A robot is a system integrated with many elements such as actuators, sensors, computers, and mechanical components. Currently, progress in the field of artificial intelligence induced by tremendous improvements in computer processing capabilities has enabled robots to behave in a more sophisticated manner, which is drawing considerable attention. On the other hand, the mechanism that directly produces robot movements and mechanical work sometimes brings out some competencies that cannot be provided solely by computer control that relies on sensor feedback.

This special issue on “Integrated Knowledge on Innovative Robot Mechanisms” aims to introduce a knowledge system for robot mechanisms that bring forth useful and innovative functions and values.

The editors hope that the studies discussed in this special issue will help in the realization and further improvement of the mechanical functions of robots in the real world.

Microsurgery, often performed for anastomosis of small vessels and nerves, requires micro-manipulations of small tissues and thus requires highly specialized surgical skills. Robotic technology has great potential to assist with microsurgical treatments because of the high accuracy provided by robots; however, implementation remains challenging because the technical requirements of robotic surgery are far different from those in industry. One of the greatest challenges is that two surgical tools (e.g., tweezers) must be precisely and deftly moved around the surgical area in seven degrees of freedom (DOF) using one DOF to grasp each tool, and these tools are used in close proximity to each other. Additionally, high accuracy and rigidity at the tool tip are imperative for successful performance of the microsurgical procedure. In this study, we propose a new rotational two-DOF parallel mechanism that has the inherent advantages of a parallel mechanism, namely accuracy and rigidity, within a newly proposed spherical and non-spherical combined parallel structure to prevent collision of the two mechanisms in a dual-arm setup for microsurgery. The prototype was evaluated by performing a series of mechanical tests, and microsurgical suturing was performed by a microsurgical robotic system. The series of evaluations demonstrated the feasibility of the proposed mechanism.

In a previous study, we developed a seven-axis multi-joint gripper (MJG) with a mechanism for varying the joint stiffness and showed that it was capable of dexterous grasping. In this research, we expand this design by introducing a hand with several multi-jointed fingers. The mechanism of grasping with this hand involves the use of serially connected differential gear systems (DGSs). The DGSs are controlled by only two actuators: one for driving the joints simultaneously and the other for adjusting the stiffness of all of the joints. The hand is shown to successfully grasp and envelope objects of some shapes without sensory feedback and handle objects by pinching them with the finger tips and subsequently transitioning to an envelope grasp. The mechanism that significantly contributes to this result is the tip roller attached to the fingertip. It is incorporated into the joint drive mechanism using a DGS. These functionalities are considerably advantageous in scenarios where information about the objects to be grasped, such as the shape and precise position, cannot be obtained.

There have been numerous studies on the physical human-robot cooperative task system with impedance/admittance control in robot motion control. However, the problem of stability persists, wherein the control system becomes unstable when the robot comes into contact with a highly stiff environment. A variable impedance control strategy was proposed to circumvent this stability problem. However, a number of studies on variable impedance control are based on the variation of a parameter in the robot motion control software, and a mechanical variable impedance control has not been proposed. The purpose of this research is to propose a mechanical variable impedance control strategy using a mechanical device based on the lever principle. The proposed mechanism can adjust the magnitude of the input force to the force sensor by changing the position of application of the operating force on the beam. Adjusting the magnitude of the input force to the force sensor is equivalent to varying the impedance parameters of the robot; therefore, it is feasible to achieve mechanical variable impedance control using the proposed mechanism. In this study, the gain adjustment characteristics of the proposed mechanism were evaluated. The experimental results demonstrated that the operator can vary the impedance parameters of the robot by mechanically adjusting the input force to the force sensor and operating the robot using the proposed mechanism.

This paper discusses the positioning control of an elastic tendon-driven robot arm under gravity. The robot is driven by rubber string tendons and winding drums attached on the outside frames. Low-cost rubber strings that are available commercially are used as tendons. The goal is to utilize the nonlinear nature of the rubber materials to control a low-cost and soft robot arm. Theoretically, a mathematical model with accurate parameters and accurate measurement of the payload weight is necessary for rigorous gravity compensation. However, the necessity for the information of the robot parameters is hindering easy adaptability, versatility, and cost-efficiency. This paper presents an iterative estimation and compensation method for unknown payloads based on the steady-state position error and the nominal stiffness coefficient. Owing to the nonlinearity of the actual rubber strings, the position error remains after a single operation of the gravity compensation. However, experiments indicate that the error reduces by a simple iteration of the same compensation operation. Considering the nonlinearity in rubber strings, the mechanism of the error reduction is analyzed theoretically. Although the iterative process is time consuming, the method requires less prior information. In addition, it is cost effective because a sophisticated force sensor is not required. As the mechanism of error reduction applies to typical rubber string materials, it is useful for significant cost-reduction and reconfigurable robotics.

Robotic rehabilitation systems for upper limbs have been developed as two system types: active or passive. Active-type systems use actuators to provide users with varying degrees of force; in contrast, the force available from passive-type systems is limited, although these systems are safer to use. In this paper, a passive-type force display with redundant brakes is proposed to extend the displayable force region of the system. The kinematics and statics are derived, and the reaction force generated by brake torques is clarified. The displayable force region is analyzed in the simulation, and then the experiments are examined to verify the proposed analytical model.

