Hand motion tracking is essential in many fields, e.g., immersive virtual reality, teleoperation of robotic hand, and hand rehabilitation of stroke patient, as human hand plays a crucial role in our daily life. The highly under-actuated hand exoskeleton, which can track the 6-DoF motions of each fingertip via a highly under-actuated kinematic chain, exhibits many benefits in wearability and portability over other solutions. However, due to the non-anthropomorphic linkage, this hand exoskeleton also encounters difficulties in measuring human-finger’s joint angles. While the joint-space is important in many scenarios, such as teleoperating a robotic hand with anthropomorphic kinematics but with different size to human. Here we proposed a new method to reconstruct the human finger joints by using a highly under-actuated hand exoskeleton. Our key contribution is the arc-fitting algorithm, which is able to calibrate the misalignment between the exoskeleton’s and the human-finger’s base frames and estimate the length of human’s phalanxes, by using the fingertip’s circular motions. With knowing the aforementioned informations, the joint angles can be reconstructed in high precision based on the inverse kinematics models of human fingers. Furthermore, our proposed method is compared with a baseline method, in which the joint angles obtained by a motion capture system are served as ground-truth. The results demonstrate that our proposed method exhibits excellent performance in reconstructing finger’s joint configurations.

The Incomplete Orientation Constraint (IOC), which does not require a controlled motion constrained by all three spatial directions, exists widely in a lot of robotic tasks. However, the IOC remains a challenge for existing methods, due to the nonlinear structure of the rotation group SO(3). Moreover, the IOCs are time varying in the trajectory tracking problem, which makes it more challenging than the set-point control. To address the IOC problems, we define, identify and prove the closed-form solution of the perpendicular curve in SO(3). Based on the proposed perpendicular curve, we develop a new trajectory tracking controller considering the IOC. Compared with existing methods, the proposed method can achieve faster and more accurate tracking results. Moreover, the proposed method can be applied not only to manipulators with redundancy (including both functional and intrinsic redundancy), but also to manipulators that are non-redundant. Furthermore, it is easier to incorporate a secondary optimization objective into consideration for the intrinsic redundant case, which is difficult for existing methods. The proposed method has been implemented on both simulations and experiments. The numerous simulation and experimental results validate the effectiveness and advantages of the proposed method. Note to Practitioners—The trajectory tracking control with IOC is important and can be applied in a wide spectrum of robotic-assisted manufacturing, e.g. arc-welding, engraving, etc.. In this paper, a perpendicular curve-based trajectory tracking method is proposed to consider the IOC automatically. It is no longer necessary to carefully plan a reachable orientation trajectory. Users only need to focus the planning of the tool direction, which is determined by the tasks. In addition, the proposed method can achieve faster and more accurate tracking result. Moreover, it is universal and can be applied to both redundant and non-redundant cases.

Orientability is an important performance index to evaluate the dexterity of haptic master devices. Currently, most of the existing haptic master devices have limited workspace and limited dexterity. In this paper, we present the RemoT-ARM, a 6 Degree-of-Freedom (DOF) haptic master device that can provide larger and more dexterous workspace for operators. To evaluate its reachability of orientations, we propose a novel orientability index. Furthermore, a relative orientability index is proposed to characterize the matching degree of the workspace of a given manipulator to its target workspace. The volume, the manipulability and the condition number are also introduced as performance indices to evaluate the size and the isotropy of the workspace. According to these performance indices, all possible configurations for the RemoT-ARM have been taken into consideration, analyzed, and compared to finalize its optimal configuration.

