The significance of physical human-robot interaction (pHRI) with collaborative robots in the industry is growing steadily. Within this domain, an admittance controller is crucial for enabling robots to follow or assist human intentions. However, a persistent challenge with admittance controllers is ensuring their passivity. Various strategies have been developed to address this issue by adjusting the control signals derived from the admittance model. While these strategies achieve passivity, they often inadvertently impact collaborative performance, preventing the system from accurately aligning with the intended dynamics. Accordingly, this paper introduces an adaptive hierarchical control approach for redundant robots to handle this problem. This approach diverts non-passive power into the null space without diminishing the robot’s responsiveness to human input. Implementing this null-space controller involves the dynamic adjustment of compliance control error, ensuring joint limit avoidance while facilitating integration with energy tanks for enhanced reliability. Moreover, the method enables the calculation of adaptive error gain in a closed form, simplifying its real-time application. Experimental validation with a 7-DOF manipulator showed a reduction of non-passive energy from 1.61 J to 0.12 J without compromising task performance.

As a collaboration between humans and robots becomes critical, stiffness control of the robot is essential for stability and efficiency of work. Therefore, research on the variable stiffness mechanism is being actively conducted in service robots, soft robots, and exoskeletons. The main types of variable stiffness mechanisms are jamming effect (particle jamming and layer jamming), shape memory polymer (SMP), and low melting point alloy (LMPA). The case of the jamming effect uses negative pneumatic pressure to change the stiffness. Because of that, it is possible to change the stiffness quickly, and it is easy to manufacture. However, both SMP and LMPA use thermal energy to increase the material’s stiffness. There is a risk of damage to humans or robots, and it takes much time to change the stiffness. Therefore, this study introduces a variable stiffness mechanism that combines particle jamming and core-frame. In addition, optimization studies are being conducted to use the jamming effect in industries. However, due to the randomness of particle jamming, the existing studies assumed that the variable stiffness mechanism was a simple beam or modeled it using hook’s law, so the accuracy was low. Therefore, in this study, five design variables are selected for particle and core-frame, the main elements constituting the variable stiffness mechanism. In addition, design variables are optimized through various FEM simulations. Furthermore, the simulation is proved by establishing a theoretical model for variable stiffness structure when the jamming effect occurs. Finally, the optimization of five design variables is proved through experiments.

Super-coiled polymer (SCP) artificial muscles have many interesting properties that show potentials for making high performance bionic devices. To realize human-like robotic devices from this type of actuator, it is important for the SCP driven mechanisms to achieve human-like performance, such as compliant behaviors through antagonistic mechanisms. This paper presents the simultaneous position-stiffness control of an antagonistic joint driven by hybrid twisted-coiled polymer actuation bundles made from Spandex and nylon fibers, which is a common human compliant behavior. Based on a linear model of the system, which is identified and verified experimentally, a controller based on model predictive control (MPC) is designed. The MPC performance is enhanced by the incorporation of time delay estimation to estimate model variations and external disturbances. The controlled system is verified through simulations and experiments. The results show the controller's ability to control the joint angle with the highest position error of 0.6 degrees while changing joint stiffness, verified with step command and sinusoidal reference with composite frequencies of 0.01Hz to 0.1Hz.

This paper introduces a force-controllable quadruped robot system consists of twelve Actuator Modules embedded a novel Capacitive-type Joint Torque Sensor (CJTS) which is accurate (0.05 Nm), robust to impact, and easy to manufacture at low cost. The Actuator Module with CJTS shows accurate joint torque controllability in range of ±70 Nm (90 % settling time 0.04 s). The leg made by the three Actuator Modules is capable of generating forces in the z-axis up to 350 N and shows force control performances with zero-force control and lifting weights in three-dimensional space. To reduce the reflected limb inertia, all the Actuator Modules are located on the body frame and light-weight limbs made of the carbon pipe (3.6 % of total body weight). The introduced robot performed the motion on various terrains with walking/trot gaits.

