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Recently, aerial manipulations are becoming more and more important for the practical applications of unmanned aerial vehicles (UAV) to choose, transport, and place objects in global space. In this paper, an aerial manipulation system consisting of a UAV, two onboard cameras, and a multi-fingered robotic hand with proximity sensors is developed. To achieve self-contained autonomous navigation to a targeted object, onboard tracking and depth cameras are used to detect the targeted object and to control the UAV to reach the target object, even in a Global Positioning System-denied environment. The robotic hand can perform proximity sensor-based grasping stably for an object that is within a position error tolerance (a circle with a radius of 50 mm) from the center of the hand. Therefore, to successfully grasp the object, a requirement for the position error of the hand (=UAV) during hovering after reaching the targeted object should be less than the tolerance. To meet this requirement, an object detection algorithm to support accurate target localization by combining information from both cameras was developed. In addition, camera mount orientation and UAV attitude sampling rate were determined by experiments, and it is confirmed that these implementations improved the UAV position error to within the grasping tolerance of the robot hand. Finally, the experiments on aerial manipulations using the developed system demonstrated the successful grasping of the targeted object.

Unmanned systems such as legged robots require fast-motion responses for operation in complex environments. These systems therefore require explosive actuators that can provide high peak speed or high peak torque at specific moments during dynamic motion. Although hydraulic actuators can provide a large force, they are relatively inefficient, large, and heavy. Industrial electric actuators are incapable of providing instant high power. In addition, the constant reduction ratio of the reducer makes it difficult to eliminate the tradeoff between high speed and high torque in a given system. This study proposes an explosive electric actuator and an associated control method for legged robots. First, a high-power-density variable transmission is designed to enable continuous adjustment of the output speed to torque ratio. A heat-dissipating structure based on a composite phase-change material (PCM) is used. An integral torque control method is used to achieve periodic and controllable explosive power output. Jumping experiments are conducted with typical legged robots to verify the effectiveness of the proposed actuator and control method. Single-legged, quadruped, and humanoid robots jumped to heights of 1.5, 0.8, and 0.5 m, respectively. These are the highest values reported to date for legged robots powered by electric actuators.

The moment a legged robot touches the ground, the tip of its toe can experience a significant impact force. It is preferable to keep the landing impact force small because it causes imbalance and damage to the frame, motors, gears, and other components of the robot legs. In this paper, we propose a control method to mitigate the landing impact force by preliminary motion based on the proximity information of the tiptoe before landing. A proximity sensor is mounted on the tiptoe to detect the ground before landing, and feedback control is applied according to the sensor output to reduce the impact force. In landing experiments using a one-legged robot equipped with a proximity sensor on a tiptoe, we evaluated the effects of changing the sensor offset distance and the feedback gains on impact force mitigation. The results show that the landing impact force was mitigated by reducing the relative velocity of the tiptoe and the ground using the proposed proximity feedback control.

Recently, the development of agile-legged robots that mimic the structures and functions of biological muscles and tendons of quadruped mammals has attracted significant attention. The driving force of muscles and the elastic force of muscles and tendons can help improve the performances of these robots. Thus far, most of these robots have been developed based on the muscle-tendon complex of the lower legs. However, some mammals have a larger muscle-tendon complex on the upper legs, which contributes significantly to agile movements. In this study, a legged robot that mimics the functions of the bi-articular muscle-tendon complex of the thigh was developed, and its effects on static and dynamic movements were verified through simulations and experiments. While maintaining a static posture, the transfer of torque between two joints in the thigh mechanism reduced the power consumption by the robot’s motors by half, used for balancing the gravity of the robot. For a dynamic vertical jump, the motion trajectory generation for the robot was performed using non-linear optimization to maximize the jump height. As a result, the jump height was significantly enhanced by the effect of the thigh mechanism, and the height was more than twice the leg length.

In this paper, a parallel quadrupedal robot was designed that is capable of versatile dynamic locomotion and perception-less terrain adaptation. Firstly, a quadrupedal robot with a symmetric legs and a powerful actuator was implemented for highly dynamic movement. Then, a fast and reliable method based on generalized least square was proposed for estimating the terrain parameters by fusing the body, leg, and contact information. On the basis of virtual model control (VMC) with the quadratic program (QP) method, the optimal foot force for terrain adaptation was achieved. Finally, the results obtained by simulation and indoor and outdoor experiments demonstrate that the robot can achieve a robust and versatile dynamic locomotion on uneven terrain, and the rejection of disturbances is reliable, which proves the effectiveness and robustness of this proposed method.

