Microrobot Research Articles

Experiments in robust path following control of a rolling and spinning robot on outdoor surfaces

This paper presents path following control experiments of a miniature spherical rolling and spinning robot mechanism on three different types of outdoor surfaces. The research is inspired from the efficient locomotory rolling patterns of various insects in unstructured environment. A nonlinear adaptive sliding mode (ASMC) feedback method maintains the robot stability and robustness in the presence of parameter uncertainties and external disturbances. The proposed path following control policy is developed, implemented and tested for the miniature spherical robot on three different types of irregular surfaces in outdoors. Path following accuracy, roll angle stability and wheel velocity response are three parameters measured to evaluate robot performance. ASMC controller capability is compared with an integral sliding mode (ISMC) controller. Experimental results show that proposed nonlinear robust control policy precisely tracks the different paths on these irregular surfaces in practical outdoor conditions.

Miniature soft robots — road to the clinic

Soft small robots offer the opportunity to non-invasively access human tissue to perform medical operations and deliver drugs; however, challenges in materials design, biocompatibility and function control remain to be overcome for soft robots to reach the clinic.

Development and Analysis of a Three-Dimensional Printed Miniature Walking Robot With Soft Joints and Links

Miniature robots have many applications ranging from military surveillance to search and rescue in disaster areas. Nevertheless, the fabrication of such robots has traditionally been labor-intensive and time-consuming. This paper proposes to directly leverage multimaterial 3D printing (MM3P) to fabricate centimeter-scale robots by utilizing soft materials to create not only soft joints to replace revolute joints but also soft links to replace rigid links. We demonstrate the capability of MM3P by creating a miniature, four-legged walking robot. Moreover, we leverage a three-spring rotational-prismatic-rotational (RPR) model to approximate the motion of soft joints or links, which is further utilized to numerically predict the motion of the leg mechanism with multiple soft joints and links. The accuracy of the proposed numerical method is validated with experimental results, and outperforms the results from using a psuedorigid-body (PRB) 1R model to approximate the motion of soft joints/links of the same mechanism. Meanwhile, a functional walking robot actuated by a single DC motor is demonstrated with a locomotion speed of 5.7 cm/s. We envision that the concept of employing both soft joints and links will inspire the design and realization of novel miniature mechanisms for a wide range of applications including robotics, deployable structures, or mechanical metamaterials. The proposed numerical method can also be readily applied to analyze other mechanisms with soft joints and links.

Swimming Microrobots: Soft, Reconfigurable, and Smart

AbstractUsing materials with properties similar to those of cells and microorganisms together with innovative fabrication methods, soft and smart microrobots can be developed, with increased adaptability and flexibility toward in vivo applications. These tiny robots are designed to carry out difficult tasks such as noninvasive microsurgery, diagnosis and therapy in complex environments, including viscous media and intricate channels. Moreover, the novel property of the soft materials to respond to stimuli has paved the way for the creation of reconfigurable and smart microrobots with both actuation and function (e.g., sensing, drug delivery) capabilities. This feature article aims to give an overview of the different soft and smart swimming microrobots (less than 1 mm in all dimensions), highlighting some aspects of new materials, their development and the challenges in their processing to obtain highly functional microrobots.

Design and Analysis of a Rotational Leg-type Miniature Robot with an Actuated Middle Joint and a Tail (RoMiRAMT-II)

In this paper, a rotational leg-type miniature robot with a bioinspired actuated middle joint and a tail is proposed for stable locomotion and improved climbing ability. The robot has four independently actuated rotational legs, giving it advantages of both wheel-type and leg-type locomotion. The design parameters of the rotational legs were determined by 3D simulation within the seven candidates that selected by a newly proposed metric. It also has unique characteristics inspired by biological structures: a middle joint and a tail. An actuated middle joint allows the frontal body to be lifted or lowered, which was inspired by a flexible body joint of animals, to climb higher obstacles. Effectiveness of the middle joint was analytically verified by the geometric analysis of the robot. Additionally, a multi-functional one Degree Of Freedom (1-DOF) tail was added; the tail prevented the body being easily flipped, while allowed the robot to climb higher obstacles. A bristle-inspired micro structure was attached to the tail to enhance straightness of locomotion. Body size of the robot was 158 mm × 80 mm × 85 mm and weighed 581 g including a 7.4 V Li-Polymer battery. The average velocity of the robot was 2.74 m·s−1 (17.67 body lengths per second) and the maximum height of an obstacle that the robot could climb was 106 mm (2.5 times of leg length), which all were verified by experiments.

Distributed camouflage for swarm robotics and smart materials

We present a distributed algorithm for a swarm of active particles to camouflage in an environment. Each particle is equipped with sensing, computation, and communication, allowing the system to take color and gradient information from the environment and self-organize into an appropriate pattern. Current artificial camouflage systems are either limited to static patterns, which are adapted for specific environments, or rely on back-projection, which depend on the viewer’s point of view. Inspired by the camouflage abilities of the cuttlefish, we propose a distributed estimation and pattern formation algorithm that allows to quickly adapt to different environments. We present convergence results both in simulation as well as on a swarm of miniature robots “Droplets” for a variety of patterns.

