Elephants cannot intentionally control individual trunk muscles but instead generate coordinated movements. This coordination, known as kinematic synergy, allows muscles to work together, reducing the controlled degrees of freedom (DOF) while enhancing motion efficiency. In this paper, we develop an elephant trunk robot that generates coordinated motions with only a few actuators inspired by kinematic synergy. First, we analyze elephant trunk motion using video data and extract the principal components that closely approximate actual movements. Next, we design a robot based on an underactuated tendon-driven transmission to reproduce the selected principal components and a control system to reduce tracking errors. Especially, we focus on designing tendons to confine the motion within the space spanned by the principal components. Finally, we implement the control system and evaluate the robot’s performance in replicating trunk motion with a limited number of actuators. By generating coordinated motion, we showed the effectiveness of the transmission system design method and the improvement in the motion accuracy by the control system.

Recently, it has become possible to easily design and fabricate robotic systems in the laboratory and at home due to the recent development of 3D printer technology. On the other hand, the strength of the plastic materials used in reasonably priced 3D printers and the accuracy of the printed parts are generally low. These problems affect the part-joining quality. Therefore, this paper describes a design method inspired by ancient Japanese wooden joinery techniques for assembling 3D-printed parts and presents the design of a robotic hand as its application. The joinery techniques use special shapes to assemble components and allow us to assemble the robotic hand without glue, screws or nails and to easily disassemble it.

Synergy provides a practical approach for expressing various postures of a multi-fingered hand. However, a conventional synergy defined for reproducing grasping postures cannot perform in-hand manipulation, e.g., tasks that involve simultaneously grasping and manipulating an object. Locking the position of particular fingers of a multi-fingered hand is essential for in-hand manipulation tasks either to hold an object or to fix unnecessary fingers. When using conventional synergy based control to manipulate an object, which requires locking some fingers, the coordination of joints is heavily restricted, decreasing the dexterity of the hand. We propose a functionally divided manipulation synergy (FDMS) method, which provides a synergy-based control to achieves both dimensionality reduction and in-hand manipulation. In FDMS, first, we define the function of each finger of the hand as either "manipulation" or "fixed." Then, we apply synergy control only to the fingers having the manipulation function, so that dexterous manipulations can be realized with a few control inputs. Furthermore, we propose the Synergy Switching Framework as a method for applying a finely defined FDMS to sequential task changes. The effectiveness of our method is experimentally verified.

This paper presents a force-sensorless collision detection approach based on virtual contacts. A series of indices based on virtual instantaneous powers are introduced associating to several virtual contacts defined on corresponding links of a manipulator. A possible contact link can be determined by comparing the introduced indices without any force or tactile sensors. Simulation results of 2D collision detection tasks by using a three DOF (Degree of Freedom) planar manipulator and 3D collision detection tasks by using a six DOF spatial manipulator validate the effectiveness of the proposed collision detection approach.

This paper proposes a method to design low-cost robotic hands that require almost toolless assembly, and have special transmissions and joint mechanisms. The transmissions consist of active and passive gear trains manufactured by 3D printers to realize coordinated motions among joints and to transmit the driving force to underactuated joints. The joints are designed with pop-in structures to simplify the assembly of the designed robotic hands and its maintenance. The robotic hands even enabled us to exchange some components without necessitating a shutdown. By using these techniques, we manufactured two robotic hands with different passive gear trains. One of the hands had three fingers with stiff constrained gear trains and soft fingertips, and the other had five fingers with elastic gear trains. Experiments were conducted to validate the performance of the proposed robotic hands and to clarify the roles of the different gear trains.

This paper proposes a design method of transmissions for underactuated mechanisms. This transmission consists of active and passive gear trains that align a series of gears over several joints. The transmission has no kinematic singular point that restricts the workspace. Thus, arbitrary joint-connected motions of the underactuated mechanisms can be designed by combining the gear trains. We investigate the kinematics and statics of underactuated mechanisms to find a transmission matrix that realizes the desired connected motions and adaptive grasps. We also develop a method to design gear trains that corresponds to the transmission matrix. We extend this design method with stepped gears and belt-gear mechanisms to increase the design flexibility. The proposed method was experimentally validated using the two- and three-jointed mechanisms.

Tendon-driven mechanisms (TDMs) are mechanisms driven by more tendons than joints. This tendon redundancy is often used for changing the hardware compliance. In contrast, in this paper, the redundancy is used for coping with unexpected tendon breaking. We analyze kinematics of a class of TDMs with asymmetrically spanned tendons and modify it to design a TDM that preserves the controllability even if at least one of the tendons is broken. We validate the proposed method to design several TDMs.