This paper deals with an above-knee prosthesis (AKP) that allows stair ascending/descending with no external energy source. It controls the passive resistance and interlocking strength of the knee and ankle joints with a flow control valve (FCV) equipped with a hydraulic system. The FCV is also mechanically controlled by an automatic flow controller (AFC). Our previous study certified that the experimental AKP allows step-over-step gait in stair ascending and a slight knee flexion at the initial stage of the stance phase in level ground walking, as observed from non-amputees’ walking. However, the experiments showed that the AKP does not allow smooth flexing of the knee in the stance phase during stairs descending because of the improper timing of the AFC opening. This paper shows the total walking performance of the AKP equipped with a refined AFC.

In this study, we aimed to develop a mobile robot that can move forward, turn, and move backward using one actuator. We previously proposed 1-DOF swing motion drive mechanisms for a mobile robot that uses linear actuators. This paper proposes a 1-DOF swing motion robot with a rotary actuator for realizing simple design and cost reduction. First, this paper describes a wheel posture switching mechanism. Next, we examine the dynamics modeling of a mobile robot and the wheel posture switching mechanism. Finally, the results are investigated through dynamic simulations to determine the forward-movement characteristics of the proposed mechanism.

This paper presents kinematic and static analyses of an active-caster robotic drive with a single-layer ball transmission (ACROBAT-S). On the basis of the analyses, a single-wheel prototype is designed, and fundamental experiments using the prototype are conducted. The proposed ACROBAT-S includes a ball transmission that transmits power to a wheel axis and steering axis of an active-caster wheel in an appropriate ratio to produce so-called “caster motion.” The power distribution is realized mechanically rather than by complicated computer control algorithms. Therefore, the angle sensor for detecting the wheel orientation, and the control calculations for coordinated control of the wheel and steering motors of a conventional system are eliminated. Thus, the proposed mechanical design, which transfers a part of the control function to the mechanism, contributes to simplifying the overall control system. The results of the analyses and experiments with a prototype confirm that the proposed active-caster mechanism, ACROBAT-S, can realize the expected omnidirectional motion with simple motor control, such as Point-To-Point control.

For improving the classification accuracy of the classifier, a novel classification methodology based on artificial bee colony algorithm is proposed for optimal feature and SVM parameters selection. In order to balance the ability of exploration and exploitation of traditional ABC algorithm, improvements are introduced for the generation of initial solution set and onlooker bee stage. The proposed algorithm is applied to four datasets with different attribute characteristics from UCI and efficiency of the algorithm is proved from the results.

In realistic situations such as human-robot interactions or contact tasks, robots must have the capacity to adapt accordingly to their environment, other processes and systems. Adaptive model based controllers, that requires accurate dynamic and geometric robot’s information, can be used. Accurate estimations of the inertial and geometric parameters of the robot and end-effector are essential for the controller to demonstrate a high performance. However, the identification of these parameters can be time-consuming and complex. Thus, in this paper, a framework based on an adaptive predictive control scheme and a fast dynamic and geometric identification process is proposed. This approach was demonstrated using a KUKA lightweight robot (LWR) in the performance of a force-controlled wall-painting task. In this study, the performances of a generalized predictive control (GPC), adaptive proportional derivative gravity compensation, and adaptive GPC (AGPC) were compared. The results revealed that predictive controllers are more suitable than adaptive PD controllers with gravitational compensation, owing to the use of well-identified geometric and inertial parameters.

The transformation method that was originally used to tailor the physical fields into desired spatial patterns by designing material parameters is used herein to obtain necessary local dynamic parameters when the state distribution of a network system is prescribed in space. This constitutes a typical inverse problem that controls the state distribution of a complex network by designing its local dynamic parameters. Thus, it is difficult to obtain a direct solution. This coordinate transformation provides a direct method. The feasibility of this method is demonstrated and verified by two examples (a communication field bender and a communication field cloak) in corresponding network systems.

Smart material-based actuators and sensors have been widely used in practice owing to their various advantages. However, in the working process of these actuators and sensors, their output responses always deduce non-smooth nonlinear constraints. The constraint resulting from the actuator is called the input constraint and the constraint caused by the sensor is called the output constraint. These input and output constraints may induce inaccuracies and oscillations, severely degrading system performance. Therefore, the input and output constraints brought about by actuators and sensors should be considered in control system design. In this paper, system analysis for a nonlinear system with input and output constraints will be considered. The effect from the input constraint to the internal signal in the control system will be discussed. Moreover, the influence of the output constraint on the whole system will be studied. Further, the sufficient conditions for maintaining the stability of the system are obtained. Then, by using the robust right coprime factorization approach, an operator-based internal model like control structure is proposed for mitigating the input and output constraints. Finally, the effectiveness of the proposed design scheme will be confirmed through numerical simulation.