Magnetic hammer propels tiny medical bot

A tiny robot that jackhammers its way through the body sounds like the stuff of science fiction nightmares. But such a robot exists, and it could play an important role in the future of medicine.

Design, Analysis, and Characterization of a Two-Legged Miniature Robot With Piezoelectric-Driven Four-Bar Linkage

This paper presents the design and development of a new type of piezoelectric-driven robot, which consists of a piezoelectric unimorph actuator integrated as part of the structure of a four-bar linkage to generate locomotion. The unimorph actuator replaces the input link of the four-bar linkage, and motion is generated at the coupler link due to the actuator deflection. A dimensional synthesis approach is proposed for the design of four-bar linkage that amplifies the small displacement of the piezoelectric actuator at the coupler link. The robot consists of two such piezo-driven four-bar linkages, and its gait cycle is described. The robot's speed is derived through kinematic modeling and experimentally verified using a fabricated prototype. The robot prototype's performance in terms of its payload capability and nominal operating power is also characterized experimentally. These results will be important for developing a motion planning control strategy for a autonomous robot locomotion, which will be part of future work.

Tiny robots, 3D images, and a honeycomb maze

Tiny robots, 3D images, and a honeycomb maze

Tiny robots could help infants with rare diseases. Watch one in action

Tiny robots could help infants with rare diseases. Watch one in action

Design and Fabrication of ER Brake for Micro-robot

Design and Fabrication of ER Brake for Micro-robot

Universal Custom Complex Magnetic Spring Design Methodology

A design methodology is presented for creating custom complex magnetic springs through the design of force-displacement curves. This methodology results in a magnet configuration, which will produce a desired force-displacement relationship. Initially, the problem is formulated and solved as a system of linear equations. Then, given the limited likelihood of a single solution being feasibly manufactured, key parameters of the solution are extracted and varied to create a family of solutions. Finally, these solutions are refined using numerical optimization. Given the properties of magnets, this methodology can create any well-defined function of force versus displacement and is model-independent. To demonstrate this flexibility, a number of example magnetic springs are designed; one of which, designed for use in a jumping–gliding robot’s shape memory alloy actuated clutch, is manufactured and experimentally characterized. Due to the scaling of magnetic forces, the displacement region which these magnetic springs are most applicable is that of millimeters and below. However, this region is well situated for miniature robots and smart material actuators, where a tailored magnetic spring, designed to compliment a component, can enhance its performance while adding new functionality. The methodology is also expendable to variable interactions and multi-dimensional magnetic field design.

Development of In-pipe Inspection Robot

In recent years, robotics has become an important domain in the field of engineering. It plays a crucial role in various fields, one of them being inspection purpose. In-pipe inspection robots are necessary for the safe and smooth running of industries. Problems arising in the piping network may lead to loss of the transported medium and leakage of which often affect the environment. Hence, it must be continuously inspected which involves large amount of labour. Also, the working environment usually involves possible exposure to hazardous chemicals or gases, humid and low oxygen content air, zones inaccessible to human hands, etc. Robots can act in an inaccessible environment and also reduce human effort. Therefore, inspection robots are strongly demanded. The main objective of the present work is to design a miniature robot which can adapt to narrow surfaces. In-pipe inspection robot using DC Motor (conventional actuators) is developed for this purpose. Modelling of the robot is done in SolidWorks. Simulations were performed for horizontal and vertical configuration of pipe and results were plotted. A prototype is developed and experiments were carried out in horizontal pipe. A comparison of results for different parameters obtained from simulation study and experimental work was done.

Gecko-Inspired Dry Adhesive Based on Micro–Nanoscale Hierarchical Arrays for Application in Climbing Devices

The unusual ability of geckos to climb vertical walls underlies a unique combination of a hierarchical structural design and a stiffer material composition. While a dense array of microscopic hierarchical structures enables the gecko toe pads to adhere to various surfaces, a stiffer material (β-keratin) composition enables them to maintain reliable adhesion over innumerable cycles. This unique strategy has been seldom implemented in engineered dry adhesives because fabrication of high-aspect-ratio hierarchical structures using a stiffer polymer is challenging. Herein, we report the fabrication of high-aspect-ratio hierarchical arrays on flexible polycarbonate sheets (stiffness comparable to that of β-keratin) by a sacrificial-layer-mediated nanoimprinting technique. Dry-adhesive films comprising the hierarchical arrays showed a formidable shear adhesion of 11.91 ± 0.43 N/cm2. Cyclic adhesion tests also showed that the shear adhesion of the adhesive films reduced by only about 20% after 50 cycles and remained nearly constant until about 200 cycles. Most importantly, the high-aspect-ratio hierarchical arrays were integrated onto the feet of a miniature robot and the locomotion on a 30° inclined surface was demonstrated.

