• Abstract

This paper proposes a generalized method for designing tendon-driven serial-chained manipulators with an arbitrary number of tendon redundancy. First, a special class of tendon-driven structures is defined by introducing the controllable block triangular form (CBTF) of a null space matrix and its complementary CBTF of a structure matrix, satisfying physical constraints related to the minimal connection of tendons and to the placement of actuators. Then it is shown that any general design of tendon-driven serial manipulators can be reduced to the design of such a special class of tendon-driven structures. Two associated design problems are derived and solved. The first design problem is about finding a complementary CBTF structure matrix for a given CBTF null space matrix using algebraic relations, whereas the second one seeks the both matrices that optimize the wanted structural characteristics based on the result of the first design problem. Numerical design examples are provided to show the validity of the proposed method.

• Abstract

This paper introduces a new development of a two-wheeled robotic wheelchair (TWW), designed to address the challenges of personal mobility for the elderly and individuals with lower limb disabilities. By incorporating a sliding seat mechanism and motorized support legs, the TWW enhances stability, comfort, and accessibility in narrow or uneven environments. Notably, the TWW has a minimum turning radius of 0.372[m], enhancing convenience in confined spaces. A dynamic inversion-based motion planner is developed to provide smooth and stable driving experiences by accurately converting user inputs into optimal trajectories. Furthermore, the system prioritizes safety through real-time fault detection, ensuring reliability in various scenarios. Experimental results validate the system’s enhanced posture stability and safety, highlighting its potential for a wide variety of applications in daily mobility and rehabilitation support.

• Abstract

Human–robot collaboration (HRC) is becoming a key element in next-generation automated manufacturing and assembly, but physical human–robot interaction (pHRI) in such settings is still mostly restricted to simple, low-level contacts. This work proposes a deep-learning-based pHRI framework in which predefined human touch gestures are used as intuitive communication cues for collaborative tasks. A touch-gesture recognition network is built on a gated recurrent unit (GRU) architecture and is trained on ground-truth dynamic responses of a robot manipulator—namely energy variation, generalized momentum, and external joint torques—generated by known touch gesture types applied to different robot links. The network jointly identifies five representative touch gesture classes and the associated robot link, yielding 35 possible outputs, and achieves 96.94% recognition accuracy on the collected dataset. Experiments analyze how recognition performance depends on gesture type and intensity, highlighting the behavior and strengths of the proposed model. An IKEA chair assembly scenario is further presented to illustrate how the recognized touch gestures can be employed in a real collaborative task. Overall, the study demonstrates that leveraging touch gestures as a learned modality can promote physical interaction to a central role in communication for practical HRC applications.

• Abstract

In robotic manufacturing, connector assembly poses challenges due to misalignment, jamming, insufficient insertion force, and potential damages of robot and connector. To overcome these issues, we propose a robot gripper that emulates human’s connector assembly strategy where rotational force and linear force are superimposed. Utilizing a statics model, we adjust the parameters (rotation angles, cycle time, insertion forces, etc.) to optimize the assembly tasks that employ the proposed gripper. The developed gripper structure is capable of precise rotational control synchronized with adaptive impedance control of the manipulator in the direction of the assembly. Experiments demonstrate that our gripper reduces insertion time, decreases required force, and enhances stability, preventing jamming and wedging phenomena. This approach can improve efficiency and reliability in robotic connector assembly while minimizing damages to manipulators and connectors.

• Abstract

Vertically aligned carbon nanotubes (VACNTs) exhibit outstanding mechanical strength, chemical stability, and electrical characteristics; however, their constrained mechanical elasticity and chemical responsiveness spurred research on atomic decoration techniques for enhancing their mechanochemical attributes. Nevertheless, achieving uniform atomic decoration on the VACNT surface is difficult because of the high density and large aspect ratio of VACNT. Herein, a strategy to design and apply nanopatterned VACNTs (nVACNTs) based on a nanotransfer printing process is proposed to improve atomic penetrability. Nanopatterns inherent to nVACNTs facilitate atomic penetration, allowing for the more consistent and higher quality deposition of functional materials such as zinc oxide and alumina by atomic layer deposition. Furthermore, physical vapor deposition provides an improved coating of metal catalysts such as gold. The uniform deposition of ceramic layers on the entire surface of nVACNTs strengthens its mechanical resilience, owing to the diminished van der Waals forces of CNTs. Surface-decorated nVACNTs display an increased sensitivity to NO2 gas, which is attributed to the enhanced quality of the reactive catalyst deposition and augmented permeability. This strategy achieves a larger decorated area while increasing a catalytically active reaction area. The obtained results promise that the enhanced nVACNTs will expand the industrial applications of carbon nanotubes.

• Abstract

Wheels have been commonly used for locomotion in mobile robots and transportation systems because of their simple structure and energy efficiency. However, the performance of wheels in overcoming obstacles is limited compared with their advantages in driving on normal flat ground. Here, we present a variable-stiffness wheel inspired by the surface tension of a liquid droplet. In a liquid droplet, as the cohesive force of the outermost liquid molecules increases, the net force pulling the liquid molecules inward also increases. This leads to high surface tension, resulting in the liquid droplet reverting to a circular shape from its distorted shape induced by gravitational forces. Similarly, the shape and stiffness of a wheel were controlled by changing the traction force at the outermost smart chain block. As the tension of the wire spokes connected to each chain block increased, the wheel characteristics reflected those of a general circular-rigid wheel, which has an advantage in high-speed locomotion on normal flat ground. Conversely, the modulus of the wheel decreased as the tension of the wire spoke decreased, and the wheel was easily deformed according to the shape of obstacles. This makes the wheel suitable for overcoming obstacles without requiring complex control or sensing systems. On the basis of this mechanism, a wheel was applied to a two-wheeled wheelchair system weighing 120 kilograms, and the state transition between a circular high-modulus state and a deformable low-modulus state was realized in real time when the wheelchair was driven in an outdoor environment.