This paper designs a new five-fingered robotic hand with a camera. Several morphological features of the human hand are integrated to improve the appearance of the hand. The drive system of this hand is under-actuated to eliminate the weight of the hand and to embed all the actuators inside the palm. Despite of this under-actuation, this hand can grasp objects in several different ways. In addition, the two different transmissions are adopted to drive the fingers according to their roles. These transmissions help not only to improve drive efficiency but also to secure the space of the embedded camera.

This paper designs a new underactuated robotic finger using a special transmission mechanism. The transmission mechanism consists of a set of gears and a spring to produce connected motions and adaptive curling when the finger moves in free space and when it contacts with the environment, respectively. The connected motion is realized by kinematic constraints of the joints instead of the static equilibrium of joint elastic elements that are frequently adopted in underactuated mechanisms. The motor torque is effectively used to increase the gripping force due to the mechanism. In addition, a reduction of the transmission components also simplifies the assembly process and decreases the size and weight of the finger, which is useful in attaching it to the arm as a prosthesis.

This paper analyzes tendon-driven mechanisms (TDMs) with active and passive tendons and proposes a method for designing TDMs. First, we group TDMs into six classes according to their controllability and the number of driving degrees of freedom. In this classification system, the conventional underactuated mechanisms are grouped into three classes, two of which have often previously been grouped together although they have different manipulation abilities. Next, we analyze bias forces to separate and decouple a given TDM into several smaller TDMs. Finally, we propose a design method for combining smaller TDMs into an appropriate TDM. Using this method, we can easily determine an appropriate tendon transmission that meets the requirements for the number of tendons, the hardware of the tendon routing, and arbitrary joint constraint that has useful applications in prosthetic and biomimetic hands. Numerical examples show that the proposed method guarantees a nonsingular series actuation transmission and that the designed underactuated TDMs could achieve arbitrary stiffness independent of the actuation effort compared with the conventional underactuated TDM with torsion springs.

In this paper, an under-actuated robotic hand is designed for realizing several different grasps. Three special transmissions are developed to realize the compact joint connected motion, connected motion among fingers and adduction/abduction. These transmissions reduce the volume and weight of the hand while maintain functions necessary for realizing desired grasps. The developed robotic hand can choose three different opposed positions of the thumb to realize four different grasps. Experiments are conducted to confirm that the robotic hand moves fast and stably grasp objects.

This paper proposes a joint control method for tendon-driven mechanisms (TDMs) with branching tendons, in which multiple tendons are connected at a point, and which are often found in musculoskeletal systems. TDMs usually require the same number of tendons as actuators, which are one of the heaviest components in a robotic system. The utilization of branching tendons is useful for reducing the number of actuators needed when making lightweight robotic mechanisms, such as prosthetic hands. However, the under-actuation of branching tendons makes it difficult to accurately control the joint motion of TDMs. Therefore, TDMs with branching tendons have been used only for simple adaptive grasping mechanisms. In this paper, we derive the tendon kinematics of TDMs with branching tendons and design a joint PD controller for the mechanisms. We demonstrate the stability of the control system using Lyapunov's direct method. We show that the bias force setting, which does not appear in conventional TDMs, is important in the realization of accurate control in TDMs with branching tendons. Simulations were performed to evaluate the proposed method.

This paper describes a supervisory control system for a multi-fingered robotic hand. The proposed method enables a slave robotic hand to grasp an object in a remote environment in several ways, manipulate it, and mimic several non-grasping motions. The key components of the proposed control system are a grasping selector in the master system and motion controllers and a controller selector in the slave system. The grasping selector learns to detect motions commanded by an operator using datagloves. We developed two methods to learn the operator's hand shapes, one that prioritizes the learning time and one that prioritizes the probability of correct detection. The controller selector determines the current command and awaits a transition, while the motion controllers stably realize the currently commanded motion. We have demonstrated the stable operation of a three-fingered robotic hand using the proposed method.

Estimation of joint torque is an important objective in the analyses of human motion. In particular, many applications seek to discern torque during a desired human motion, which is equivalent to solving the inverse dynamics. The computed torque method is a conventional means of calculating inverse dynamics. The obtained torque, however, invariably includes errors resulting from inexact inertial and viscoelastic parameters. This paper presents a method for solving the inverse dynamics of a human arm passively during tracking. To achieve precise human motion tracking, iterative learning control is used for motion generation. Some experiments that target a human arm are executed to validate the proposed method.