Underwater robots are becoming increasingly important in various fields. Fish robots are attracting attention as an alternative to the screw-type robots currently in use. We developed a compact robot with a high swimming performance by mimicking the anatomical structure of fish. In this paper, we focus on the red muscles, tendons, and vertebrae used for steady swimming of fish. A robot was fabricated by replacing the red muscle structure with shape memory alloy wires and rigid body links. In our previous work, undulation motions with various phase differences and backward quadratically increasing inter-vertebral bending angles were confirmed in the air, while the swimming performance in insulating fluid was poor. To improve the swimming performance, an improved robot was designed that mimics the muscle contractions of mackerel using a pulley mechanism, with the robot named UEC Mackerel. In swimming experiments using the improved robot, a maximum swimming speed of 25.8 mm/s (0.11 BL/s) was recorded, which is comparable to that of other soft-swimming robots. In addition, the cost of transport (COT), representing the energy consumption required for robot movement, was calculated, and a minimum COT of 0.08 was recorded, which is comparable to that of an actual fish.

Aiming at highly dynamic locomotion and impact mitigation, this paper proposes the design and implementation of a symmetric legged robot. Based on the analysis of the three-leg topology in terms of force sensitivity, force production, and impact mitigation, the symmetric leg was designed and equipped with a high torque density actuator, which was assembled by a custom motor and two-stage planetary. Under the kinematic and dynamic constraints of the robot system, a nonlinear optimization for high jumping and impact mitigation is proposed with consideration of the peak impact force at landing. Finally, experiments revealed that the robot achieved a jump height of 1.8 m with a robust landing, and the height was equal to approximately three times the leg length.

The jumping motion of legged robots is an effective way to overcome obstacles in the rugged microgravity planetary exploration environment. At the same time, a quadruped robot with a manipulator can achieve operational tasks during movement, which is more practical. However, the additional manipulator will restrict the jumping ability of the quadruped robot due to the increase in the weight of the system, and more active degrees of freedom will increase the control complexity. To improve the jumping height of a quadruped robot with a manipulator, a bio-inspired take-off maneuver based on the coordination of upper and lower limbs is proposed in this paper. The kinetic energy and potential energy of the system are increased by driving the manipulator-end (ME) to swing upward, and the torso driven by the legs will delay reaching the required peak speed due to the additional load caused by the accelerated ME. When the acceleration of ME is less than zero, it will pull the body upward, which reduces the peak power of the leg joints. Therefore, the jumping ability of the system is improved. To realize continuous and stable jumping, a control framework based on whole-body control was established, in which the quadruped robot with a manipulator was a simplified floating seven-link model, and the hierarchical optimization was used to solve the target joint torques. This method greatly simplifies the dynamic model and is convenient for calculation. Finally, the jumping simulations in different gravity environments and a 15° slope were performed. The jump heights have all been improved after adding the arm swing, which verified the superiority of the bio-inspired take-off maneuver proposed in this paper. Furthermore, the stability of the jumping control method was testified by the continuous and stable jumping.

Legged robots imitating animals have become versatile and applicable in more application scenarios recent years. Most of their functions rely on powerful athletic abilities, which require the robots to have remarkable actuator capacities and controllable dynamic performance. In most experimental demonstrations, continuous hopping at a desired height is a basic required motion for legged robots to verify their athletic ability. However, recent legged robots have limited ability in balance of high torque output and actuator transparency and appropriate structure size at the same time. Therefore, in our research, we developed a parallel robot leg using a brushless direct current motor combined with a harmonic driver, without extra force or torque sensor feedback, which uses virtual model control (VMC) to realize active compliance on the leg, and a whole-leg control system with dynamics modeling and parameter optimization for continuous vertical hopping at a desired height. In our experiments, the robot was able to maintain stability during vertical hopping while following a variable reference height in various ground situations.

Load capacity is an important index to reflect the practicability of legged robots. Existing research into quadruped robots has not analyzed their load performance in terms of their structural design and control method from a systematic point of view. This paper proposes a structural design method and crawling pattern generator for a planar quadruped robot that can realize high-payload locomotion. First, the functions required to evaluate the leg’s load capacity are established, and quantitative comparative analyses of the candidates are performed to select the leg structure with the best load capacity. We also propose a highly integrated design method for a driver module to improve the robot’s load capacity. Second, in order to realize stable load locomotion, a novel crawling pattern generator based on trunk swaying is proposed which can realize lateral center of mass (CoM) movement by adjusting the leg lengths on both sides to change the CoM projection in the trunk width direction. Finally, loaded crawling simulations and experiments performed with our self-developed quadruped robot show that stable crawling with load ratios exceeding 66% can be realized, thus verifying the effectiveness and superiority of the proposed method.