• Abstract

In this paper, we propose a highly reliable and accurate collision estimator for robot manipulators working in human–robot collaborative environments, based on the Bayesian approach for practical uses. We assume the robot collision as a dynamic Markov process, not a static event, to reflect the transient behavior of mechanical collisions. Thus, the collision estimator can integrate the prior belief on collision and the measurements on the robot state, to produce the current belief on the robot collision in a usual recursive form. An exponential form of observation model, serving as the likelihood function, is constructed on the projected observation domain by using the multi-variate statistical information of empirical models of collision and non-collision cases. The proposed method is validated by using a commercial 7 degree-of-freedom (DOF) collaborative robot arm with random impacts along the links while it is in motion. Results show that the proposed collision estimator achieves a compelling performance with collision estimation time of 8.86ms on average, an overall accuracy of 99.47%, and zero occurrence of false alarm.

• Abstract

In this paper, we introduce a recently built screwing robotic system for the bolt assembly of elastic steel plates. The screwing robotic system consists of two vision cameras (having narrow and wide fields of view), a collaborative robot with a 10 kg payload, and a motorized screw drill with a pneumatic bolt supplier. Due to the elasticity of the steel plates, they tend to statically deform and dynamically vibrate during tasks under the conventional setting of automatic screwing, often resulting in screw failures. Thus, we designed a compliant connector device to be attached between the robot end-effector and screw drill that can absorb vibration and shock during the bolt assembly to improve the screwing quality and success rate of the bolt assembly. Upon adopting this screwing robotic system with the compliant connector, the success rate of the bolt assembly was improved from 56% to 100%.

• Abstract

This paper presents the control of a rescue robot driven by the worm-wheel gear transmission. In the modeling process, the load-dependent friction of the worm-wheel gear is considered, and the governing equations for static and dynamic analyses are formulated. Especially we examine the dependency of break-in joint torques on the loading torque and directionality of motion. The friction parameters of the worm-wheel gear of a physical rescue robot are identified through experimental investigation. A friction compensation controller is then designed based on the modeling results and experimental operating conditions. And the designed controller is applied to a dual-arm rescue robot to validate its effectiveness.

• Abstract

This paper presents a real-time trajectory planning method for highly dynamic tracking control of wheeled inverted pendulum (WIP) systems. A generic form of dynamic inversion problem for the class of WIPs is defined by combining a set of kinematic and dynamic differential constraints related to the system’s output expressed by the state variables, whose time evolution is to be sought as the solution of the trajectory planning. Instead of simply integrating forward the set of differential equations, which would lead only to an unbounded solution due to its non-minimum phase nature, an asymptotic expansion technique, transforming the original differential equations into a sequence of algebraic equations parameterized by the system’s characteristic constant, is used to allow for a stable and asymptotically exact solution of the dynamic inversion problem. To implement the proposed method for a real-time application where the reference command is not previously known, a command input filter is designed and applied to adjust the real-time input into a sufficiently differentiable reference command suitable for the inversion. Simulation and experimental studies are provided to validate the proposed method using our experimental WIP system.

• Abstract

This study introduces a smart wrist band system with pressure measurements using wrist skin curvature variation due to finger motion. It is easy to wear and take off without pre-adaptation or surgery to use. By analyzing the depth variation of wrist skin curvature during each finger motion, we elaborated the most suitable location of each Force Sensitive Resistor (FSR) to be attached in the wristband with anatomical consideration. A 3D depth camera was used to investigate distinctive wrist locations, responsible for the anatomically de-coupled thumb, index, and middle finger, where the variations of wrist skin curvature appear independently. Then sensors within the wristband were attached correspondingly to measure the pressure change of those points and eventually the finger motion. The smart wrist band was validated for its practicality through two demonstrative applications, ie, one for a real-time control of prosthetic robot hands and the other for natural human-computer interfacing. And hopefully other futuristic human-related applications would be benefited from the proposed smart wrist band system.

• Abstract

In this paper, a two-way self-adaptive gripper that has adaptability to external disturbance loads during linear opening/closing pinch actions and adaptability to encompass a variety of shapes during grasping using a single actuator is proposed, unlike the previous self-adaptive robotic grippers capable of only shape adaptation. Therefore, both linear motion adaptability and shape adaptability during parallel grasping situations are enabled by the proposed design of the gripper. Adaptation to the linear pinch motion is provided through the use of a differential gear, the two outputs of which drive the two tips of the gripper. If facing uneven external loads, the differential gear adaptively alters the speeds of the two outputs, resulting in different closing speeds of the two gripper tips. Despite asymmetric closing, very stable grasping can be guaranteed for such a situation. The differential gear can even complete the grasping by intentionally or unintentionally fixing one of the gripper tips. The proposed design is also capable of shape adaptation in the encompassing grasping mode by adopting a parallel-linkage gripper mechanism, consisting of an exoskeleton and 6 internal joints with a spring element. The finger exoskeleton facilitates pinch and spread actions, while the encompassing action is carried out by adjusting the internal linkage. Based on the kinematic analysis and modeling of the proposed gripper, a prototype of the two-way adaptive gripper hardware was developed. Several experiments were performed to verify the feasibility and validity of the proposed gripper system. The actuator using the proposed differential gear was shown to be able to grasp objects in jammed conditions. In addition, the gripper was able to perform grasping actions, such as pinch, spread, and encompassing grasp.