This paper presents an image-based visual servoing for controlling the position and orientation of a quadrotor using a fixed downward camera observing landmarks on the level ground. In the proposed method, the negative feedback to the image moments is used to control the vertical motion and rotation around the roll axis. On the other hand, the negative feedback cannot be used to control the horizontal motion due to under-actuation of a quadrotor. Thus, a novel control method is introduced to control the horizontal motion. Simulations are presented to validate the proposed method.

This paper proposes a balance control method for a biped based on passivity. In this method, we design a controller to stabilize the position of the center of mass (COM), the orientation of the upper body and the motion of the swing leg using the kinematic model of a biped. The proposed method is not hindered by complexity of the computation because the proposed controller executes no contact force planning, and uses only a compact feedback for implementation. It is also robust to errors caused by the environment or internal motion. We prove the stability of the system according to the Lyapunov's direct method. Selected simulations are executed to validate the effectiveness and robustness of the proposed controller.

This paper introduces a control method for a powered planar biped without ankle actuation. The existence of an ideal slope, on which the biped can walk without actuation, is assumed. The proposed controller can realize stable walking, as if the biped were on an ideal slope when the biped is on a different slope. The proposed controller has no singular points, whereas the control input diverges to infinity, unlike conventional controllers for powered passive walkers. Selected simulations were executed with a simple compass-like biped and a four-link biped with a mass body to validate the effectiveness of the proposed controller.

Many robotic hands or prosthetic hands have been developed in the last several decades, and many use tendon-driven mechanisms for their transmissions. Robotic hands are now built with underactuated mechanisms, which have fewer actuators than degrees of freedom, to reduce mechanical complexity or to realize a biomimetic motion such as flexion of an index finger. The design is heuristic and it is useful to develop design methods for the underactuated mechanisms. This paper classifies mechanisms driven by tendons into three classes, and proposes a design method for them. The two classes are related to underactuated tendon-driven mechanisms, and these have been used without distinction so far. An index finger robot, which has four active tendons and two passive tendons, is developed and controlled with the proposed method.

The purpose of this paper is to describe the construction of a supervisory control system for telemanipulation of a robotic hand with a Data Glove. This system aims to establish interaction control such as preshaping, grasping, and orienting operations. The system consists of a Data Glove as a master device, as well as slave controllers and a slave robot. The feedback loop of the slave system is closed at the slave side so that the slave controllers manipulate an object stably following commands from a Data Glove. A Data Glove usually extracts a subject's hand shape in order to map it to a slave hand. However, the proposed method only extracts a few key pieces of information which slave controllers require. We explain the proposed system and propose a way to extract the key information with a Data Glove. An experiment is executed to validate the proposed method.

To date, many control algorithms have been proposed for grasping of rigid objects, through fixed or rolling contact in a horizontal plane, by multi-fingered robotic hands. However, these non-sliding contacts have not been considered in a single model. Here, by examining kinematics, we present a single model for both fixed and rolling contacts in a horizontal plane, and show that a fixed point contact is a special case of a rolling contact. We introduce a blind grasping algorithm with tactile feedback, and show that the algorithm does not require any tactile feedback in the case of a fixed point contact. Numerical simulations show that the algorithm is applicable for stable pinching with non-sliding contact

This paper proposes a novel control method for enabling a robotic arm with a pair of two degrees of freedom (DOFs) robotic fingers as an endeffector to execute a variety of superimposed tasks in a coordinated way. Differently from conventional control methods previously proposed for arm-hand systems that adopt a separate design to control each robotic part, such as an arm and a hand, the proposed method designs a unified single control scheme for movements of the whole robotic arm-fingers system. It is assumed that finger-tips are rigid and there are rolling constraints between the finger-tips and a target object, and whole motion of the system is confined to the horizontal plane. The results of numerical computer simulation demonstrate that the proposed method is sufficiently effective in control of such a whole robotic arm-fingers system, and in particular is applicable to superimposed tasks, grasping, regulating, and replacing a target object through composition of the control signal based on the principal of superposition. It is concluded that special attentions in design of control signals should be paid to the wrist that combines the finger parts to the arm

