One of the major issues enduring with micro-scale mechanics has been to design high fidelity miniature machines capable of performing complex operations. Though achieved in some proportion through conventional in-plane and out-of-plane designs, the efficacy of such micro-electromechanical systems (MEMS) structures is highly limited due to complicate fabrication and inadequate robustness. On the other hand, the use of precise robots to assemble MEMS parts of comparatively simpler design to build 3D micromechanical structures has recently emerged as a viable approach. Such modular assemblies of microscale parts typically utilize minimum energy connectors that are multifunctional, e.g., mechanical, electrical etc. The μ3is a 3D microassembly station consisting of 19 DOF arranged into 3 micromanipulators, with additional microgrippers and stereo microscope vision. The platform is capable of motion resolutions of 3nm and is small enough to be used inside of a scanning electron microscope (SEM) for nano-manipulation. In this paper we discuss how systematic identification and calibration of the station, combined with appropriate part connector designs can lead to multi-degree of freedom active MEMS robots assembled on a wafer

Microgrippers based on electrothermal actuation were designed and fabricated using the deep reactive ion etching (DRIE) process with 100mum thick silicon on insulator (SOI) wafer. The design requirements are restricted to basic manipulation tasks such as pick and place, and nonprehensile manipulation. This paper explores several electrothermal end-effectors which have been fabricated for serial and parallel microassembly. The end-effectors include three main building blocks: 1) Integrated and symmetrical actuators of V and U shapes. The symmetrical expansions on Chevron and hot arms allow combination of forward translations that amplify angular motion at the tips of a gripper. 2) A joule heating element based on a resistive V-shape electrothermal actuator. In 3D microassembly, the joining of a micropart is essentially performed by providing an integrated microheater device. 3) A force or position feedback sensing block based on self-straining or electrostatic principle. The integrated sensor can be calibrated for both position and force measurements. Serial heterogeneous assembly of meso and micro-scale objects is demonstrated using a 3D microassembly station. Black-box dynamical models for microgrippers are derived using experimentally obtained data, and performance variations due to the way the microgrippers are mounted onto the robot are discussed.

This work presents a framework of tolerance analysis of microparts in microassembly. Tolerance analysis at the micro scale has not been investigated so far even though tolerance analysis at the macro scale has extensively been investigated to improve an assembly yield. It is important to know the positional uncertainties and statistical distribution of parts before and after untethering to improve assembly yield. Positional misalignments of microparts are extracted from raw CCD images and the statistical distribution of parts variances are computed using clustering and transformation of Gaussian distribution. The distributions are not pure Gaussian in nature as might be expected. There are several location peaks found, usually centered at the fabrication location, and at the hard-stop locators.

This paper presents analytical, simulation and experimental results from a study of compliant insertion tasks in microassembly. Gripper compliance is desirable to compensate for positional errors and to prevent the breakage of a gripper during assembly tasks. An analytical model is derived to study the motion and force profiles during compliant insertion. Thermal bimorph microgrippers with a compliant tip are designed and fabricated using a silicon DRIE process, and are mounted on a precision motion stage. A series of micropeg manipulation tasks such as pick up, rotation, and insertion are successfully performed. Finally, a comb structure is integrated in the gripper to calculate insertion force by measuring the deflection of a gripper, which is essential for automated microassembly.

Highly redundant modular robots may undergo large shape changes which significantly affect the geometry and dynamics of the robot. In these motions, the shape change may induce a tipping or rolling behavior of the robot. The paper describes the dynamic modeling, locomotion planning, control and simulation of such rolling motions for the Tetrobot modular robots. The motion is described by the path profiles of controlled nodes, the tipping criteria and dynamic tipping motion and an impact-reaction model of contact with the ground. These phases of motion are described using Newton-Euler dynamic equations and the principle of conservation of angular momentum. In the paper, a two-phase planning and switching control sequence is introduced to achieve stable and reliable motion of a Tetrobot modular robot. Simulation results illustrate the tipping behavior of a tetrahedron, the dynamic contact and rolling of an icosahedral Tetrobot and dynamic control of the rolling Tetrobot. The resulting models are useful to analyze and control both intentional rolling as a new mode of mobility as well as the avoidance of unintentional tipping and rolling during task execution.

Highly redundant modular robots may undergo large shape changes which significantly affect the geometry and dynamics of the robot. In these motions, the shape change may induce a tipping or rolling behavior of the robot itself. The paper describes the dynamic modeling, control, and simulation of such rolling motions for the Tetrobot modular robots. The motion is described by the path profiles of controlled nodes, the tipping criteria and dynamic tipping motion, and an impact-reaction model of contact with the ground. These phases of motion are described using Newton-Euler dynamic equations and the principle of conservation of angular momentum. Simulation results illustrate the tipping behavior of a tetrahedron, the dynamic contact and rolling of an icosahedral Tetrobot, and dynamic control of the rolling Tetrobot. The resulting models are useful to analyze and control both intentional rolling as a new mode of mobility as well as the avoidance of unintentional tipping and rolling during task execution.

In a recent study of modular robots (2000), the authors demonstrated the feasibility of dynamic rolling motions as a novel means of locomotion. In such a system the capability of large shape change is used to induce tipping and rolling behaviors of the robot itself. However, the dynamics of the tipping motion and the contact forces that occur on impact with the ground are complex. In this paper, a two-phase planning and switching control sequence is introduced to achieve stable and reliable motion of an icosahedral Tetrobot modular robot. Simulation of the resulting rolling motions suggests that speed and direction of the rolling can be controlled, and both sustained uphill and downhill rolling motions are feasible.

This paper proposes a distributed control scheme for a highly redundant parallel Tetrobot mechanism. The architecture of the proposed distributed control is composed of processors dedicated to each module and a network used to communicate the information between the modules. Each processor computes the kinematics, dynamics and control input for the dedicated module using the subsystem dynamic model and the information communicated only from adjacent modules. The simulation results of set-point and tracking control are provided to demonstrate the feasibility of the proposed scheme and compared to centralized control. The results show that the controlled node reaches the desired position without a steady state error even though the convergence rate is slower than for the centralized scheme. To improve the problem caused by a local optimization technique, an iteration scheme of local optimization was also applied to obtain a global solution to generate the paths of uncontrolled nodes.

A distributed computation algorithm based on the virtual force method supports the computation of dynamic redundancy resolution for modular reconfigurable robotic systems. Such systems have many redundant degrees of freedom in order to meet the combined demands of strength, rigidity, workspace kinematics, reconfigurability, and fault tolerance. An efficient distributed computational scheme computes the kinematics, dynamics, and redundancy resolution for real-time application to the control of these systems. A potential function which depends only on the local information of adjacent nodes of the structure is introduced and applied to the Tetrobot modular reconfigurable system. Simulation results are provided to demonstrate the feasibility of the proposed distributed algorithms, and these results are compared to the centralized Jacobian method which requires global information.

Highly redundant parallel manipulators are gaining increased attention due to their capability to meet demands of strength, rigidity, kinematic structure, dexterity, reconfigurability, and fault tolerance. Most previous research has considered the kinematic resolution of highly redundant parallel manipulators, and the dynamic resolution of redundancy has not yet been studied for these systems. This paper presents the dynamic simulation of a highly redundant parallel manipulator called Tetrobot, a class of modular reconfigurable robotic systems. The modular concept is applied to formulate the kinematic and dynamic equations of motion. In this modular approach, kinematic and dynamic solutions are obtained for Tetrobot mechanisms by propagation through the structures. Results show that the pseudoinverse solution which minimizes the norm of acceleration may introduce stability problems, and the null space vector which avoids joint limits is required to ensure stability.