• Abstract

We propose a method that computes an inverse solution of the wheeled inverted pendulum (TWIP) for trajectory tracking problem using singular perturbation principle. We observe that the TWIP shows a combined slow and fast behaviors during motion, where the slow motion is the gross motion of the TWIP while the fast motion is the pitch motion of the TWIP itself. The singular parameter, which separates slow and fast parts of dynamics, is defined by pendulum’s mass and length parameters. The proposed method considers dynamic and kinemaitc constraints, parameterized with the singular parameter defined, with appropriate boundary conditions to obtain a consistent solution that is mathematically expressed by infinite series. Details of the solution method is presented and validated via experimentation with linear and circle tracking tasks.

• Abstract

This article proposes a novel differential kinematics of elastic tendons for tendon-driven manipulators where tendons transmit actuator force/torque to remote links via a train of pulleys. The local variability of tension and longitudinal speed in each tendon is carefully investigated in terms of the rest lengths of the virtually partitioned tendon segments along the tendon. A significant attention is paid to building a proper friction-tension mechanic model between the pulleys and tendons to identify the no-slip points that are important to be used as kinematic constraints. The kinematic relations of tendon are obtained for two possible types of tendon-pulley transmission, i.e., free-free ended and fixed-free ended types, and then a complete kinematics of tendon is formulated by augmenting all the kinematic relations existing in the entire system. Simulation and experimental results are provided to validate the proposed kinematics of tendon by comparing with a previous simple spring model where the tension was determined by the relative positions of consecutive pulleys.

• Abstract

Robotic hands perform several amazing functions similar to the human hands, thereby offering high flexibility in terms of the tasks performed. However, developing integrated hands without additional actuation parts while maintaining important functions such as human-level dexterity and grasping force is challenging. The actuation parts make it difficult to integrate these hands into existing robotic arms, thus limiting their applicability. Based on a linkage-driven mechanism, an integrated linkage-driven dexterous anthropomorphic robotic hand called ILDA hand, which integrates all the components required for actuation and sensing and possesses high dexterity, is developed. It has the following features: 15-degree-of-freedom (20 joints), a fingertip force of 34N, compact size (maximum length: 218 mm) without additional parts, low weight of 1.1 kg, and tactile sensing capabilities. Actual manipulation tasks involving tools used in everyday life are performed with the hand mounted on a commercial robot arm.

• Abstract

In this paper, we propose a robust method for estimating the parameters of robot manipulators using the torque separation technique, which was developed previously by the authors, to extract the inertial, gravitational, and frictional components from the input torques of multiple sinusoidal joint motions. The separated components of the input torque produce a set of reduced linear regression equations where the dynamic parameters of the robot manipulators appear decoupled or minimally coupled. A mathematical analysis is presented to show that the set of reduced regression equations tends to yield more robust parameter estimation than the conventional way where a large dimensional full regression equation is solved simultaneously. An iterative scheme to alleviate the possibility of parameter estimation error caused by the deviation from the assumed ideal sinusoidal motions is also proposed. Experimentation with two robot manipulators is used to verify the proposed approach and related claims. The proposed method is simple and pragmatic without requiring any specialized signal filtering and technical know-hows which numerous previous methods often demanded for explicitly or implicitly.

• Abstract

Significant attention has been paid to robotic rehabilitation using various types of actuator and power transmission. Amongst those, cable-driven rehabilitation robots (CDRRs) are relatively newer and their control strategies have been evolving in recent years. CDRRs offer several promising features, such as low inertia, lightweight, high payload-to-weight ratio, large work-space and configurability. In this paper, we categorize and review the cable-driven rehabilitation robots in three main groups concerning their applications for upper limb, lower limb, and waist rehabilitation. For each group, target movements are identified, and promising designs of CDRRs are analyzed in terms of types of actuators, controllers and their interactions with humans. Particular attention has been given to robots with verified clinical performance in actual rehabilitation settings. A large part of this paper is dedicated to comparing the control strategies and techniques of CDRRs under five main categories of: Impedance-based, PID-based, Admittance-based, Assist-as-needed (AAN) and Adaptive controllers. We have carefully contrasted the advantages and disadvantages of those methods with the aim of assisting the design of future CDRRs.

• Abstract

In this paper, we propose a multi-sensor-based collision detection algorithm for free and contact situations. The important characteristics of this collision detection algorithm include correctness, fast detection, and versatility. An appropriate combination of suitable multiple sensors such as encoders, force/torque sensors, and accelerometers can be used to improve the proposed collision detection algorithm in terms of these characteristics. Moreover, the dynamic parameters of a robot manipulator must be modeled accurately to obtain better estimates of any possible torque deviation caused by a collision. We employ the torque separation technique that allows us to estimate the dynamic parameters separately, and thus, to increase the robustness of parameter estimation. A momentum-residual-based collision observer with additional information from a force/torque sensor and a set of accelerometers is designed to enhance collision detection. When a robot manipulator holds an object, the effect of the object on the robot dynamics should be considered by using force/torque sensor information. The reactivity of collision detection time and the identifiability of blind spots and collision directions are enhanced using cheap accelerometers. The proposed algorithm is verified by employing a six-axis industrial robot manipulator.

