectional drive, and it is capable of detecting grasping force and environmental interaction forces in horizonal and vertical axes, respectively. This is enabled by a mechanism design based on a rotary flexure bearing. Moreover, a compliant mechanism with two-stage stiffness is designed to provide the force sensing with dual sensitivities and measuring ranges to accommodate the grasp of objects with different sizes and weights. Analytical models are derived to predict the grasping range, force sensing sensitivities, and ranges. These models are verified by conducting finite-element analysis simulations. A proof-of-concept prototype gripper is developed for experimental calibration and performance testing. Results reveal that the single set of strain-gauge force sensor is able to detect both grasping and interaction forces in an alternate manner. The dual-sensitivity, dual-range force sensor provides a solution to large-range gripper with finer and coarser force sensing in a small and large ranges, respectively .

Design of asymmetric flexible micro-gripper mechanism based on flexure hinges

Symmetric micro-gripper mechanism is very easy way to destroy the micro-components or parts for nonuniform force in the processing of micro-assembly. Aiming at the requirements of micro-assembly for the microtubule (diameter of 0–200 μm) components, a new type of asymmetric flexible micro-gripper mechanism based on flexure hinges was designed and studied. The asymmetric micro-gripper mechanism was driven by piezoelectric actuator, whose output displacement was amplified and transmitted by flexure hinges, and the flexible parallel four-bar mechanism was used to ensure that the micro-clamp moves and is held parallel. The displacement amplification ratio of the asymmetric flexible micro-gripper mechanism was deduced theoretically, and the finite element analysis and the experiment were also carried out to study the displacement amplification ratio in detail. The experiment results show that the displacement amplification ratio of the asymmetric flexible micro-gripper mechanism is 4.16, compared with the finite element analysis result and the theoretical calculation result; the error between them is 1.89% and 5.67%, respectively. The experiment results also show that the step-wise resolution of the micro-gripper is 7.50 μm, and the output force of the right micro-clamp was measured at 0.28 N. The asymmetric flexible micro-gripper mechanism is able to perform the micro-assembly tasks for the microtubule parts, and it is helpful to design this type of micro-gripper mechanism.

Robust Impedance Control of a Compliant Microgripper for High-Speed Position/Force Regulation

High-speed simultaneous position and contact force control is vital for microgrippers dedicated to automated high-throughput microassembly tasks. This paper presents the design and validation of a new robust impedance control for high-speed position and force regulation of a compliant gripper which is driven by a piezoelectric stack actuator. Unlike traditional position/force switching control, the proposed scheme enables a smooth transition between the free and constrained motions of the gripper. A single controller is devised to regulate both the gripper tip position and the contact force, rendering a simplification in control design. The stability of the closed-loop system in the presence of piezoelectric nonlinearities is guaranteed by a digital sliding mode impedance control algorithm. Moreover, the proposed control scheme is applicable to high-order systems, and the control algorithm simplification enables a high-speed loop rate. The high-speed control is realized by deploying the algorithm to a field-programmable gate array controller. The effectiveness of the proposed scheme is verified through experimental studies on grasp-hold-release operation of a graphite microrod. The control scheme can be extended to other microassembly systems as well.

Parametric study of a novel asymmetric micro-gripper mechanism

Aiming at the requirements of micro-assembly for the microtubule (diameter of 0-200μm) components, a new type of asymmetric flexible micro-gripper mechanism based on flexure hinges was designed and studied. The asymmetric micro-gripper mechanism was driven by piezoelectric actuator, whose output displacement was amplified and transmitted by flexure hinges. The displacement amplification ratio of the asymmetric flexible micro-gripper mechanism was deduced theoretically, and the key structure parameters were developed by the FEA (Finite Element Analysis) method. The simulation and experiment were both carried out in order to study the displacement amplification ratio in detail. The experiment results show that the displacement amplification ratio of the asymmetric flexible micro-gripper mechanism is 4.16, compared with the FEA result and the theoretical calculation result, the error between them is 1.89% and 5.67%, respectively. The experiment results also show that the step-wise resolution of the micro-gripper is 7.50μm. The asymmetric flexible micro-gripper mechanism is able to perform the micro-assembly tasks for the microtubule parts, and it is helpful to design this type of micro-gripper mechanism.

Simulation of Liquid Meniscus and Microdrop Formation of a Capillary Gripper for Microparts Transfer

Microparts transfer plays an important role in various micromanipulation and microassembly tasks. One typical way of microparts transfer is based on the pick-and-place method with a microgripper. Microparts have the potential risks to be damaged due to the local stress concentration when they are gripped and it is a great challenge to release them reliably due to adhesion forces at microscale. In this paper, a flexible and reliable pick-and-place transfer scheme with a capillary gripper is proposed and the principle of the transfer scheme is based on microdrop control. A series of simulations are also performed. For picking microparts, the simulation results show that meniscus can be adjusted by altering the interface pressure. For placing microparts, the controllable formation of microdrops shows the placing reliability. These results are helpful to further optimization and control of the proposed capillary gripper.

Precision Position/Force Interaction Control of a Piezoelectric Multimorph Microgripper for Microassembly

Precision position and force control is a critical issue for automated microassembly systems to handle micro-objects delicately. This paper presents two new approaches to regulating both position and contact force of a piezoelectric multimorph microgripper dedicated to microassembly tasks. One of the advantages of the proposed approaches lies in that they are capable of controlling the position and contact force of a gripper arm simultaneously. The methodology is easy to implement since neither a state observer nor a hysteresis model of the system is required. The first approach is a position-based sliding mode impedance control which converts the target impedance into a desired position trajectory to be tracked, and the second one is established on the basis of a proportional-integral type of sliding function of the impedance measure error. Their tracking performances are guaranteed by two devised discrete-time sliding mode control algorithms, whose stabilities in the presence of model uncertainties and disturbances are proved in theory. The effectiveness of both schemes are validated by experimental investigations on a glass microbead gripping task. Results show that both approaches are capable of accomplishing promising interaction control accuracy.

Study of Forces During Microassembly Tasks Using Two-Sensing-Fingers Grippers

In this paper, the use of a two-sensing-fingers gripper for grasping planar microparts (smaller than 0.1 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^3$</tex></formula> ) is being investigated and the force range during a microassembly sequence is estimated between 0 to 3 mN. An analytical model of their gripping forces in the presence of a lateral contact force is proposed and is compared to Finite Element Analysis. An experimental validation is performed by a proposed setup for a lateral contact force in the range of a few tens to hundreds of micronewtons. Effects of the variation of parameters like the distance of contact, the thickness of the finger, the compliance of the finger, and the preload are investigated. Design statements of microgripper and the applied force range are given in order to achieve automated microassembly tasks.