Planning and control for microassembly of structures composed of stress-engineered MEMS microrobots

We present control strategies that implement planar microassembly using groups of stress-engineered MEMS microrobots (MicroStressBots) controlled through a single global control signal. The global control signal couples the motion of the devices, causing the system to be highly underactuated. In order for the robots to assemble into arbitrary planar shapes despite the high degree of underactuation, it is desirable that each robot be independently maneuverable (independently controllable). To achieve independent control, we fabricated robots that behave (move) differently from one another in response to the same global control signal. We harnessed this differentiation to develop assembly control strategies, where the assembly goal is a desired geometric shape that can be obtained by connecting the chassis of individual robots. We derived and experimentally tested assembly plans that command some of the robots to make progress toward the goal, while other robots are constrained to remain in small circular trajectories (orbits) until it is their turn to move into the goal shape. Our control strategies were tested on systems of fabricated MicroStressBots. The robots are 240–280 µm × 60 µm × 7–20 µm in size and move simultaneously within a single operating environment. We demonstrated the feasibility of our control scheme by accurately assembling five different types of planar microstructures

A Steerable, Untethered, 250x60 micron MEMS Mobile Micro-Robot

We present a steerable, electrostatic, untethered, MEMS micro-robot, with dimensions of 60 µm by 250 µm by 10 µm. This micro-robot is 1 to 2 orders of magnitude smaller in size than previous micro-robotic systems. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator. These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate and without constraining rails or tethers. Control and power delivery waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace (the robot is globally controllable). These MEMS micro-robots demonstrate turning error of less than 3.7 °/mm during forward motion, turn with radii as small as 176 µm, and achieve speeds of over 200 µm/sec, with an average step size of 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths

REDUCING MODEL CREATION CYCLE TIME by Automated Conversion Of a CAD AMHS Layout Design

Simulation is a popular tool for accurately estimating the performance of an automated material handling system (AMHS). Accuracy of the model is normally dependent on a detailed description of the AMHS physical system components and their coordinate positions. In this paper, a methodology is defined for automatically inputting the physical system components used to describe an AMHS within a simulation language. The method is based on data extraction from a CAD layout file of the system. Automatically generating the physical system components reduces simulation model building time and increases model accuracy

Planar Microassembly by Parallel Actuation of MEMS Microrobots (Microassembly Video)

Movie of a representative microassembly experiment using devices from species 1,3,4 and 5, recorded through an optical microscope. The robots are initially arranged along the corners of a rectangle with sides 1 by 0.9 mm. The assembly experiment is divided into three stages. During stage 1, devices 4 and 5 dock together to form the initial stable shape. In stage 2, device 3 docks with the initial stable shape, while during stage 3, device 1 docks with the stable shape, forming the final assembly

Pas de Deux avec les Microrobots (Video)

Video captured through an optical microscope, showing simultaneous control and operation of two stress-engineered microrobots. The dimensions of our microrobots are 260 x 60 x 10 micrometers; each robot consists of an unthetered scratch-drive actuator that provides forward motion, and a steering-arm actuator that controls whether the robot moves in a straight line or turns. Our stress-engineered microrobots are electrostatically powered via a global control signal transmitted to all the robots regardless of the their position and orientation within their operating environment. Hence, a single control and power-delivery signal must be used to simultaneously control all robots within the same operating environment, resulting in a highly underactuated system. Despite this high level of underactution we are able to achieve independent control of the individual microrobots by designing their steering-arms to respond to different voltage levels of the supplied control signal. This example uses nested hysteresis gaps. A hysteresis gap is the difference between the snap-down and release voltages for a steering-arm actuator. Nested hysteresis gaps allow us to set the states of the steering-arms (up or down) to any configuration. As shown in this video, all four states of the two microrobot steering-arms are used to choreograph their motion. A disadvantage of nested hysteresis gaps is that they are control-voltage bandwidth intensive, limiting the number of simultaneously-controllable devices. An alternative multi-microrobot control scheme that minimizes control-bandwidth is described in [1]