• Abstract

In this work, structural synthesis of lower-mobility cable-driven parallel mechanisms (CDPMs) is conducted to clearly identify all feasible structures of the lower-mobility CDPMs with n-degrees-of-freedom, which are driven by n +1 cables fixed on the ground. Through the synthesis, geometric information of various and some new promising structures of unconstrained and constrained lower-mobility CDPMs such as actuation cable wrenches, cable position vector, and required constraint wrenches, are successfully extracted. Then a promising 3T1R type CDPM structure is selected to develop as a haptic device. Its position analysis is conducted and its input-to-output force model is derived. Also, its feasible workspace and its input-to-output force transmission characteristics are examined. Then a prototype haptic device is implemented which is controlled by Raspberry Pi microprocessors. Through a virtual wall following operation by the operator, its operational capability as a haptic device is verified.

• Abstract

Industrial robot identification is usually based on the inverse dynamic identification model (IDIM) that comes from Newton's laws and has the advantage of being linear with respect to the parameters. Building the IDIM from the measurement signals allows the use of linear regression techniques like the least-squares (LS) or the instrumental variable (IV) for instance. Nonetheless, this involves a careful preprocessing to deal with sensor noise. An alternative in system identification is to consider an output error approach where the model's parameters are iteratively tuned in order to match the simulated model's output and the measured system's output. This paper proposes an extensive comparison of three different output error approaches in the context of robot identification. One of the main outcomes of this work is to show that choosing the input torque as target identification signal instead of the output position may lead to a gain in robustness versus modeling errors and noise and in computational time. Theoretical developments are illustrated on a six degrees-of-freedom rigid robot.

• Abstract

In this paper, a new kinematic calibration method that takes into consideration the effect of joint compliance in robot manipulators is proposed. A modified product-of-exponential (POE) kinematic model is formulated in such a way that it accommodates static joint deflection by gravitational force. A novel nonlinear cost function is constructed by combining the modified POE kinematic model and the end point measurements of the deflected circular trajectory, so that the kinematic screw and joint compliance are simultaneously identified after minimizing the cost function. An in-depth discussion of how to select a good reference configuration for better parameter identification is also given. Simulation and experimental results are provided to demonstrate the effectiveness of the proposed kinematic calibration method for an industrial 6-DOF (degree-of-freedom) robot manipulator and a custom 9-DOF robot manipulator.

• Abstract

We present a novel technique for 3D point cloud simplification — the so-called fractal bubble algorithm — to minimize the computational time and overall storage space. The proposed fractal bubble algorithm generates 2D elastic bubbles and copies of themselves through 2D data sets representing planar geometric contours. Each of the bubbles, as it grows, is made to select a single point of its first contact, and all the selected points become the simplified set of points. The fractal bubble algorithm is repeatedly applied to the simplification of planar slices of general 3D point clouds corresponding to 3D geometric objects, leading to the global simplification of 3D point clouds. The benefits of the algorithm are: first the algorithm is computationally light and memory efficient, second it is simple to implement and inherently allows the organized selection of the points of contact and finally it enables us to simplify the point cloud data through a multi-scale fashion by varying a set of user-controlled algorithm parameters. Numerical results verify the effectiveness of the proposed algorithm.

• Abstract

A numerically efficient force distribution method for actuator saturation avoidance is proposed, which is applicable to two different types of the mechanisms with two degrees of actuator redundancy, parallel mechanism (PM) and cable-driven parallel mechanism (CDPM). The proposed method searches the optimal force solutions based on their geometric interpretation. Each actuator force with two degrees of actuator redundancy is expressed as a plane equation with respect to two intermediate variables. Thus, the optimal forces are found by searching for both the intersections between force planes and the common intersection points among those force planes. The proposed method for each of PM and CDPM is described. Then for two different exemplary mechanisms, the 2T2R -type 4 -DOF CDPM with six actuation cables and for the 2T1R -type planar 3- DOF PM with five active joints, comparative simulations moving along the spiral trajectory are conducted, employing three different methods, the proposed method and the other two typical off-line methods, the interior point method and the linear matrix inequality method. It is confirmed from those simulation results that the computational efficiency of the proposed method in finding their desired optimal force solutions is superior to the ones of the other two typical offline optimal searching methods and also sufficiently fast enough in real time applications.

• Abstract

This paper proposes a new antagonistic tendon-driven joint (TDJ) that exhibits higher stiffness and larger travel range than conventional types of TDJs. A detailed mathematical analysis of the stiffness of the proposed TDJ is conducted and compared to other TDJs. The effect of the tendon length is taken into consideration to establish a more precise and realistic stiffness model of the proposed TDJ. Thereafter, two hardware prototypes of the proposed TDJ design, developed in the form of a packaged modular structure that integrates two TDJs, are introduced. Using these prototypes, the stiffness characteristics of the proposed TDJs are verified through experimentation. Additionally, experimental results on the stiffness behavior during the mimicked needle insertion tasks are provided. Results show that the proposed TDJs present much higher stiffness than conventional ones and thus give a potential benefit to precision manipulation.

