A multifunctional robotic system toward moveable sensing and energy harvesting

The operations of the triboelectric nanogenerator (TENG) highly rely on the availability of the mechanical motion source depending on the location, time, weather, etc. Thus, it is highly demanded to achieve moveable mechanical sensing and energy harvesting, but it is also challenging considering the system complexity, size, and weight. To this end, an electrostatic robotic system capable of locomotion, energy harvesting, and vibration sensing is proposed in this paper. The main body of the robot is an integration of an electrostatic actuator and a TENG, both of which share the same structure and materials and utilize the mechanical and electrical characteristics of electrostatic effects, respectively. The prototype is lightweight (2.46 g) and compact (3.7 cm in height and 9.1 cm in length), consisting of two conductive films as the main body in a zipper-like form and two flat conductive films as feet. Here we demonstrate the multifunctionality of this prototype by driving the robot crawling on the ground at a speed of 2.2 mm/s at maximum with a mini camera for monitoring, anchoring by electrostatic adhesive feet at the aim location where vibration is strong, sensing the vibration frequency accurately while having an average relative error of 8.7% in measuring the amplitude, and harvesting the energy by TENG. Such a multifunctional robotic system may enable broad potential applications in structural health monitoring, environmental surveillance, rescue, risky intervention, etc.

Biologically inspired electrostatic artificial muscles for insect-sized robots

Millimeter-sized electrostatic film actuators, inspired by the efficient spatial arrangement of insect muscles, achieve a muscle-like power density (61 W kg−1 ) and enable robotic applications in which agility is needed in confined spaces. Like biological muscles, these actuators incorporate a hierarchical structure, in this case, building from electrodes to arrays to laminates, and are composed primarily of flexible materials. So comprised, these actuators can be designed for a wide range of manipulation and locomotion tasks, similar to natural muscle, while being robust and compact. A typical actuator can achieve 85 mN of force with a 15 mm stroke, with a size of 28 × 5.7 × 0.330 mm3 and a mass of 92 mg. Two millimeter-sized robots, an ultra-thin earthworm-inspired robot, and an intestinal-muscle-inspired endoscopic tool for tissue resection, demonstrate the utility of these actuators. The earthworm robot undertakes inspection tasks: the navigation of a 5 mm channel and a 19 mm square tube while carrying an on-board camera. The surgical tool, which conforms to the surface of the distal end of an endoscope, similar to the thin, smooth muscle that covers the intestine, completes tissue cutting and penetrating tasks. Beyond these devices, we anticipate widespread use of these actuators in soft robots, medical robots, wearable robots, and miniature autonomous systems.

A biologically inspired, flapping wing, hybrid aerial-aquatic microrobot

From millimeter-scale insects to meter-scale vertebrates, several animal species exhibit multimodal locomotive capabilities in aerial and aquatic environments. To develop robots capable of hybrid aerial and aquatic locomotion, we require versatile propulsive strategies that reconcile the different physical constraints of airborne and aquatic environments. Furthermore, transitioning between aerial and aquatic environments poses substantial challenges at the scale of microrobots, where interfacial surface tension can be substantial relative to the weight and forces produced by the animal/robot. We report the design and operation of an insect-scale robot capable of flying, swimming, and transitioning between air and water. This 175-milligram robot uses a multimodal flapping strategy to efficiently locomote in both fluids. Once the robot swims to the water surface, lightweight electrolytic plates produce oxyhydrogen from the surrounding water that is collected by a buoyancy chamber. Increased buoyancy force from this electrochemical reaction gradually pushes the wings out of the water while the robot maintains upright stability by exploiting surface tension. A sparker ignites the oxyhydrogen, and the robot impulsively takes off from the water surface. This work analyzes the dynamics of flapping locomotion in an aquatic environment, identifies the challenges and benefits of surface tension effects on microrobots, and further develops a suite of new mesoscale devices that culminate in a hybrid, aerial-aquatic microrobot.