In this paper we propose a control method for pinching an arbitrary shaped object in a horizontal plane by a multi-fingered robot with arbitrary shaped fingertips. It is assumed that the constraints between the fingertips and the object is rolling and smooth, and each finger contacts with the object at one point. The controller requires no object information, no preplanning and no force sensors. It uses only joint angle, joint angular velocity, contact points (tactile feedback) and the fingers' link length. The paper begins with an derivation of dynamics of the finger-object system. We propose a stable grasping controller and briefly show the proof of dynamic stability of the system. The simulation results demonstrate that the controller with tactile feedback can easily realize the stable pinching

In this paper, we study co-activation of digitorum muscles while perform stable pinching and posture regulation tasks of an object by using dual fingers. The fingers have 2 D.O.F. joints and are actuated by nonlinear redundant digitorum muscles to mimic human-like pinching movements. Firstly, we illustrate the kinematics and the dynamics of the overall system, which consider not only the fingers and an object, but also three muscles for each finger to actuate the finger links. Secondly, we consider nonlinear muscle property based on several physiological studies, and propose sensory-motor control rule to the muscles in order to realize stable pinching simultaneously with posture regulation by introducing internal force term induced by co-activation between flexor digitorums and extensor digitorums to modulate the damping factor in joint space. We verify our study by numerical simulations and conclude that this dual fingers system can realize human-like stable pinching and posture regulation

This paper aims to formulate a dynamic model of a pair of dual multi-DOF robotic fingers with rigid tips grasping a circular-shaped object and proposes a new control framework for dexterous manipulation. Firstly, based on the Lagrange method and Hamilton's principle, a dynamic model of the general object-fingers setup has been described as a system of algebraic differential equations composed of ordinary differential equations governing dynamics of the fingers and the object and a set of algebraic constraints governing rigid contacts between two finger-tips and object' surfaces. Secondly, a control algorithm for stable grasping of the object by the pair of fingers has been proposed. Thirdly, another control signal for desired orientation and position of the grasped object has been proposed and asymptotic convergence of the closed dynamics to the desired orientation and position has been analysed. The principle of linear superposition of control signals has been applied to ensure stale grasping while control desired motion. Numerical simulation results have reconfirmed the effectiveness of the proposed control law.

The purpose of this paper is to construct a supervisory control system for telemanipulation with a robotic hand and to introduce some basic strategies of the systems and a case study, in which a robotic hand in a remote side does preshaping, grasping and orienting. The developed master system is designed based on human pinching motion and can be manipulated intuitively. The feedback loop of the developed slave system is closed at the slave side and the slave robotic hand can manipulate an object reliably. Three experiments are executed to confirm that the slave hand pinches objects and controls their orientation angle easily even time delay exists

This paper presents a new ankle-foot orthosis (AFO) for hemiplegic patients. The proposed AFO has a pneumatic passive element with a rotation axis at the ankle joint. The ankle-joint constraint force can be adjusted according to the subject's gait phase. We confirmed that adjusting of the pneumatic pressure in the proposed pneumatic passive element enables the device to duplicate the performance of many conventional AFOs

This paper is aiming at showing a sensory-motor coordination control scheme that realizes stable pinching of rigid objects with parallel or non-parallel flat surfaces movable in 2-dimensional vertical plane by a pair of robot fingers with hemispherical ends. The proposed control signal is composed of gravity compensation for fingers, damping shaping, exertion of forces to the object from opposite directions, generation of moments for rotational moment balancing, and regressors for estimating unknown steady-state terms, all of which neither need the knowledge of object parameters nor use any object sensing data. In other words, stable grasping can be realized by using only finger joint sensing in a blind manner without using force sensors and tactile sensing. Stability of pinching motion with convergence to the state of force/torque balance is shown through computer simulations and is also proved theoretically.

This paper explores what are the fundamentals of physiologically inspired robot control through investigating two interesting but difficult problems of robot control: 1) robotic hand-writing and 2) human-like multi-joints reaching with surplus DOFs (Degrees-of-Freedom). Noteworthy characteristics in control of these systems are a) redundancy in DOF, b) dexterity in execution of a target task, and c) indispensability of sensory motor coordination, though d) their dynamics are nonlinear and governed by geometric constraints in the former system. Due to these inherent characteristics, both the conventional control-theoretic approaches originated from the linear system theory and Lyapunov’s direct method are likely to fail. By gaining physical insights into these nonlinear dynamics with redundancy in DOFs and physical descriptions of target tasks, this article claims that a symbiosis of “robotics” and “neuro-physiology” is quite effective in finding a simpler sensory-motor coordination principle in each case that leads to accomplishment of each imposed task regardless of annoying characteristics of its motion dynamics with nonlinearity and DOF-redundancy.