• Abstract

In this paper, dynamic modeling and control of small scale wire driven robotic joints (WDRJ) with elastic wires is studied in detail. In the dynamic modeling, it is assumed that the dominant dynamics of wires which are the longitudinal vibrations of the wires can be approximated by a linear axial spring model. Moreover, the dynamic model of the WDRJ is converted to the standard form of singular perturbation, which allows the controller design on the base of the singular perturbation theory. The proposed control scheme consists of two major parts, slow and fast sub-controllers. First, a slow sub-controller is designed by considering WDRJ with ideal rigid wires, which is used to control the gross motion of the WDRJ. Then, this controller is extended to the WDRJ with elastic wires by adding the fast sub-controller, to counteract the longitudinal vibrations caused by the inevitable elasticity of the wires. Furthermore, to ensure all the wires remain in tension, the proposed control strategy is refined by adding the concept of internal force. Finally, the efficiency of the proposed control algorithm is investigated through simulations. And it is demonstrated that WDRJ is an appealing candidate for the design of small scale robotic system.

• Abstract

In this work, a revolute joint-based asymmetric Schönflies motion (SM) haptic device with 4-Degree-of-Freedom (DOF) force feedback capability is developed. The SM haptic device is composed of a redundantly actuated parallel sub-module which has translational 3-DOF output motion, a pantograph limb which takes the role of providing 1-DOF rotational output motion, and a revolute joint allowing the relative motion between them. All five DC motors without gearhead are placed on the ground by employing proper parallel transmission linkages for power transmission. The large singularity-free workspace and the improved kinematic characteristics are secured by redundantly actuating the 3-DOF sub-module. Thus, the SM haptic device has excellent features such as the unlimited 1-DOF rotational output motion, minimal friction, minimal inertia, and large dexterous workspace. Mobility analysis, kinematic modeling, singularity analysis, optimal design, and linear inertia modeling of the SM haptic device are conducted. Then a prototype with two operational modes such as gravity compensation and linear inertia compensation modes is implemented. Through friction measurements, motion tests for gravity and/or linear inertia compensation modes, and virtual wall experiments, it is confirmed that the prototype possesses minimal friction as well as good gravity and linear inertia compensation performances sufficient for the high-quality haptic device applications such as medical training, robot-assisted surgery, etc.

• Abstract

This article proposes a sequential optimization approach to efficiently identify non-minimal dynamic parameters of robot manipulators, possibly having large degrees of freedom. A back-substitution-based parameter identification from the last link to inward links is enabled due to the block upper triangular form of inherent regressor matrix. Starting with the dynamic model using the non-minimal parameters, we derive a generic compact formulation for the linear regression equation. We then establish a sequential optimization procedure taking into account physical feasibility of parameters. Numerical case examples demonstrate the validity of the proposed approach.

• Abstract

In this paper, we present a study on the development of the manufacturing process of thrust washers for an automobile. The thrust washers are manufactured using the progressive cold forging method. The proposed progressive cold forging method requires less manufacturing cost and processing time compared with the previous conventional manufacturing method, through the elimination of some cutting and grinding processes. The proposed cold forging method uses the single plate material that is used in multi-step forging process (progressive method). In order to estimate the plastic deformation of the product due to cold forging, we conduct a finite-element analysis and compare the predicted deformation with the experimental results. The effectiveness of the proposed manufacturing process is verified by comparing the simulation and experimental results. Finally, we suggest a new stereotyped design of the single plate type cold forging process, based on the data obtained by performing simulation and experiments.

• Abstract

In this paper, we present the dynamic modeling and controller design of a tendon-driven system that is antagonistically driven by elastic tendons. In the dynamic modeling, the tendons are approximated as linear axial springs, neglecting their masses. An overall equation for motion is established by following the Euler-Lagrange formalism of dynamics, combined with rigid-body rotation and vibration. The controller is designed using the singular perturbation approach, which leads to a composite controller (i.e., consisting of a fast sub-controller and a slow sub-controller). An appropriate internal force is superposed to the control action to ensure the tendons to be in tension for all configurations. Experimental results are provided to demonstrate the validity and effectiveness of the proposed controller for the antagonistic tendon-driven system.

• Abstract

In this study, we propose a technical method — the so-called dynamic superposition method — for separation of dynamic terms of robot manipulators. We lay over a set of dynamic responses from sinusoidal joint trajectories of different cyclic frequencies, so as to disassemble pure inertial, gravitational and/or frictional torques from the full dynamics forces. The benefits are: first to help us identify dynamic parameters in a simpler sequential manner with better reliability, and second to enable us to understand the in-depth dynamic nature of a specific robot system through dissection. Experimental results confirm the effectiveness of the proposed method.

• Abstract

In this paper, we propose a method of iterative proportional-integral-derivative parameter tuning for mechanical systems that possibly possess hidden mechanical resonances, using a parameter chart which visualises the closed-loop characteristics in a 2D parameter space. We employ a hypothetical assumption that the considered mechanical systems have their upper limit of the derivative feedback gain, from which the feasible region in the parameter chart becomes fairly reduced and thus the gain selection can be extremely simplified. Then, a two-directional parameter search is carried out within the feasible region in order to find the best set of parameters. Experimental results show the validity of the assumption used and the proposed parameter tuning method.