Due to their light weight, flexibility, and low energy consumption, ionic electroactive polymers have become a hotspot for bionic soft robotics and are ideal materials for the preparation of soft actuators. Because the traditional ionic electroactive polymers, such as ionic polymer-metal composites (IPMCs), contain water ions, a soft actuator does not work properly upon the evaporation of water ions. An ionic liquid polymer gel is a new type of ionic electroactive polymer that does not contain water ions, and ionic liquids are more thermally and electrochemically stable than water. These liquids, with a low melting point and a high ionic conductivity, can be used in ionic electroactive polymer soft actuators. An ionic liquid gel (ILG), a new type of soft actuator material, was obtained by mixing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hydroxyethyl methacrylate (HEMA), diethoxyacetophenone (DEAP) and ZrO2 and then polymerizing this mixture into a gel state under ultraviolet (UV) light irradiation. An ILG soft actuator was designed, the material preparation principle was expounded, and the design method of the soft robot mechanism was discussed. Based on nonlinear finite element theory, the deformation mechanism of the ILG actuator was deeply analyzed and the deformation of the soft robot when grabbing an object was also analyzed. A soft robot was designed with the soft actuator as the basic module. The experimental results show that the ILG soft robot has good driving performance, and the soft robot can grab a 105 mg object at an input voltage of 3.5 V.

To design a soft robotic fish with high performance by a biomimetic method, we are developing a soft robotic fish using piezoelectric fiber composite (PFC) as a flexible actuator. Compared with the conventional rigid robotic fish, the design and control of a soft robotic fish are difficult due to large deformation of flexible structure and complicated coupling dynamics with fluid. That is why the design and control method of soft robotic fish have not been established and they motivate us to make a further study by considering the interaction between flexible structure and surrounding fluid. In this paper, acoustic fluid-structural coupling analysis is applied to consider the fluid effect and predict the dynamic responses of soft robotic fish in the fluid. Basic governing equations of soft robotic fish in the fluid are firstly described. The numerical coupling analysis is then carried out based on different structural parameters of soft robotic fish. Through the numerical analysis, a new soft robotic fish is finally designed, and experimental evaluation is performed. It is confirmed that the larger swimming velocity and better fish-like swimming performance are obtained from the new soft robotic fish. The new soft robotic fish is developed successfully for high performance.

In grasping of a robot hand, a contact timing of each finger has a influence on grasp success. In order to eliminate the gap and grasp an object quickly, proximity sensing from the robot surface is effective way. The sensor detects the object posture and distance in a several tens of millimeters from the robot surface. It enables that the robot adjusts postures and distance between the object and fingertips along the object surface. In this paper, we demonstrate a quick grasp with contacting each finger simultaneously by proximity sensors on fingertips. In order to realize the grasp by optical proximity sensors, we introduce our reflectance estimation of the object surface and calibration of the sensor output. This approach uses only the proximity sensor output and a relative moving distance of the fingertip. It is unnecessary to add extra equipment or sensor for estimation and calibration. It is possible to achieve the grasp regardless of the reflectance of the object surface. In the experiment, we confirmed that the approach can be applied to surface with different reflection characteristics (iron plate, aluminum plate, paper: cylinder and plane ), and the hand can grasp a object with various reflectance surfaces (31.9∼76.1%) quickly with contacting each fingertip within 0.056s.

In this paper, we develop a robot with the ability to secure human safety in humanrobot collisions arising in our living and working environments. The humansymbiotic service robot using compliant hybrid joints realizes human safety, absorbs impact force, and fulfills task. In unexpected or expected collisions with human, the arising impulse force is attenuated effectively by the proposed physical model. Owing to the displacement of the links, several recovery controls have been developed for the endeffector to maintain its desired task position after the collision. The force attenuation property has been verified through collision simulations and experiments in that the capability of the proposed passive arm in overcoming the limitations of active compliance control has been demonstrated.

In this paper, we develop a robot with the ability to secure human safety in human-robot collisions arising in our living and working environments. The human-symbiotic service robot using compliant hybrid joints realizes human safety, absorbs impact force, and fulfills task. In unexpected or expected collisions with human, the arising impulse force is attenuated effectively by the proposed physical model. Owing to the displacement of the links, several recovery controls have been developed for the end-effector to maintain its desired task position after the collision. The force attenuation property has been verified through collision simulations and experiments in that the capability of the proposed passive arm in overcoming the limitations of active compliance control has been demonstrated.