The Elastic Inflatable Actuators (EIAs) has several advantages such as the inherent compliance due to the body comprised of a soft materials such as silicone. Among them, the soft fiber reinforced actuator is based on the principle that the expansion of enclosure and constraint of fiber pattern lead to a desired operation. While lots of researches on the actuator has been attributed to linear and bending motions, however, there are only few researches on rotary, or torsional, motions. In this paper, we propose a new actuator that causes azimuthal deformation due to restriction of anisotropically distributed fiber element along the radial direction and expansion of the hyper elastic material. Structure design of the actuator and a fabrication process of the actuator are presented. Subsequently, FEM simulation and experiment are executed to measure rotation angles of the actuators corresponding to the applied pressure.

In this paper, we present a novel framework for quadrupedal stair climbing, which considers force interaction with stairs. For stable and robust climbing, a key issue is to avoid falling down on the stairs. From this point of view, control to minimize rate of change of angular momentum about Center of Mass (CoM) which is produced by ground reaction force (GRF) at contact of robot`s foot is necessary. Using this approach, direct force-based Zero Moment Point (ZMP) for motion planning of the CoM and landing force control are implemented. The direct force-based ZMP method allows the robot to lift its foot with reduced possibility of tilting on the stairs, and the landing force control prevents instant increase of the moment by impact of the GRFs. In addition, terrain recognition to estimate parameters of the stairs and find proper footholds by vision system mounted on the robot is presented. Proposed framework is implemented to quadruped robot, AiDIN-VI, that has torque sensor at each joint, through experiments, capability of ascending several stairs including 3-step stairs which have 21cm height (31% of its maximum leg length) and 26.5° inclination is validated.

This paper presents a 1-link robotic arm that is antagonistically driven by one pair of a high performance super-coiled polymer actuators with an embedded controller. The actuator which is made from Spandex and nylon fibers is low-cost, easy to fabricate and light-weight. Moreover, it can generate large displacement and provide Joule heating capability. The main contribution of the paper is the model-based impedance controller, which enables position control of the antagonistic joint with variable stiffness and damping. The impedance control is a torque-based law, which in turn depends on a proposed backstepping control law to control the force of each actuator. The control system is proved to be stable using dissipativity stability theory and verified through experiments. Experimental results show that our system can track the angular position reference with the worst position error of 0.43deg and root-mean squared error of 0.16deg at steady state for sinusoidal waveform tracking (with the frequency of 0.1Hz), and the worst position error of 0.2deg for set-point regulation.

This paper presents a fabric actuator consisting of ordinary polymer fibers, conductive fibers, and twisted and coiled soft actuators (TCAs). Previous studies have developed a Spandex TCA (STCA) that is driven at a lower temperature than the conventional Nylon TCA and exhibits greater actuation strain. However, no method to drive STCAs via electrical joule-heating has been developed yet. The fabric actuator presented in this paper offers a solution to this problem by employing an STCA multiple fabrication method, a continuous fabrication method, bundling technology, and weaving technology. Two types of samples (cylindrical and planar) are fabricated and their performances are evaluated experimentally. From the actuation test according to the loads, the maximum contraction strain of 34.3% is measured. The repeatability is also verified through 200 cycles of actuation. Using a linearized model, the dynamic performance of the fabric actuator is predicted and compared with experimental results. An actual human arm size mannequin is driven by applying the fabric actuator, and angle control can be achieved with an encoder mounted on the joint. In addition, fabric actuator is weaved to sweater showing the possibility of wearable assistive robot.

From being soft, flexible and producing movement by contracting, soft linear actuators are said to have muscle-like properties. Due to these similarities, they are often called “artificial muscle actuator.” However, the strain produced by these actuators is generally insufficient to be utilized in a large range of applications. Some solutions have been developed, but they sacrifice force to increase the displacement. Meanwhile, the force produced by skeletal muscles increases as it contracts due to its working principle, which is based on the “sliding filament mechanism.” The limitations of soft linear actuators could be overcome by mimicking the contraction process of skeletal muscles. Two types of muscle-inspired robotic joint mechanisms based on the sliding filament mechanism principle are proposed in this work. The mechanisms can be operated using any type of soft linear actuators as well as traditional actuators or motors, and this work realizes the implementation using shape memory alloy wires and 3D printed mechanical parts. The feasibility of both proposed mechanisms, and their capabilities were experimentally verified.