• Abstract

In this study, a new 5-degree of freedom parallel-type robot for neurosurgery is developed and investigated for potential application in deep brain surgery (DBS). The neurosurgical robot consists of the base plate, the moving plate, and three limbs (a PPPU type central limb and two SPS type side limbs) connecting the plates. With an intension to use the developed neurosurgical micro robot with a macro scale robot, the position and kinematic analyses of the macro–micro robot are conducted. A structural analysis under the maximum payload condition is also conducted to confirm its structural rigidity. Then, a macro–micro robot simulator that employs the prototype as a micro robot module is developed to test both its motion capability and its potential application as a stereotactic DBS device. Finally, the absolute position accuracy measurement of the developed micro robot module based on its identified kinematic calibration model verified that its accuracy is comparable to those of existing micro robot module candidates.

• Abstract

In this paper, we propose a new type of active variable stiffness actuator (VSA) by using a unique differential worm gear mechanism where a set of compressible coil springs are installed. The stiffness of the VSA is varied depending on the compressed amount of the coil springs; large compression results in an effectively stiff joint, and vice versa (compliant mode). Interestingly, an ideal rigid joint is also realizable if the springs' reactive force is made larger than the external load (rigid mode). The VSA is characterized to become compliant rapidly if the external load exceeds the springs' reactive force, so such a VSA can protect itself in an unexpected overloading condition. Conducted experiments confirm the effectiveness of the proposed VSA.

• Abstract

This paper addresses a unified formulation of dynamics of general class k(k = 1,2,…,) tensegrity systems using nonminimal coordinates in a matrix form. The dynamics are described by a matrix differential equation with a set of linear constraints, yielding a compact and simplified form. A reduced form of the dynamics is also provided by embedding the linear constraints to the full-order dynamics.

• Abstract

In this paper, we propose a virtual joint method that better utilizes quasi-velocities for the kinematic modeling of wheeled mobile manipulators. By identifying quasi-velocities as motions of imaginary revolute and prismatic kinematic pairs, our method enables one to regard a mobile manipulator as an ordinary articulated manipulator for the purposes of velocity analysis. We also propose an inverse kinematic scheme for the mobile manipulators along the line with the virtual joint based kinematic framework. Details are worked out for mobile manipulators with representative differential-drive and car-like mobile platforms.

• Abstract

In this paper, we propose a virtual joint method that better utilizes quasi-velocities for the kinematic modeling of wheeled mobile manipulators. By identifying quasi-velocities as motions of imaginary revolute and prismatic kinematic pairs, our method enables one to regard a mobile manipulator as an ordinary articulated manipulator for the purposes of velocity analysis. We also propose an inverse kinematic scheme for the mobile manipulators along the line with the virtual joint based kinematic framework. Details are worked out for mobile manipulators with representative differential-drive and car-like mobile platforms.

• Abstract

This paper provides a numerical correction algorithm for implementation of the dynamics of tensegrity systems described by non-minimal coordinates. This correction algorithm corrects any numerical error that would violate the fixed-length bar constraints. A recursive form of the correction algorithm is proposed, and simulation results support the validity of the proposed scheme.

• Abstract

Our two-fold purpose was (i) to quantitatively identify characteristic vectors, i.e., specific combinations of joint angles of fingers, that dominate the posture variation of precision grips in the configuration space (the space with joint variables of the fingers in the hand), and (ii) to investigate linear correlations between the postural variation and the object size using the parameters of the characteristic vectors. Experiments involving 14 participants measured the grip postures of the participants who were asked to grasp eight cylindrical objects of different diameters using six designated precision grips (spherical, tripod, pinch, quad-pinch, tri-pinch, and mini-pinch). Regression analysis showed that within each precision grip, the postures changed gradually in a unique linear direction in the configuration space with an increasing object size relative to the hand size. Quantitative models of the precision grips were established that could be used to reproduce the precision grip postures for grasping various object sizes by adults of various hand sizes.

• Abstract

We propose an approach for the exact dynamic inversion of singularly perturbed second-order linear systems through asymptotic expansion in a singular parameter. We show that the inversion solution, corresponding to the invariant slow manifold, can be expressed as a converging infinite series under desired output constraints composed of exponential support functions in the complex domain. We provide systematic mathematical procedures to obtain the closed-form invariant slow manifold, along with required admissible boundary conditions. Numerical examples are given to validate the proposed approach.

• Abstract

In this paper we propose an intuitive and practical grasp quality measure for grasping 3D objects with a multi-fingered robot hand. The proposed measure takes into account the object geometries through the concept of object wrench space. Physically, the positive measure value has a meaning of the minimum single disturbance that grasp cannot resist, while the negative measure value implies the minimum necessary helping force that restores a non-force-closure grasp into a force-closure one. We show that the measure value is invariant between similar grasps and also between different torque origins. We verify the validity of the proposed measure via simulations by using computer models of a three-fingered robot hand and polygonal objects.

• Abstract

A novel predictor-corrector hold (PCH) that yields continuous estimates for all instances is proposed for multi-rate control systems. The principle, characteristic, and performance of the PCH are analyzed. Through a comparison with other conventional holds, the efficacy of the proposed PCH is validated.

• Abstract

This paper describes a new trajectory planning method for the output tracking control of linear flexible systems; this method computes the exact solution of the equilibrium manifold. We establish a system of differential equations by combining kinematic and dynamic constraints and reformulate them in a singularly perturbed dynamics to obtain the equilibrium manifold in the form of an infinite series, which is our planned trajectory. We show that for the desired output defined by exponential functions, the equilibrium manifold becomes a converging geometric series that has a succinct form of summation. In addition, the inverse torque, which is the feedforward command, is easily produced by using the computed exact equilibrium manifold. We validate the effectiveness of the proposed method through simulations and experimental studies using a single-link flexible arm.