This work presents a novel method for estimating online the torques at the ankle, knee and hip of a user with the goal of generating reference signals for torque controlled lower limb exoskeletons. In particular, this approach attempts to address difficulties arising in real life scenarios when noncyclic locomotion activity, unexpected terrain or unpredicted interactions with the surroundings occur. An advantage of the proposed method is that it does not require any information on the user's upper body (i.e. pose, weight and center of mass location)or on any interaction of the user's upper body with the environment (i.e. payload handling or pushing and pulling task). By monitoring the interaction of the user's feet with the ground through a novel sensorized shoe sensing system, the method applies an inverse static analysis on the user's lower limbs to estimate in real time the torque at each leg joint. The system is fully wearable, ergonomic and portable and uses a reduced number of body posture sensors. The design of the sensorized shoes permits plantar flexion, while measuring the toe and heel orientation and the interaction loads. This allows walking on irregular terrains and natural feet postures in different tasks. Trials were performed to validate the proposed approach under different tasks and terrains. Finally, the knee torques estimated online by the proposed strategy were used as reference signals to drive the iT-Knee Bipedal System in an assistive task.

In this work a novel synergy-based bilateral tele-manipulation strategy is introduced. The proposed algorithm has been primarily developed to remotely control the Pisa/IIT SoftHand (SH) using a 3-finger hand exoskeleton as master device. With a single actuator and a sensory system limited to a position encoder and a current sensor, the SH minimalist design promotes robustness but challenges traditional teleoperation strategies. To tackle this challenge, the concept of Cartesian-based hand synergies is introduced as a projection tool which maps the fingertip Cartesian space to the directions oriented along the grasp principal components. The unconstrained motion of the operator's hand is projected on this space to extract the SH's motor position reference. Conversely, the interaction force estimated at the robotic hand as a 1-dimensional force along the first synergy is projected to the 9D fingertip Cartesian space through an inverse projection. The resultant finger-individualized forces form a synergy based weighted representation of the grasping effort applied by the SH and are displayed to the operators fingertips using the force feedback hand exoskeleton. The system's ability to reflect the environment's impedance has been experimentally validated during a ball squeezing experiment. To assess the overall effectiveness of the proposed system as a manipulation interface, the SoftHand was mounted on the humanoid robot COMAN and the setup was subsequently enriched with a vision-based tracking system monitoring the operators wrist trajectory. Experimental results indicate that the proposed body-machine bilateral interface allows for the intuitive performance of stable grasps and transport of a large range of diversely shaped objects.

This work presents the development of iT-Knee, a novel modular knee exoskeleton that makes use of a torque transmission interface to deliver pure assistive torque to the knee articulation, with the objective to act as rehabilitation tool, or a single joint add-on exoskeleton device for power augmentation. The specific kinematics features employed by iT-Knee can accommodate not only the translational of the knee instantaneous center of rotation in the sagittal plane and on its orthogonal direction, but also the knee varus/valgus angle as well as the internal/external rotation tibia movements delivering pure torque only around the flexion/extension movement. This functionality results in superior transparency and comfortability which allow prolonged period of use without generating significant discomfort. The iT-Knee kinematics, its mechanism, implementation, and actuation are introduced. The Self-aligning feature combined with a fast lock/release mounting system on the human leg shortens the setup time required to wear it, increasing its user-friendly perception. iT-Knee uses a torque controlled actuation unit to generate torque around the knee flexion extension enabling the implementation of several interaction control schemes that combine assistive functionality on demand with high back drivability and transparency during unloaded free motions of the human knee. Experimental results are presented and effectively demonstrate the functionality of the iT-Knee device.

Exoskeletons offer an intuitive method for actuating multiple DOF of the body; this makes them attractive for applications where generation and coupling of artificial forces to the limbs is needed. Force feedback hand exoskeletons have been continuously considered for whole hand haptic interaction in virtual reality simulators, in teleoperation setups and for rehabilitation. In hand exoskeletons finger tracking, actuation and transmission systems must be embedded in confined spaces, matching at the same time the profound dexterity of the hand transparently and without causing a burden. Most of the design approaches for such systems have remained largely experimental due to hardware limitations, impacting heavily on important functional and ergonomic factors. This paper presents the design of a novel 3-digit hand exoskeleton, which addresses the issues of finger tracking and force feedback. It proposes a new approach for the application of the feedback force with a single attachment at the fingertip through a 6DoF kinematic chain. This kinematic linkage allows for unconstrained reach of the fingers within their full workspace and facilitates a sensor system for high resolution 6DOF tracking of the fingertips. At the same time the highly under-actuated mechanism permits application of a bidirectional feedback force at the fingertips. The hand exoskeleton fits an large range of hand sizes and requires no mechanical alignment between the linkage and the fingers, whatsoever. Preliminary results show the efficacy of this system as a tracking and force feedback device for the hand.

