Small Robot Research Articles

Ultra-stable and tough bioinspired crack-based tactile sensor for small legged robots

For legged robots, collecting tactile information is essential for stable posture and efficient gait. However, mounting sensors on small robots weighing less than 1 kg remain challenges in terms of the sensor’s durability, flexibility, sensitivity, and size. Crack-based sensors featuring ultra-sensitivity, small-size, and flexibility could be a promising candidate, but performance degradation due to crack growing by repeated use is a stumbling block. This paper presents an ultra-stable and tough bio-inspired crack-based sensor by controlling the crack depth using silver nanowire (Ag NW) mesh as a crack stop layer. The Ag NW mesh inspired by skin collagen structure effectively mitigated crack propagation. The sensor was very thin, lightweight, sensitive, and ultra-durable that maintains its sensitivity during 200,000 cycles of 0.5% strain. We demonstrate sensor’s feasibility by implementing the tactile sensation to bio-inspired robots, and propose statistical and deep learning-based analysis methods which successfully distinguished terrain type.

Energy in Robotics: An Interdisciplinary Challenge

Energy in Robotics: An Interdisciplinary Challenge

An Autonomous Clutter Inspection Approach for Radiological Survey Using Mobile Robot

In the event of a radiological emergency, scattered clutters around the accident sites should be thoroughly inspected as they are potentially contaminated and require proper safety handling. The goal of this work was to localise the position of the hotspot within the clutters and estimate their respective radiation intensity using a mobile robot. Given the information from a 2D occupancy map, we proposed a strategy to identify the position of clutters and formulate waypoints that simultaneously serve as sampling positions to acquire radiation measurement. Particle filter was adapted to fuse the measured data and provide the results in real-time. We also introduced clutter contamination analysis that takes into account the limitations of the detector to derive the worst-case scenario; thus, preventing misclassifications of hotspots with low radiation intensity as clean areas. The approach was implemented in ROS and a commercial mobile robot with a Geiger Muller detector. Finally, we evaluated the overall performance in simulation and real-world experiments. Note to Practitioners—This work was motivated by the goal of realising automation of clutter inspection using a mobile robot to complement the current achievement in robotics radiation mapping. Currently, we still rely on human workers to conduct a thorough radiation survey, including detailed inspections on all clutters, before clearing any radiological accident or incident site. The theoretical framework in this paper proposed a practical solution to localise and estimate the intensity of the hotspot within the clutter in real-time. We demonstrated the versatility and performance of our proposed approach using a small commercial robot and Geiger Muller tube (typically available in any radiation facilities). This method reduces radiation exposure to human workers and provides a cost-effective solution for preliminary screening in radiological emergency situations.

4D printed untethered milli-gripper fabricated using a biodegradable and biocompatible electro- and magneto-active hydrogel

Recently, four-dimensional (4D) printed hydrogel soft robots have attracted attention owing to their simple, repeatable, and accurate manufacturing. However, for application as medical robots, these 4D printed hydrogel soft robots should be biocompatible and biodegradable. Therefore, in this paper, a 4D printed untethered milli-gripper fabricated using a bio-three-dimensional (3D) printer and an ink composed of a biocompatible and biodegradable chitosan hydrogel and biocompatible citric acid-coated superparamagnetic iron oxide nanoparticles (SPIONs) is proposed. Since the untethered milli-gripper is printed by bio-3D printer, it can be fabricated quickly and precisely with high precision. As the untethered milli-gripper comprises an electroactive hydrogel, its bending angle and speed are precisely controlled by adjusting the electric field strength. Through this, gripping and releasing of cargo were possible. Additionally, because the citric acid-coated SPIONs have high magnetization values, the untethered milli-gripper demonstrates precise position control. Therefore, a cargo delivery is demonstrated in which the untethered milli-gripper grips a cargo, moves it to the desired position, and then release it under an applied electromagnetic field. Moreover, the untethered milli-gripper exhibits excellent cargo-handling ability and can grip and lift cargoes of various size, shapes, and numbers. Furthermore, it is biodegradable due to the presence of chitosan in it, and the citric acid-coated SPIONs remaining after biodegradation demonstrate biocompatibility. Accordingly, the proposed untethered milli-gripper can be used as a minimally invasive small soft robot in vivo for several purposes in the biomedical field.