• Abstract

A 2× 2 block matrix inversion is a tool that is frequently used in areas of control, estimation theory and signal processing. However, one of the two diagonal entries of the block matrix should be invertible to carry out a conventional block matrix inversion. In this technical note, we show that this assumption can be partially released with three new types of symbolic block matrix inversion. Also, an application example of an inverse plant model of a multi-inputs and multi-output (MIMO) plant, which cancels plant noise and disturbance, is suggested to show the effectiveness of these new types of matrix inversion.

• Abstract

A state-synchronization method for physically based simulations provides equivalent visual scenes at remote sites on ring-like networks. The simulation runs independently on each participating site so that sites can immediately process and display any local user's action, allowing high responsiveness.

• Abstract

This paper addresses a new control strategy for synchronizing two or more distributed and interconnected dynamic systems having communication time delays. The proposed strategy that uses the Smith predictor principle and delay information not only achieves synchronization but also preserves the natural local dynamics of each subsystem without being affected by the feedback nature of control. The proposed synchronization scheme is generalized to cases that deal with an arbitrary number of heterogeneous interconnected systems through dynamic scaling of input under a ring-type network configuration. In addition, possibility of applying the proposed scheme to nonlinear systems is discussed. Simulation and experimental tests are conducted to validate theoretical results.

• Abstract

In this paper, we present a grasp planning method using grasp taxonomy and object primitives. Our grasp taxonomy includes newly defined grasp methods such as thumb supported pinch and palm supported pinch, to enhance grasp robustness. On the target surface, locations of finger-print that will be contacted by the robot fingers are sampled. The sampling is made to be consistent to the grasp taxonomy, called preformed grasps, matched to the target object. We perform simulations to examine the validity and the efficacy of the proposed grasp planning method.

• Abstract

This article presents both a proposal for a linear PID composite controller, composed of slow and fast sub-controllers, for flexible link robot systems modeled using the singular perturbation approach, and an efficient tuning method for the proposed controller structure. For the slow sub-controller, a PD controller with disturbance observer is used, which eventually takes on PID form. For the fast sub-controller, modal feedback PID control is utilized. The integral action in the controller removes steady state error in the joint caused by step disturbance and imperfect gravity compensation, although it also complicates the analysis. Effects of tuning the parameters of the controller to the closed loop response are investigated, and guidelines on the performance tuning for many flexible systems thus delivered. Through simulation and experiments, the adequacy and performance of the proposed method are verified.

• Abstract

This paper introduces a position-based robust visual servoing method which is developed for operation of a human-like robot with two arms. The proposed visual servoing method utilizes SIFT algorithm for object detection and CAMSHIFT algorithm for object tracking. While the conventional CAMSHIFT has been used mainly for object tracking in a 2D image plane, we extend its usage for object tracking in 3D space, by combining the results of CAMSHIFT for two image plane of a stereo camera. This approach shows a robust and dependable result. Once the robot's task is defined based on the extracted 3D information, the robot is commanded to carry out the task. We conduct several position-based visual servoing tasks and compare performances under different conditions. The results show that the proposed visual tracking algorithm is simple but very effective for position-based visual servoing.

• Abstract

In this paper, we propose a synchronization scheme to achieve a high level of consistency in peer-to-peer-based shared virtual environments (SVEs), as well as to display natural and realistic motions of virtual objects, in collaborative haptic tasks. The synchronization scheme utilizes an advanced feedback controller to compensate for the state error between geographically separated sites with a significant amount of time delay. It is designed using the mathematical model of a two-user SVE manipulating a freely moving object represented as a mass with damping resistance, with a haptic interface. Thanks to feedback control theory of time delay systems, the controller is shown to result in closed-loop stability and is be robust to perturbations in the time delay. Together with the synchronization control, a recovery filter is also designed and integrated so as to preserve the natural behavior of the synchronized object, which is, otherwise, affected by the feedback control action. In addition to verifying the theoretical results, two experiments using real Internet and local area network communications are carried out. These tests clearly support the validity of the analyses and demonstrate the applicability of the synchronization scheme.

• Abstract

Conventional limb rehabilitation requires a person-to-person meeting in a same physical place within a fixed setting. The virtual reality (VR) aid for rehabilitation therapy eliminates such limitations by utilizing computer generated virtual environment and off-the-shelf haptic devices. In the proposed upper limb rehabilitation system, two identical VR systems, placed one in the expert (therapist) location and the other in the learner (patient), are connected via communication network, enabling interactive rehabilitation training in separate places. For the effective training and evaluation, the expert and learner’s haptic devices are synchronized in real-time with slight active correction by human’s active visual feedback. To verify the feasibility and usability, example tests are presented for the developed laboratory test system.

• Abstract

In this work a method to characterize soft tissue properties for mechanical modeling is presented. Attention is especially focused on developing a model of the lower esophagus to be used in a surgical simulation, which shows a promise as a training method for medical personnel. The viscoelastic properties of the lower esophageal junction are characterized using data from animal experiments and an inverse FE parameter estimation algorithm. Utilizing the assumptions of quasilinear- viscoelastic theory, the viscoelastic and hyperelastic material parameters are estimated to provide a physically based simulation of tissue deformations in real time. To calibrate the parameters to the experimental results, a three dimensional FE model that simulates the forces at the indenter and an optimization program that updates new parameters and runs the simulation iteratively are developed. It was possible to reduce the time and computation resources by decoupling the viscoelastic part and elastic part in a tissue model. The comparison of the simulation and the experimental behavior of pig esophagus are presented to provide validity to the tissue model using the proposed approach.

