We demonstrate mass-producible, tetherless microgrippers that can be remotely triggered by temperature and chemicals under biologically relevant conditions. The microgrippers use a self-contained actuation response, obviating the need for external tethers in operation. The grippers can be actuated en masse, even while spatially separated. We used the microgrippers to perform diverse functions, such as picking up a bead on a substrate and the removal of cells from tissue embedded at the end of a capillary (an in vitro biopsy).

Tetherless thermobiochemically actuated microgrippers.

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.

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

Industry 4.0 aims at integrating machines and operators through network connections and information management. It proposes the use of a set of technologies in industry, such as data analysis, Internet of Things, cloud computing, cooperative robots, and immersive technologies. This paper presents a training system for industrial operators in assembly tasks, which takes advantage of tools such as virtual reality and process mining. First, expert workers use an immersive interface to perform assemblies according to their experience. Then, process mining algorithms are applied to obtain assembly models from event logs. Finally, trainee workers use an improved immersive interface with hints to learn the assemblies that the expert workers introduced in the system. A toy example has been developed with building blocks and tests have been performed with a set of volunteers. The results show that the proposed training system, based on process mining and virtual reality, is competitive against conventional alternatives. Furthermore, user evaluations are better in terms of mental demand, perception, learning, results, and performance.

A training system for Industry 4.0 operators in complex assemblies based on virtual reality and process mining

This paper surveys contact micromanipulation strategies that are developed to tackle the microscale-related phenomena in microassembly. Strategies are divided according to how they take account of adhesion forces. Micromanipulation refers to handling of objects that have dimensions below hundreds of micrometers with handling accuracy down to submicrometers. The line between micro- and nanomanipulation is not definite but typically the object size in nanomanipulation is considered to reach from atomic and molecular scale to hundreds of nanometers. In contact micromanipulation, the tool physically touches the manipulated objects during handling. Scaling-effect-induced adhesion forces severely complicate micromanipulation when compared to conventional macromanipulation. At microscale, the most important adhesive forces are van der Waals force, electrostatic force, and capillary force. Adhesion forces are also the reason behind the fairly low level of automation in microassembly systems. Improved success rate of micromanipulation operations requires that the special features of microscale phenomena be taken into consideration.

Contact Micromanipulation—Survey of Strategies

A Comprehensive Survey on Microgrippers Design: Mechanical Structure

This paper provides a comprehensive review of research efforts in the emerging field of micro devices assembly (MDA) as well as identifies future directions for research. The general domain dealing with both manual and automated assembly of micro devices can be referred to as MDA. The study of computer-based methods to accomplish the assembly of micron-sized parts can be described as Automated MDA (AMDA). The primary focus of this paper is to provide an overview of concepts related to MDA as well as a review of various segments of MDA research including study of the role of interactive forces at the micro level, the design of innovative gripping and assembly techniques as well as the use of information technology (IT) based approaches.

Daniel Vasquez

Papers

Assembly and manipulation of micro devices-A state of the art survey