Blind as a Bat: Audible Echolocation on Small Robots

For safe and efficient operation, mobile robots need to perceive their environment, and in particular, perform tasks such as obstacle detection, localization, and mapping. Although robots are often equipped with microphones and speakers, the audio modality is rarely used for these tasks. Compared to the localization of sound sources, for which many practical solutions exist, algorithms for active echolocation are less developed and often rely on hardware requirements that are out of reach for small robots. We propose an end-to-end pipeline for sound-based localization and mapping that is targeted at, but not limited to, robots equipped with only simple buzzers and low-end microphones. The method is model-based, runs in real time, and requires no prior calibration or training. We successfully test the algorithm on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e-puck</i> robot with its integrated audio hardware, and on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Crazyflie</i> drone, for which we design a reproducible audio extension deck. We achieve centimeter-level wall localization on both platforms when the robots are static during the measurement process. Even in the more challenging setting of a flying drone, we can successfully localize walls, which we demonstrate in a proof-of-concept multi-wall localization and mapping demo.

Adapting small jumping robots to compliant environments.

Jumping animals launch themselves from surfaces that vary widely in compliance from grasses and shrubs to tree branches. However, studies of robotic jumpers have been largely limited to those jumping from rigid substrates. In this paper, we leverage recent work describing how latches in jumping systems can mediate the transition from stored potential energy to kinetic energy. By including a description of the latch in our system model of both the jumper and compliant substrate, we can describe conditions in which a jumper can either lose energy to the substrate or recover energy from the substrate resulting in an improved jump performance. Using our mathematical model, we illustrate how the latch plays a role in the ability of a system to adapt its jump performance to a wide range of substrates that vary in their compliance. Our modelling results are validated using a 4 g jumper with a range of latch designs jumping from substrates with varying mass and compliance. Finally, we demonstrate the jumper recovering energy from a tree branch during take-off, extending these mechanistic findings to robots interacting with a more natural environment.

Underwater Formation System Design and Implement for Small Spherical Robots

Aiming at the difficulty of communication and positioning of the existing underwater robot system, this article combines the vision system with a closed leader–follower formation structure to realize the underwater formation of three underwater robots. On account of the long-standing tracking requirements during vision-based formation process, an antiloss and redetecting strategy is fused in the proposed detecting and tracking algorithm and the binocular vision system can achieve real-time positioning underwater and calculate the 3-D coordinate so as to complete the follower's follow-up to the leader. An artificial submarine detection experiment and an antiloss redetection experiment are applied to demonstrate the robustness of the algorithm. And the underwater formation experiment is implemented so that the effectiveness of the proposed vision-based formation strategy is proved, which also provides a new solution for expanded formation system and multilevel cooperation.

싱글포인트 라이다 기반 실내지도 생성시간 감소 기법

Indoor mapping technology is utilized as a digital twin-based technology in various fields that require information about indoor spaces, such as building and facility management services, smart factories, smart yards, etc. Sensors utilized for mapping include LiDAR. For certain services using constraint hardware such as small robots, it is appropriate to utilize single-point LiDAR, which is relatively cost-effective compared to high-performance LiDAR, but at the same time, the processing time is quite large to generate indoor maps using such sensors that identify only one point. Therefore, in this study, we propose a scheme to reduce the time for generating indoor maps based on single-point lidar. The proposed method consists of measurement, feature detection and partial map generation, partial map matching, and navigation to the next measurement point. By searching for points that can increase the measurement rate of unmeasured areas in the next measurement, the number of measurements is reduced, thereby reducing the total processing time. The proposed method is evaluated through experiments in a testbed environment by fabricating a mobile measurement device.

Design and experiments of a small resonant inchworm piezoelectric robot

Design and experiments of a small resonant inchworm piezoelectric robot

Automatic travelling of agricultural support robot for a fruit farm -Verification of effectiveness of RTK-GNSS and developed simulator for specification design

Labour shortages and fatal accidents in agricultural work have recently emerged as critical problems in Japan, necessitating productivity enhancement, workload reduction, and safety assurance. Therefore, in Japan and countries with similar agricultural environments, the use of small and inexpensive agricultural robots that can be used in mountain farms and orchards is desirable. In this study, a dynamic positioning test was performed in orchards in a mountainous region to verify the positioning accuracy and stability of the Global Navigation Satellite System (GNSS) and real time kinematic (RTK)-GNSS. In addition, a simulator for an agricultural robot that could consider the environmental information of orchards was developed, and driving tests were conducted using the GNSS data acquired in the simulation. The error of the GNSS module was set to be higher than that for the measured value, and robot travelling in the orchard was simulated. The results of GNSS positioning tests in an orchard near a mountainous area indicate that in the specific environmental conditions, the RTK-GNSS and stand-alone (SA)-GNSS can attain a positioning accuracy with an order of tens of centimetres and few metres, respectively. Moreover, the simulation results based on the GNSS positioning results indicate that a vehicle implementing RTK-GNSS and a simple obstacle detection sensor can travel autonomously in a farmyard without colliding with the tree rows. In contrast, a vehicle implementing SA-GNSS and a simple obstacle detection sensor cannot drive autonomously in an orchard and must realise self-positioning using a more accurate sensor. Therefore, the proposed approach of realising simulations of autonomous agricultural robots based on GNSS data from a real orchard can facilitate the evaluation of practical agricultural robots and confirming safety traveling root. The results demonstrate the possibility of development of small agricultural robot for orchards. We conducted the GNSS positioning test in an orchard at an altitude of approximately 830 m, and a similar performance can be expected under similar agricultural situations because the error of the GNSS module was set to be higher than the measured value in driving simulation test.