• Abstract

A robust minimum-time control (RMTC) strategy is addressed and it is extended to the dualstage servo design. Rather than conventional switching type sub-optimal controls, it is a reference following control approach where the predetermined minimum-time trajectory (MTT) is tracked by the perturbation compensator based feedback controller. First, the minimum-time trajectory for a mass-damper system is derived. Then, the perturbation compensator to achieve robust tracking performance in spite of model uncertainty and external disturbance is suggested. The RMTC is also applied to the dual-stage positioner which consists of coarse actuator and fine one. To best utilize the actuation redundancy of the dual-stage mechanism, a null-motion controller to actively regulate the relative motion between the two stages is formulated. The performance of RMTC is validated through simulation and experiment.

• Abstract

This paper aims at presenting robustness analysis under the uncertainties of the time delay and plant parameters in, symmetrically coupled dynamic systems connected through network having time delay. The delay-involved closed loop characteristic function is mathematically formulated, incorporated with active synchronization control. And the robust stability of the corresponding system is analyzed by investigating the formation of characteristic equation containing second-order terms of uncertainty variables representing delay and plant dynamics mismatches. For the two individual types of uncertainties, we elucidate details of how to compute the bounds and what they imply physically. To support the validity of the mathematical claims, numerical examples and simulations are presented.

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This article proposes a smooth path generation and time scheduling method for general tasks defined by non-smooth path segments in industrial robotic applications. This method utilizes a simple 3rd order polynomial function for smooth interpolation between non-smooth path segments, so that entire task can effectively maintain constant line speed of operation. A predictor-corrector type numerical mapping technique, which correlates time based speed profile to the smoothed path in Cartesian space, is also provided. Finally simulation results show the feasibility of the proposed algorithm.

• Abstract

A straightforward inverse kinematic algorithm for multilink flexible robots is proposed to improve the control performance. The inclusion of a dynamic constraint maximizes the performance of feedback controllers in high-speed applications. To obtain a numerically feasible solution, the singular perturbation approach is employed, which decomposes the inverse kinematics into an averaged part (slow part) and a parasitic part (fast part). The solution of the averaged part is considered the desired inverse kinematics, while the parasitic part is intentionally removed. The parameter expansion is carried out to obtain the solution sequentially. The implicit expansion method, which is a refined version of the expansion method, reduces computing time considerably. The formula in discrete time offers efficiency in computer applications. In addition, a requirement on differentiability of the desired task trajectory is derived.

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The accessibility of horizontal vibration in a 3-D two-link flexible robot shows configuration-dependent nature (International Journal of Robotics Research 16 (1997) 567). This paper deals with physical meaning of the accessibility issue in conjunction with system mode approach. The identifiability which is dual to the accessibility is also discussed. The analysis of horizontal vibration based on system mode approach takes an important role in examining the vibration accessibility. The ensuing Lagrangian dynamic formulation enables the formal definition of rigid-flexible coupled dynamic terms which show clear physical meaning. Both theoretical and numerical studies are presented to elucidate the meaning of the accessibility and the identifiability of horizontal vibration. In addition, the experimental results support the theoretical results. (C) 2003 Elsevier Ltd. All rights reserved.

• Abstract

This paper deals with the system mode analysis of horizontal vibration for 3-D two-link flexible manipulators. For the analysis, we formulate and solve a set of partial differential equations which represent vibration mixed with bending and torsional moment. The inclusion of torsional vibration complicates the analysis, but the results are more precise and realistic. We obtain a number of geometrical and dynamical boundary conditions depending on manipulator configuration. There are two possible boundary conditions at the rotary joint: clamped and pinned with spring condition. We perform a examination and comparison between the two joint conditions. Numerical and experimental tests show the validity and effectiveness of the proposed analysis and modelling. (C) 2003 Elsevier Science Ltd. All rights reserved.

• Abstract

For joint tracking control of flexible robots, this paper presents a two-step design of controller: the bandwidth modulation with modal,feedback approach, First, We focus on the design of rigid parts motion controller considering the bandwidth of the rigid sub-system. Vie investigate the relationship between macro joint tracking performance and vibration suppression capability using the bandwidth parameter Alter adjusting the band-width of rigid motion. the composite control, which is the second step Consisting of rigid and flexible sub-controllers. is applied like singular perturbation approach. As the flexible sub-controller, we propose a direct modal feedback controller that is very simple, but effective to suppress the vibration. The validity and effectiveness of the proposed method are are verified by experiments using a POSTECH 3-D flexible robot.

• Abstract

An improved composite controller of singular perturbation approach is designed for controlling a multi-link flexible robot with uncertainties. We adopt the standard form of a singular perturbation approach for modeling. To reduce the coupling effect from flexibility, the bandwidth of a slow subsystem is modulated by considering the fundamental frequency. The disturbance observer provides a means for defining the bandwidth of a slow subsystem as well as compensating disturbances. At the same time, uncertainties in the fast subsystem are updated to enhance the capability for vibration suppression in conjunction with PID (Proportional-integrative derivative) modal feedback. We draw conditions for Lyapunov stability of the modal feedback and adaptive scheme. A numerical simulation will support the validity of our research results. (C) 2002 Wiley Periodicals, Inc.