In the physical human-robot interaction system, improving transparency performance which allows humans to move as if there is no robot is a challenging topic. In general physical human-robot interaction, the multiaxial force sensor is used to control the robot. However the signal measured from the force sensor involves not only the force applied to the robot by the human motion intention but also the influence of the natural force feedback between the robot and the human hand due to the motion of the robot. Therefore, in order to improve the transparency performance, it is necessary to consider the dynamics of the human hand as well as the dynamics of the robot. In this paper, an novel algorithm to improve transparency performance is proposed. The proposed algorithm uses only the multiaxial force sensor and compensates the natural force feedback by using the human hand impedance and further improves the transparency performance which has a limitation adjusting admittance parameters. The validity of the proposed algorithm is described through the system model analysis and the experiment using the hydraulic upper limb exoskeleton.

This paper presents a hexapod crawling robot which has bioinspired design and locomotion posture from the insects. The robot, called S-Hex II, is an upgraded version of the different printable monolithic hexapod robot which is named as S-Hex I. The S-Hex II is studied for the project of developing mesoscale walking robots actuated by the soft dielectric elastomer actuators. In comparison with the S-Hex I, the S-Hex II owns smaller dimension, lighter weight, and significantly faster walking speed. We improve and increase the total number of degree-of-freedom (DOF) of the soft dielectric elastomer actuators (DEAs) from three, used in the S-Hex I, up to five, employed in the S-Hex II, and that provides the promising versatile locomotion ability to the S-Hex II robot. This robot has successfully demonstrated the back and forth ambulation on flat surfaces using the alternating tripod gait with the walking speed of 52 mm/s (approximately 0.35 body-lengths per second) at 7 Hz of actuation frequency.

Aiming to apply soft actuators in driving a walking robot, the design, fabrication and locomotion of a bio-inspired printable hexapod robot are studied. The robot mimics the insect's design and walking posture by driving six legs with alternating tripod gait which provides its locomotive adaptability on flat terrains. The versatile movements of the robot's leg are achieved by using soft and multiple degree-of-freedom actuators. The actuators are made by dielectric elastomers with a simple mechanism based on antagonistic configuration. By using 3D printing method, the actuator can be embedded into the frame of the robot and a control system is developed. Finally, the robot's locomotion is successfully demonstrated with variable speeds and stride lengths.

This paper presents a grasper-integrated force sensor that provides the capability of measuring dual axial forces at the tip of surgical robot for minimally invasive surgery (MIS). On the sensorized forceps, the combination of dual axial forces measured at each side of grasper presents three axial pulling and single axial grasping force sensing, which provide force feedback control using haptic device. It consists of simple structure of triangular prism shape and two capacitive-type pressure sensor cells based on elastomeric polymer which provides the information on normal and shear forces. The sensing principle is to compare the difference between responses of two pressure sensors when the surface of the sensor contacts to the tissue. A sensorized forceps is fabricated by employing the molding method and electronics for signal processing is embedded. Finally, experimental evaluations are performed and its feasibility is validated.

This paper presents a preliminary design and experimental results of a multi-axial contact force sensor for robotic surgery graspers. The sensor is a thin-film type capacitive one with a multiple cell structure capable of measuring normal and shear forces at contacts simultaneously. The structure of the sensor is determined via numerical optimization for maximizing sensitivity and based on the results, a prototype is fabricated by employing the silk-screening method. The characteristics of the sensor are evaluated with a multi-axial sensor calibration set-up and the sensitivities for two directional shear forces and a normal forces are measured to be 10.1, 10.3 and 6.1%, respectively. In this study, the feasibility of the sensor is confirmed as the proof-of-concept. In our future studies, a miniaturized pair of the proposed sensor will be embedded to a surgery grasper for in vitro validation.

This paper presents a mechanism for an in-pipe robot, called MRINSPECT VI (Multifunctional Robotic crawler for In-pipe inspection VI), which is under development for the inspection of gas pipelines with 150mm inside diameter. The mechanism is composed of multi-axial differential gear mechanism, wall pressing one, and driven by single motor. It is designed to adapt to the varying inside geometries of pipelines such as elbows by modulating the velocities of active wheels mechanically without any control effort. In this paper, the design features of the mechanism are detailed and its effectiveness is experimentally validated.