The human thumb is a digit playing crucial roles among all digits used for object manipulation. The special feature of the thumb termed as pad-opposition with four other fingers makes human precision manipulation possible, and during four other fingers dexterously manipulate an object, the thumb functions as a role of stably supporting other's manipulating motions within the pad-opposition. In various characteristics of the thumb, this paper concentrates upon the large radius of pad curvature of the thumb compared with those of four other fingers. In order to show the influence of the large pad curvature, it is shown that reiterated fingering motions can be easily generated by a pair of robotic fingers with different pad curvatures by using a sensory-feedback. It is also shown from computer simulations and experiments that the pad curvature automatically distinguishes roles of the thumb and other fingers. It is finally claimed that the thumb plays a crucial role in enhancement of dexterity and stability in such an implicit manner that it helps the other opposite finger with less pad curvature to make a swift rolling movement that can sophisticatedly control movements of the object.

This paper proposes a manipulation of a circular object in a horizontal plane by a pair of finger robots. This method guarantees the dynamic stability of the system and does not require any object models and object sensing to manipulate the object. It is assumed that there is no friction between the object and the horizontal plane and it is possible to be adequately large friction between the fingertips and the object. We examine the condition of stable grasping of a circular object and propose controllers for stable grasping and for controlling its approximate relative orientation angle without object sensing. The experimental results show the validity of the controller.

This paper proposes a method for controlling an object with parallel surfaces in a horizontal plane by a pair of finger robots. The control method can achieve stable grasping, relative orientation control, and relative position control of the grasped object. The control inputs require neither any object parameters nor any object sensing, such as tactile sensors, force sensors, or visual sensors. The control inputs are also quite simple and do not need to solve either inverse kinematics or inverse dynamics. The stability of the closed-loop system is proved, and simulation and experimental results validate the control method.

In order to enhance dexterity in execution of robot tasks, a redundant number of degrees-of-freedom (DOF) is adopted for design of robotic mechanisms like robot arms and multi-fingered robot hands. However, it is said that surplus DOF of such a robotic mechanism incurs a problem of illposedness of inverse kinematics from task space to joint space. This paper attempts to show that, in the case of a pinching task (grasping in 2D space), by using a pair of robot fingers with hemispherical finger ends, 1) the ill-posedness of inverse kinematics can be resolved in a natural and dynamic way by means of sensory feedback signals from task space to joint space and 2) surplus DOF of fingers enhances dexterity of pinching tasks by remarkably accelerating the speed of convergence toward target object manipulation.

This paper proposes stable grasping and angle control methods of an object with parallel surfaces by a pair of finger robots in a horizontal plane. The method does not require any object sensing for stable grasping but only measurement of the object angle for absolute orientation angle control. Relative orientation angle control of the grasped object can be attained even if no object sensing is used.

In order to enhance dexterity of a robot hand, it is said that the robot should be designed to have a redundant number of degrees-of-freedom(D.O.F.). However, in redundant robotic systems, the inverse kinematics from task-description space to joint space becomes ill-posed. Therefore the problem of determination of joint motions becomes difficult. In order to avoid this ill-posedness, many methods have been proposed, most of which introduce an additional input term calculated from minimization of some intentionally introduced artificial index of performance. This paper treats a 4-D.O.F. redundant handwriting robot by using a novel and simple control method and resolving the problem of such ill-posedness based on sensory feedback in task-coordinates. The effectiveness of the proposed control method is demonstrated through computer simulation and a preliminary experiment.

This paper is aiming at clarifying the relationship between the total DOF (degree-of-freedom) of a pair of robot fingers and feasibility of concurrent control of stable grasping and object manipulation of a rigid object with non-parallel surfaces under the gravity effect. It is shown by computer simulation and an actual experiment that if each finger has at least two DOF then the desired task of concurrent stable grasping and posture control can be attained, though the use of a pair of dual fingers with three DOF is shown theoretically to be feasible. It is also shown that the use of fingers with single DOF and two DOF cannot be feasible under the gravity effect, though it is feasible in the case that the gravity effect can be ignored.

The purpose of this paper is to propose a new impedance control concept for elastic joint robots with programmable passive impedance devices in the transmission. The concept allows us to use the same index both for free motion and for contact task. We apply it to a one-DOF elastic joint robot and derive an adjustment law for the robot. The numerical simulations show that implementation of the concept can be realized without any dynamic models.