We present SoRo-Track, a two-axis soft robotic actuator (SRA) for solar tracking and building-integrated photovoltaic applications. SRAs are gaining increasing popularity compared to traditional actuators, such as dc motors and hydraulic or pneumatic pistons, due to their inherent compliance, low morphological complexity, high power-to-weight ratio, resilience to external shocks and adverse environmental conditions, design flexibility, ease of fabrication, and low costs. We present the design, modelling and experimental characterisation of SoRo-Track. Finally, we demonstrate the suitability of SoRo-Track for solar tracking applications, which makes it a viable component for dynamic building facades.

Self-organization is a phenomenon found in biomolecular self-assembly by which proteins are spontaneously driven to assemble and attain various functionalities. This study reports on self-organized behavior in which distributed centimeter-sized modules stochastically aggregate and exhibit a translational wheeling motion. The system consists of two types of centimeter-sized water-floating modules: a triangular-shaped module that is equipped with a vibration motor and a permanent magnet (termed the active module), which can quasi-randomly rove around; and circular modules that are equipped with permanent magnets (termed passive modules). In its quasi-random movement in water, the active module picks up passive modules through magnetic attraction. The contacts between the modules induce a torque transfer from the active module to the passive modules. This results in rotational motion of the passive modules. As a consequence of the shape difference between the triangular module and the circular module, the passive modules rotate like wheels, being kept on the same edges as the active module. The motion of the active module is examined, as well as the characteristics and behavior of the self-organization process.

We apply nonsmooth multibody dynamics to describe the motion of a microrobot which is driven by the wireless resonant magnetic microactuator. We first analyze the robot using a simplified analytical model, which allows us to derive characteristic and nondimensional parameters that describe its dynamics. We then perform a numerical study to analyze the nonlinearities. We predict several nonintuitive phenomena, such as switching of the direction of the velocity with changing excitation frequency, and show that both erratic and controlled motions occur under specific conditions. Our numerical results are qualitatively consistent with experimental observations and indicate that previous speculations on the motion mechanism were incorrect. The modeling method is general and readily applies to other microrobots as well.

We apply the Lagrangian technique to compute and analyze the magnetization and the magnetic torque on soft-magnetic shape-dominant structures. The main advantages are the considerable reduction of the computation time, constant computation times across the saturation limits, and a closed-form description of the magnetization in both the linear and the saturation region. The analysis of the Lagrange multiplier allows, for the first time, the analytic prediction of the evolution of the magnetic torque as a function of the direction and magnitude of the applied field. In addition, it allows one to quantify the saturation state of a body, which is then used to predict the torque on assembled structures where the classic method fails. The results are verified by experiments and finite element analysis.

We present a dynamic model of the wireless resonant magnetic microactuator (WRMMA), which is a key component of the MagMite family of microrobots. We analyze the interbody force and integrate the nonsmooth and nonlinear equations of motion using a time-stepping integration scheme. We investigate the influence of system parameters, such as friction, the frequency of the applied force, the magnitude of the applied field, the effect of a clamping force, and the effect on velocity when phase shifting the clamping signal with respect to the magnetic signal. Our results are qualitatively consistent with experimental observations, and explain several nonintuitive phenomena. We show that the robots are highly sensitive to the phase of the clamping force, that the velocity can switch directions with changing frequency, and that both erratic and controlled motion occur under specific conditions.

For the localization of minimally invasive medical devices, such as capsule endoscopes in the human body, ultrasound combines good resolution, minimal adverse health effects, high speed, adequate frame rates, and low cost. In the case of capsule endoscopes, small onboard ultrasonic emitters with minimal power requirements have the potential to provide significantly enhanced localization. We demonstrate for the first time acoustic emission in the kHz range using a wireless emitter based on the actuation principle of the wireless resonant magnetic microactuator developed recently in our institute. Our experiments show good agreement with the theoretical model, and simulations show the potential for high resolution localization.

Self-assembly is a process in which individual components form an organized structure as a consequence of local interactions. When using magnetics to create interaction forces, the magnetic flux distribution of a self-assembling system changes as its assembly state varies. Since Hall effect sensors are a convenient and effective means to detect changes in the magnetic field, we explore their applicability to monitoring the morphology of such magnetically self-assembling systems. We find that optimal positions for the sensor can be found where the flux changes maximally. Our analysis is applied to two different systems by deriving the flux changes for all possible states, and theoretical flux changes are verified with experiments. In addition, we show that a small number of sensors is sufficient for robust state determination. In addition to state detection, experiments show the potential for angle measurement for compliant cylindrical magnet joints using a single Hall sensor.

Capitalizing on advances in CMOS and MEMS technologies, microrobots have the potential to dramatically change many aspects of medicine by navigating bodily fluids to perform targeted diagnosis and therapy. Onboard energy storage and actuation is very difficult at the microscale, but externally applied magnetic fields provide an unparalleled means of wireless power and control. Recent results have provided a model for accurate real-time control of soft-magnetic bodies with axially symmetric geometries. In this paper, we extend the model to consider the real-time control of assembled-MEMS devices that may have significantly more complex geometries. We validate the model through FEM and experiments. The model captures the characteristics of complex 3-D structures and allows us, for the first time, to consider full 6-DOF control of untethered devices, which can act asinvivomicrorobots or as end-effectors of micromanipulation systems.

There is a clear trend toward the miniaturization of medical devices for minimally invasive medical procedures, ranging from diagnosis and targeted drug delivery to complex surgical interventions. Current research focuses on increasing the functionality of commercially successful capsule endoscope technology by developing active locomotion and telemetry. The size of such a capsule must not be larger than what a person can swallow without difficulty. One approach to increase functionality while still working within this size constraint is to build a modular robotic system in which the modules are swallowed one at a time, and the final assembly is performed inside the gastrointestinal (GI) tract. This paper addresses a fundamental challenge that must be be met for the success of such swallowable modular robots-their self-assembly. We propose to use magnets in a specific configuration on the mating faces of the modules. Our results show that high success rates can be achieved and snake-type robots can be self-assembled with compliant magnetic joints allowing them to adapt to highly irregular paths, such as the small intestine.

This paper presents the design of a multi-axis micro force-torque sensor. The sensor is able to measure forces along two axes and a torque perpendicular to these forces. The load is measured by capacitive comb drives which provide a high sensitivity. The microfabrication process, the sensor readout electronics as well as the calibration procedure are presented. The sensor was used to measure the force and torque on a magnetically actuated microrobot. This microrobot is assembled from microfabricated nickel parts for directed drug delivery inside the human body. Precise knowledge load on the microrobot is required for accurate positioning and control of the robot. The three-axis micro sensor is used to simultaneously measure the forces and torques acting on the microrobot in a magnetic field and thus provides valuable data for magnetic control methods of microrobots.