Ultra-thin, Flexible Climbing Robots Integrating Both Electrostatic Actuation and Adhesion

Planar and flexible climbing robots suffer from buckling while climbing on a vertical surface. This paper analyzes two different modes: one-end free buckling and two-ends fixed buckling. As an example for buckling analyses, the paper focuses on an electrostatic climbing robot that features a thin body. As the body of the robot has only 2.5 mm of thickness, it is more prone to buckling than any other flexible robots, making it the best example for the buckling problem. Based on the analyses, the paper proposes a buckling-free control strategy for the electrostatic robots. The proposed strategy guarantees the force balance between adhesive force and weight force, as well as the elastic stability of the robot. To implement the strategy, the paper investigates the available region of the proper forces and optimal parameters on the prototype robot. A prototype of a climbing robot was developed to verify the analyses and solutions, weighing merely 29 g (excluding battery and control circuits). It successfully climbed up a vertical wall without buckling, carrying the payload of 0.4 N.

Using the novel electrostatic actuators and electrodense films (instead of conventional motors and magnets) for actuation and latching respectively, we build ultra-thin (2.5 mm high) and flexible (no rigid component) climbing robots (distinguished them from the conventional rigid clumsy climbing robots), which can be applied to the inspection in a narrow gap or confined space.

A hybrid terrestrial-aquatic microrobot

Several animal species demonstrate remarkable locomotive capabilities on land, on water, and under water. A hybrid terrestrial-aquatic robot with similar capabilities requires multimodal locomotive strategies that reconcile the constraints imposed by the different environments. Here we report the development of a 1.6 g quadrupedal microrobot that can walk on land, swim on water, and transition between the two. This robot utilizes a combination of surface tension and buoyancy to support its weight and generates differential drag using passive flaps to swim forward and turn. Electrowetting is used to break the water surface and transition into water by reducing the contact angle, and subsequently inducing spontaneous wetting. Finally, several design modifications help the robot overcome surface tension and climb a modest incline to transition back onto land. Our results show that microrobots can demonstrate unique locomotive capabilities by leveraging their small size, mesoscale fabrication methods, and surface effects.

Flexible Manipulator Actuated by Electroactive Polymers

Multiple-segment flexible and soft robotic arms composed by ionic polymer–metal composite (IPMC) flexible actuators, although promising in complex tasks such as crossing body cavities to grasp objects, exhibit compliance but suffer from the difficulty of path planning due to their redundant degrees of freedom. We propose a learning from demonstration method to plan the motion paths of IPMC based manipulators by statistics machine-learning algorithms. To encode demonstrated trajectories and estimate suitable paths for the manipulators to reproduce the task, models are built based on Gaussian Mixture Model and Gaussian Mixture Regression, respectively. The forward and inverse kinematic models of IPMC based soft robotic arm are derived for the motion control. A flexible and soft robotic manipulator is implemented with six IPMC segments, and it verifies the learned paths by successfully completing a representative task of navigating through a narrow keyhole.

Delicate Manipulations with Compliant Mechanism and Electrostatic Adhesion

Traditional rigid robotic hand manipulator has been used in many fields nowadays due to its advantages of large gripping force and stable performance. However, this kind of rigid manipulator is not suitable for gripping fragile objects since it is motorized, and its force control can be a problem. It is also not applicable to grip objects with different shapes since the manipulator is not compliant. In this study, a novel manipulator with gripping capability is designed and fabricated. The manipulator combines electrostatic adhesion actuation with soft manipulators. The manipulator has high flexibility and can be compliant with different shapes due to the materials' property, exhibiting promising potential in delicate manipulations in the industry and biomedical fields.

Acoustic Diagnosis of Railways System by Microphone Arrays

- Built a model for localization and tracking of multiple sound sources
- Designed and fabricated the mechanical structures and the circuit of microphone arrays for sound-source localization and tracking

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