Fundamentals of burrowing in soft animals and robots.

Creating burrows through natural soils and sediments is a problem that evolution has solved numerous times, yet burrowing locomotion is challenging for biomimetic robots. As for every type of locomotion, forward thrust must overcome resistance forces. In burrowing, these forces will depend on the sediment mechanical properties that can vary with grain size and packing density, water saturation, organic matter and depth. The burrower typically cannot change these environmental properties, but can employ common strategies to move through a range of sediments. Here we propose four challenges for burrowers to solve. First, the burrower has to create space in a solid substrate, overcoming resistance by e.g., excavation, fracture, compression, or fluidization. Second, the burrower needs to locomote into the confined space. A compliant body helps fit into the possibly irregular space, but reaching the new space requires non-rigid kinematics such as longitudinal extension through peristalsis, unbending, or eversion. Third, to generate the required thrust to overcome resistance, the burrower needs to anchor within the burrow. Anchoring can be achieved through anisotropic friction or radial expansion, or both. Fourth, the burrower must sense and navigate to adapt the burrow shape to avoid or access different parts of the environment. Our hope is that by breaking the complexity of burrowing into these component challenges, engineers will be better able to learn from biology, since animal performance tends to exceed that of their robotic counterparts. Since body size strongly affects space creation, scaling may be a limiting factor for burrowing robotics, which are typically built at larger scales. Small robots are becoming increasingly feasible, and larger robots with non-biologically-inspired anteriors (or that traverse pre-existing tunnels) can benefit from a deeper understanding of the breadth of biological solutions in current literature and to be explored by continued research.

Lightweight underwater robot developed for archaeological surveys and excavations

This paper reports the development of a lightweight remotely operated vehicle that performs underwater excavation work for archaeological surveys. Discovering underwater artifacts is generally difficult because they are in high risk areas and are often covered with sediment. To discover them, divers and large remotely operated vehicles must conduct excavation work with a manipulator(s). Nevertheless, accomplishing such tasks is difficult for small and portable underwater robots without a manipulator(s). As described herein, we developed a lightweight underwater robot of 35 kg that can remove sediment from the seabed or lake bottom using its thrusters instead of a manipulator. Numerous redundant thrusters are equipped with the robot to compensate the reaction force of the thrusters for sediment removal. Eight thrusters are arranged not only for sediment removal but also for fine maneuvering. First, through preliminary experiments, we investigated the potential use of a water flow generated using a pair of small marine thrusters to remove surface sediment. Next, we described the design and development of a lightweight underwater robot with eight thrusters and high-definition cameras for archaeological surveys. Finally, we conducted field experiments to demonstrate the sediment removal performance and usefulness of the developed robot.

Intelligent Insect–Computer Hybrid Robot: Installing Innate Obstacle Negotiation and Onboard Human Detection onto Cyborg Insect

Developing small mobile robots for Urban Search and Rescue (USAR) is a major challenge due to constraints in size and power required to perform vital functions such as obstacle navigation, victim detection, and wireless communication. Drawing upon the idea that insects’ locomotion can be controlled, what if we further utilize the insects’ intrinsic ability to avoid obstacles? Herein, a cockroach hybrid robot (≈ 1.5 cm height, 5.7 cm length) that implements the abovementioned functions is developed. It is tested in an arena with randomly placed obstacles, and a motion capture system is used to track the insect's position among the untracked obstacles. A navigation algorithm that uses an inertial measurement unit (IMU) is developed to heuristically predict the insect's situation and stimulate the insect to escape nearby obstacles. The utilization of insect's intrinsic locomotor ability and low‐powered IMU reduces the onboard power load, allowing the addition of a human‐detecting function. An image classification model enables the use of an onboard low‐resolution infrared camera for human detection. Consequently, a single hybrid robot is established that includes locomotion control, autonomous navigation in obstructed areas, onboard human detection, and wireless communication, representing a significant step toward real USAR application.