Microbots that use magnetism to capture cells

Microbots that use magnetism to capture cells

Piezoelectric kinematic pairs with several DOF in miniature high-resolution piezoelectric robots

This paper presents results on the development and investigation of new miniature robots with increased number of degrees of freedom, based on the application of piezoelectric kinematic pairs with multi-DOF. The schematics of technologically advanced multi-DOF active kinematic pairs are presented and the details of their control are explained. The structure control of multi-DOF active kinematic pairs is based on sectioning of electrodes of the piezoelectric actuators and allows selecting desirable types of oscillations and speeds of links. Three modifications of piezoelectric robots with 6 and 15 DOFs are provided, together with their resolutions and responses to step inputs. Modal and harmonic analyses were performed and displacements of contact points were obtained. Trajectory planning algorithms are developed based on the numerical results.

Marangoni Effect-Driven Motion of Miniature Robots and Generation of Electricity on Water.

The well-known Marangoni effect perfectly supports the dynamic mechanism of organic solvent-swollen gels on water. On this basis, we report a series of energy conversion processes of concentrated droplets of polyvinylidene fluoride/dimethyl formamide (PVDF/DMF) that can transfer chemical-free energy to kinetic energy to rapidly rotate itself on water. This droplet (22.2 mg) is capable to offer kinetic energy of 0.099 μJ to propel an artificial paper rocket of 31.8 mg to move over 560 cm on water at an initial velocity of 7.9 cm s-1. As the droplet increases to 35.0 mg, a paper goldfish of 10.6 mg can be driven to swim longer at a higher initial velocity of 20 cm s-1. The kinetic energy of the droplet can be further converted to electrical energy through an electromagnetic generator, in which as a 0.5 MΩ resistor is loaded, the peak output reaches 6.5 mV that corresponds to the power density of 0.293 μW kg-1. We believe that this report would open up a promising avenue to exploit energies for applications in miniature robotics.

Jump stabilization and landing control by wing-spreading of a locust-inspired jumper

Bio-inspired robotics is a promising design strategy for mobile robots. Jumping is an energy efficient locomotion gait for traversing difficult terrain. Inspired by the jumping and flying behavior of the desert locust, we have recently developed a miniature jumping robot that can jump over 3.5 m high. However, much like the non-adult locust, it rotates while in the air and lands uncontrollably. Inspired by the winged adult locust, we have added spreading wings and a tail to the jumper. After the robot leaps, at the apex of the trajectory, the wings unfold and it glides to the ground. The advantages of this maneuver are the stabilization of the robot when airborne, the reduction of velocity at landing, the control of the landing angle and the potential to change the robot’s orientation and control its flight trajectory. The new upgraded robot is capable of jumping to a still impressive height of 1.7 m eliminating airborne rotation and reducing landing velocity. Here, we analyze the dynamic and aerodynamic models of the robot, discuss the robot’s design, and validate its ability to perform a jump-glide in a stable trajectory, land safely and change its orientation while in the air.

Measurement of wing deflections in flexible aircraft using the sansec smart sensor

Morphing aircraft are those that have the ability to actively change their shape in flight. There are several benefits of such shape change. For instance, since the optimal shape of an aircraft varies from one mission to another, the morphing concept enables a single aircraft to perform multiple missions during a single flight by executing its shape change feature. The morphing concept also enables an aircraft to achieve performance benefits, such as reduced drag during cruise and increased lift during take-off. The morphing concept is currently being investigated for both largescale passenger sized aircraft [1], as well as small-scale robotic micro air vehicles [2].

A Miniature Flexible-Link Magnetic Swimming Robot With Two Vibration Modes: Design, Modeling and Characterization

In this letter, we report a miniature swimming robot that consists of a nonmagnetic V-shaped head, an I-shaped tail attached with a magnet and a flexible link for interconnection of the rigid head and tail. The use of a flexible link enables the robot to exhibit two different vibration modes by tuning the input frequencies of the applied oscillating magnetic field with uniform field strength. When the input frequency is below 15 Hz, the head and tail show similar and large vibration amplitudes, and the net centrifugal force mainly contributes to the forward propulsion of the robot in fluid. While with high input frequencies (i.e., larger than 30 Hz), the flexible link can filter away high-frequency signals to efficiently avoid the passive vibration of the nonmagnetic head. Simultaneously, the magnetic tail vibrates with relatively large amplitude and generates forward propulsion force for the robot. To understand the whole-body-vibration and tail-vibration behaviors, an analytical model has been developed. Moreover, swimming performances of this robot, i.e., the propulsion force and swimming velocity, are characterized on the substrate-water interface. Finally, we demonstrate two-dimensional manipulation of tiny objects by utilizing the two vibration modes of the robot.