The differential drive mechanism, which is one of the mechanisms of wheeled mobile robots, is simple and useful for the motion of the mobile robot. The mechanism, however, has typical disadvantages of losing mobility, falling down, etc. when the robot moves over obstacles or uneven terrains. A novel suspension mechanism presented in this paper was designed to help the robot to overcome these problems. In particular, this mechanism is very suitable for a tall robot, which is susceptible to overturning because of the disturbance caused by acceleration, deceleration, and collision. The proposed mechanism called a Multilayered Suspension Mechanism is composed of the effective and well-directed combination of springs and dampers. It is very simple and cost-effective since it has no actuator for suspension. In this paper, mechanical construction and characteristics of the mechanism are described. Then, excellence and performance of the proposed mechanism are demonstrated by simulations and experiments.

In this paper, we present a smart handheld surgical tool with tactile feedback to help microsurgery. This device consists of force sensors attached to the tool tip and tactile displays on the position of the fingerhold. The sensor is capacitive one and measures not only the magnitude of force, but also the direction of force. The sensor can measure 9N of lateral forces along x-y-z direction. The tactile display is based on dielectric elastomer actuators and made up of three rigid coupling tactile display modules. The tactile displays provide stimuli of 170μm displacement and frequency of 10Hz at the surgeons fingertips. We fabricate the device and its performances are experimentally validated.

Recently, Dielectric Elastomer Actuator(DEA) comes to the market successfully by introducing commercial products such as tactile interfaces for mobile applications. As an advanced application, we present a tactile display device actuated with dielectric elastomer actuator(DEA) in this paper. By employing fluid coupling between the touch spot and the actuator, the device ensures the comfort of touch and the safety of operation from the high driving voltage while contacting with the human skin. In addition, it is compatible with SMT(Surface Mount Technology), which can be easily plugged into PCB(Printed Circuit Board)s like semiconductor chips and extend to the arrayed tactile display, easily. In this paper, its working principle is overviewed and the actual design with fabrication procedures are described in details. Finally, a prototype is made and its performance is evaluated experimentally.

This paper presents a comprehensive study on the design and implementation about 2-DOF decoupled kinematic actuator module based on the parallel structure with a high mechanical stiffness. The basic structure of 2-DOF decoupled kinematic actuator module has two motion units. Since one motion unit can be moved in only one direction, various applications are available and it can solve the parasitic motion fundamentally. The two motion units also have fine motion and coarse motion respectively. Besides it can be variously modified based on how the actuators are connected. Then the hardware of 2-DOF decoupled kinematic actuator module is implemented with one actuator and two additional locking devices. And the performance of the hardware will be evaluated by experimental system.

The curvatures of an object play an important role in the shape reconstruction of that object. In this research, we suggest a method of estimating unknown curvatures using a coarse-resolution force torque sensor. First, a method of estimating unknown curvatures using large motions in terms of rolling and sliding is proposed. Next, a tracking algorithm for an unknown surface based on an inner position loop control algorithm is presented. An application of this method to the finger of a robot hand is also discussed. Finally, the algorithm is verified by simulations and experiments for several cylinders with different radii.

In this paper, we present a global localization and local pose error compensation method in a known structured environment using magnetic landmarks. In previous our research, it was possible to compensate the pose error (xe, ye, qe) of a mobile robot correctly on the surface of structured environment with magnetic landmarks. In this work, we propose a methodology of arranging magnetic landmarks on the map such that properly arranged magnetic patterns ease the global localization of a mobile agent. Among total six patterns of magnetic-bar in square arrangement, five unique landmarks are obtained. Therefore, a heuristic pattern search method is applied to build the virtual map using five landmarks. In order to obtain the global pose information, the robot identifies the pattern of magnets, and obtains the current global pose information by comparing the measured neighboring patterns with the map information that is saved in advance. Experimental results show the effectiveness of the magnetic-pattern landmarks for the global localization and local pose control of a mobile robot.