Metamorphic aerial robot capable of mid-air shape morphing for rapid perching

Aerial robots can perch onto structures at heights to reduce energy use or to remain firmly in place when interacting with their surroundings. Like how birds have wings to fly and legs to perch, these bio-inspired aerial robots use independent perching modules. However, modular design not only increases the weight of the robot but also its size, reducing the areas that the robot can access. To mitigate these problems, we take inspiration from gliding and tree-dwelling mammals such as sugar gliders and sloths. We noted how gliding mammals morph their whole limb to transit between flight and perch, and how sloths optimized their physiology to encourage energy-efficient perching. These insights are applied to design a quadrotor robot that transitions between morphologies to fly and perch with a single-direction tendon drive. The robot’s bi-stable arm is rigid in flight but will conform to its target in 0.97 s when perching, holding its grasp with minimal energy use. We achieved a 30% overall mass reduction by integrating this capability into a single body. The robot perches by a controlled descent or a free-falling drop to avoid turbulent aerodynamic effects. Our proposed design solution can fulfill the need for small perching robots in cluttered environments.

Directionally Compliant Legs Enabling Crevasse Traversal in Small Ground‐Based Robots

Small ground‐based robots show promise for locomotion on complex surfaces. A critical application area for such robots is movement over complex terrain and within constricted space such as narrow gaps in rubble. To contend with this terrain complexity, robots typically require high degree‐of‐freedom (DOF) limbs. However, for small robot platforms, this approach of high DOF legs is impractical due to actuator limitations. This presents an opportunity to design robots whose morphology enables the outsourcing of computational tasks to the robot body through the use of compliant elements (morphological computation). Herein, a novel robot appendage is developed that can passively compress in a programmed direction in response to environmental constrictions. A robot equipped with these appendages can enter narrow spaces down to 72% of the robot's sprawled body width as well as low ceilings down to 68% its freestanding height. The robot is able to step onto and over small terrain features ( hip height) and navigate various natural terrain types with ease. The results show that these compressible appendages enable versatile robot locomotion for robot exploration in previously unmapped environments.

Trot Gait Stability Control of Small Quadruped Robot Based on MPC and ZMP Methods

The stability of a quadruped robot is mainly affected by the obstacles in the horizontal direction and the roughness in the vertical direction, which often leads to the robot unable to achieve the desired gait effect. In order to solve this problem, the Model Predictive Control (MPC) model and the Zero Moment Point (ZMP) method are combined, and applied to gait planning and the foot end landing control of a small quadruped robot. The tort gait of a small quadruped robot is the focus of research in this study, which simulated trajectory planning and gait stability. In addition, through comparative analysis with the corresponding experiments, the results show that the simulation results are similar to the experimental results, and the quadruped robot gait is stable. Meanwhile, it shows that the combination of the MPC model and ZMP method is feasible for gait stability control of a quadruped robot.

Research on Body Tube Vibration Response of Small Combat Robots Motion

As a hot topic in military research, small combat robots are always in a dynamic process when traveling, causing the body tube to vibrate which affects its firing accuracy. Different from the traditional two‐degree‐of‐freedom combat robot, this paper establishes a rigid‐flexible coupling dynamics model for the new three‐degree‐of‐freedom combat robot to study the response characteristics of its body tube during travel. To accurately reflect the driving conditions of the mobile robot, a road surface unevenness model was established using the sine wave superposition method. The firing accuracy of a small combat robot can be affected by the speed and road conditions, as shown in numerous studies. The effects of arm structure, arm mounting position, and firing angle on the vibration response of the body tube are analyzed in this paper. The results show that a reference for improving the design of small combat robots can be found in a correlation between the structure, mounting position, and firing angle of the robotic arm, and the body tube’s vibration response.

Distributed Optimal Control Framework for High-Speed Convoys: Theory and Hardware Results

Practical deployments of coordinated fleets of mobile robots in different environments have revealed the benefits of maintaining small distances between robots, especially as they move at higher speeds. However, this is counter-intuitive in that as speed increases, reducing the amount of space between robots also reduces the time available to the robots to respond to sudden motion variations in surrounding robots. However, in certain examples, the benefits in performance due to traveling at closer distances can outweigh the potential instability issues, for instance, autonomous trucks on highways that optimize energy by vehicle “drafting” or smaller robots in cluttered environments that need to maintain close, line of sight communication, etc. To achieve this kind of closely coordinated fleet behavior, this work introduces a model predictive optimal control framework that directly takes non-linear dynamics of the vehicles in the fleet into account while planning motions for each robot. The robots are able to follow each other closely at high speeds by proactively making predictions and reactively biasing their responses based on state information from the adjacent robots. This control framework is naturally decentralized and, as such, is able to apply to an arbitrary number of robots without any additional computational burden. We show that our approach is able to achieve lower inter-robot distances at higher speeds compared to existing controllers. We demonstrate the success of our approach through simulated and hardware results on mobile ground robots.

A Small Inspection Robot Walking on Structural Surfaces

A Small Inspection Robot Walking on Structural Surfaces

Development of a Small Jumping Robot Inspired by the Hip Joint Structure of Issus coleoptratus nymphs

Development of a Small Jumping Robot Inspired by the Hip Joint Structure of Issus coleoptratus nymphs