Uncalibrated Visual Servo Control of Magnetically Actuated Microrobots in a Fluid Environment

Abstract

Abstract:Microrobots have a number of potential applications for micromanipulation and assembly, but also offer challenges in power and control. This paper describes an uncalibrated vision-based control system for magnetically actuated microrobots operating untethered at the interface between two immiscible fluids. The microrobots are 20 μm thick and approximately 100-200 μm in lateral dimension. Several different robot shapes are investigated. The robots and fluid are in a 20 × 20 × 15 mm vial placed at the center of four electromagnets. Pulse width modulation of the electromagnet currents is used to control robot speed and direction. Given a desired position, a controller based on recursive least square estimation drives the microrobot to the goal without a priori knowledge of system parameters such as drag coefficients or intrinsic and extrinsic camera parameters. Results are verified experimentally using a variety of microrobot shapes and system configurations.

Autonomous Microrobotic Manipulation Using Visual Servo Control

“…As mentioned previously, the current implementation of the exit/separation strategy does not attempt to keep the manipuland error within a select tolerance (i.e., this set of control gains may reduce error if allowed to execute longer). Future work will investigate utilizing more robust control methodologies such as that of [16] to improve positioning capabilities. From Figure 8, the proposed method manipulated the 50-µm sphere to within 6.7 pixels of the desired target position parking the robot in 39.1 s. For this trial, algorithm stayed in exit mode of approximately 32.4 s as the robot experienced difficulty separating itself from the manipuland (this appeared be more of an adhesion phenomenon as opposed to a fluid interaction).…”

“…As mentioned previously, the current implementation of the exit/separation strategy does not attempt to keep the manipuland error within a select tolerance (i.e., this set of control gains may reduce error if allowed to execute longer). Future work will investigate utilizing more robust control methodologies such as that of [16] to improve positioning capabilities.…”

“…Such uncalibrated adaptive methods have been successfully implemented in macro-scale manipulators and mobile robots for a variety of applications with more complex nonlinear system models and higher degrees of freedoms (DOF) [13][14][15]. Our group has previously demonstrated an adaptive microrobot control scheme in two- [16] and three- [17] dimensions that uses recursive least squares (RLS) estimation to adaptively derive the relationship of the robot velocity to the control signal.…”

Closed-Loop Control of a Magnetic Particle at the Air–Liquid Interface

“…The fluid/fluid interface is also of interest for microrobotics: a magnetically actuated microrobot of typical size of 200 µm has been controlled in 2D at the interface between oil and sodium bicarbonate solution. However it demonstrates a low velocity of 23 µm/s [45].…”

“…The object is in equilibrium on the interface under the action of the surface tension and its weight, and it moves on the surface with minimum friction. A proof-of-concept was introduced in [46], where initial open loop experimental results were discussed and closed loop control has been performed in [45] but only low velocities have been achieved (less than 23 µm/s). In this present work, closed loop control is proposed based on a model of the system.…”