In this paper we present a robotic actuation system by artificial muscle actuator based on dielectric elastomer. A novel linear actuator called “multi-stacked actuator” is presented, which can be embedded in the phalanges of the finger and ensures a compact design of the overall system. As an exemplary work, a two degree-of-freedom robot finger is developed and its performance is experimentally demonstrated. The proposed system can be extended to the multi-fingered robot hand easily, and applied even for articulated mechanisms such as legged robots etc.

Physical size of semiconductor components has been reduced and device density has become increased especially during for last years. As a result of this the use of various high precision manipulatable robot systems becomes norm in the industry. Normally the high precision robot system consists of precision staging system, small scale end-effector system, and highly sensitive autonomous sensing system. One of the most popular micromanipulation tasks might be handling of micro-scale objects on a surface. Although many functional aspects and constraints should be considered when the system is constructed, a key concern for the system design is level of dexterity of the manipulator especially when size of the objects to be handled and spatial resolution of the manipulator become smaller than micron or nano scale. And stiction effect has appeared since a micro-contact mechanics phenomena affects more primarily than inertial force in the high precision robot system. Thus a theoretical study has to be developed on a micro-contact mechanics phenomena. In this paper, the organized system is equipped with an omnidirectional accessible manipulation system with a new visual feedback system. Thanks to the enhanced dexterity of the system, in this paper, microparticle stiction problems that could happen to most of small object handling also can be resolved.

As a major human sensory function, the implementation of the tactile sensation for the human-machine interface has been one of the core research interests for long time. In this paper, an innovative tactile display device based on the soft actuator technology is presented. Using electroactive polymer for the construction of the tactile display device, it can provide stimulation on the human skin without any additional electromechanical transmission. Softness and flexibility of the device structure, ease of fabrication, possibility for miniaturization, and low cost for mass production are the representative benefits of the presented device. Especially, the device application is open to many different purposes since the flexible structure offers the excellent adaptability to any contour of the human body. To prove its feasibility, a wearable device that can fit to the distal part of the human finger is presented and its performance is evaluated, experimentally.

In this paper, we present a new artificial muscle actuator for the robotic applications, called multi-stacked actuator. This actuator is made from a new material, named synthetic elastomer previously developed by ourselves. The synthetic elastomer displays enhanced performance in terms of electrical as well as mechanical properties, which can be adjusted depending on its applications. The actuator is composed of the synthetic elastomer sheet coated with compliant electrodes on the both sides, connecting disks, spring, and rigid frame. This novel design enables the actuator to generate the large strain as well as the large force. Experimental works are performed to evaluate the actuation performance and the effectiveness of the actuator is validated.

Tactile sensation is one of the most important sensory functions for human perception of objects. Recently, there have been many technical challenges in the field of tactile sensing as well as tactile display. In this paper, we propose an innovative tactile display device based on soft actuator technology with electroactive polymer (EAP). This device offers advantageous features over existing devices with respect to intrinsic flexibility, softness, ease of fabrication and miniaturization, high power density, and cost effectiveness. In particular, it can be adapted to various geometric configurations because it possesses structural flexibility, so it can be worn on any part of the human body such as finger, palm, and arm etc. It can be extensively applied as a wearable tactile display, a Braille device for the visually disabled, and a human interface in the future. A new design of the flexible actuator is proposed and its basic operational principles are discussed. In addition, a tactile display device with 10times10 actuator array (100 actuator cells) is developed and its effectiveness is confirmed

Tactile sensation is one of the most important sensory functions along with the auditory sensation for the visually impaired because it replaces the visual sensation of the persons with sight. In this paper, we present a tactile display device as a dynamic Braille display that is the unique tool for exchanging information among them. The proposed tactile cell of the Braille display is based on the dielectric elastomer and it has advantageous features over the existing ones with respect to intrinsic softness, ease of fabrication, cost effectiveness and miniaturization. We introduce a new idea for actuation and describe the actuating mechanism of the Braille pin in details capable of realizing the enhanced spatial density of the tactile cells. Finally, results of psychophysical experiments are given and its effectiveness is confirmed.