To solve the problems of incomplete consideration and low precision in existing domain ontology semantic similarity computation, an improved synthetic weighted algorithm of ontology-based semantic similarity computation is proposed, mixing path coincidence degree, the shortest distance, and concept property methods. First, the depths of lowest common ancestor (LCA) and an ontology tree are added to the formula of path coincidence degree for distinguishing the influence of LCA depth on similarity when multiple inheritances occur. Second, the analysis of similarity algorithm based on the shortest distance cannot distinguish two situations with the same path distance. One is when the density of LCA is different. The other is a depth difference in the concept pair. So, the number of direct subnodes of the LCA and the depth difference are added to the formula of the shortest distance. Meanwhile, the switch of density factor is set to ensure similarity calculation results between [0,1]. Then, a synthetic weighted algorithm of semantic similarity computation is constructed using the weighting path coincidence degree, the shortest distance, and the concept property. Finally, this algorithm and the other three algorithms in the literature are used to calculate semantic similarity in tea ontology. The results show that this algorithm is closest to expert experience.

This paper considers the absolute stability for Lur’e systems with time-varying delay and sector-bounded nonlinear. In this paper, a new relaxed condition based on delay decomposition approach is proposed. By using this technique and employing some inequality, the new delay-dependent stability criteria for Lur’e systems are derived in the form of linear matrix inequalities (LMIs). A numerical example is presented to show less conservatism of proposed methods compared with the previous.

This paper proposes a new method for cruising-type autonomous underwater vehicles (AUVs) to track rough seafloors at low altitudes while also maintaining a high surge velocity. Low altitudes are required for visual observation of the seafloor. The operation of AUVs at low altitudes and high surge velocities permits rapid seafloor imaging over a wide area. This method works without high-grade sensors, such as inertial navigation systems (INS), Doppler velocity logs (DVL), or multi-beam sonars, and it can be implemented in lightweight AUVs. The seafloor position is estimated based on a reflection intensity map defined on a vertical plane, using measurements from scanning sonar and basic sensors of depth, attitude, and surge velocity. Then, based on the potential method, a reference pitch angle is generated that allows the AUV to follow the seafloor at a constant altitude. This method was implemented in the AUV HATTORI, and a series of sea experiments were carried out to evaluate its performance. HATTORI (Highly Agile Terrain Tracker for Ocean Research and Investigation) is a lightweight and low-cost testbed designed for rapid and efficient imaging of rugged seafloors, such as those containing coral reefs. The vehicle succeeded in following a rocky terrain at an altitude of approximately 2 m with a surge velocity of approximately 0.8 m/s. This paper also presents the results of sea trials conducted at Ishigaki Island in 2017, where the vehicle succeeded in surveying the irregular, coral-covered seafloor.

After the occurrence of a disaster, it is critical to perform rapid and accurate searching operations in the large disaster area. It is efficient to perform such operations using multiple mobile exploration robots. Accordingly, we focus on cooperative cruising in a disaster environment and propose the trajectory tracking control method for a semi-autonomous search robot. We apply a robot operating system (ROS) to execute the trajectory tracking control using two mobile exploration robots. In this paper, we describe the trajectory tracking control using gravity potential method and the results of a cooperative cruising experiment in an uneven terrain environment.

Stress urinary incontinence (SUI) is a typical quality of life disease in women. The strengthening of the pelvic floor muscle (PFM) is considered effective to prevent this. Specifically, PFM activity is affected by individual pelvic shape and posture. Therefore, it is necessary to analyze muscle activity by considering the individual differences. In this study, individual pelvic alignment was estimated from the feature values of natural gait via multiple regression analysis. In addition, individual pelvic feature points were derived from X-ray images and used to deform the standard model to obtain individual pelvic shapes. Results indicate that the residual averages of the estimated feature angles were less than 2° in most cases. Subsequently, measurements of the pelvis were obtained via MRI to evaluate the estimated pelvis shape. The results indicate that individual adaptation leads to muscle attachment positions, which are important in the muscle activity analysis, and closer to the true MRI value when compared to that of the standard pelvic model.

The risk of collapse and subsidence of abandoned lignite mines has been noted in the Tokai region of Japan. The cavity-filling process by local governments has been ongoing. There is no cavity map in the abandoned lignite mines, and it is necessary to understand and explore the underground space in order to estimate the amount of filling material needed. By request from Mitake-cho in Gifu Prefecture, we received the opportunity to explore the inside of an abandoned lignite mine using our robotic system. Prior to the exploration of the actual abandoned lignite mine, as a feasibility study, an experimental test field that simulated the elements of the abandoned lignite mine was prepared outdoors. Some experiments were performed and the robotic exploration system was evaluated in this study. This paper describes the lessons learned from the feasibility study.

This letter presents the design of an optimal sinusoidal tracking and disturbance rejection controller for a linear voice-coil motor. The optimal tracking and disturbance rejection system is used to characterize the nonlinear dynamic friction of the servo motor. The control scheme allows investigating the hysteresis characteristics of friction as a function of frequency. Experimental results indicate the effectiveness of the proposed identification procedure for the dynamic friction estimation.