This paper presents a novel hybrid actuator with controllable mechanical damping. It has been developed to provide subsequently the actuation means for haptic interfaces that can demonstrate intrinsic passive performance when rendering hard contacts. The overall actuator is a dual actuation system where one actuator is responsible for generating the joint motion while the second is dedicated to regulating the physical damping through a semi-active friction mechanism. This semi active friction mechanism applies a purely dissipative torque on the joint, which can be continuously controlled to render damping levels ranging from completely free to heavily damped and even a completely locked joint. The present work focuses mainly on the mechatronic details of the actuator design and in particular on the modelling and control of the damper. The proposed variable damping mechanism is evaluated in a simple 1-DOF joint. Experimental results are presented to demonstrate that the unit is capable of replicating physical damping with adequate performance.

In this paper we report on the development of a modular multi-DoF F/T sensor and its use in the implementation of a sensorized object capable of multi-touch detection. The sensor is composed of six 6-axis F/T sensors spatially organized on the faces of a cube. Different calibration methods are presented to directly tackle the coupling phenomena inherent to the spatial organization of the faces and the lightweight construction of the sensor which would have, otherwise, degraded its accuracy. To assess the performances of the calibration methods, a comparison is reported with respect to the measurements obtained with a commercial force/torque sensor considered as ground truth (ATI Delta). Thanks to the modular design and the possibility to cover the sensitive faces with surface patches of different geometry, a variety of sensorized objects with different shapes can be realized. The peculiar feature that all the components of the contact wrench can be measured on each face with high accuracy, renders it a unique tool in the study of grasp force distribution in humans, with envisioned use both in neuroscience investigations and robotic applications.

Haptic feedback should integrate kinaesthetic and tactile feedback. However current haptic displays do not satisfy the stringent performance and design requirements for integration in teleoperation and VR. This work presents the development of a compact, high performance tactile display for the fingertip. The compact design, high performance, reliability, and simple connectivity of this display make it suitable for immediate integration in current VR and master-slave haptic systems. In terms of performance this display achieves an excellent combination of force, amplitude and spatiotemporal resolution at the tactors, surpassing the performance of devices of a similar footprint. Its operation is based on the display of surface shape to an area of the fingertip through a 4×4 array of vertically moving tactors. The tactors are spring loaded and are actuated remotely by dc motors through a flexible tendon transmission. This work presents the overall design, control and performance of the device. A preliminary analysis of the transmission system is presented and is used to compensate for output errors induced by component elasticity.

Tactile feedback is a key modality in object exploration and manipulation. However it has not been satisfactorily addressed in master-slave teleoperation. One of the reasons is that current tactile displays do not satisfy the stringent performance and design requirements for integration in master haptic devices. This paper presents the integration of a compact, high performance tactile display in a teleoperation setup. In this scenario the tactile display provides tactile feedback while remote objects are being contacted through a soft robotic finger. The display is mounted on a force feedback master device, which controls a manipulator equipped with a force sensor and a soft finger. Force feedback and tactile feedback are combined in a hybrid approach. Force feedback on the master reflects the measured remote interaction forces while tactile feedback is model based. This hybrid feedback method can provide force and tactile information in cases of highly structured teleoperation scenes where tactile sensing is absent or rudimentary while accurate environment models exist. An experiment is presented where users teleoperated the robot finger in a 3D contour following task with and without tactile feedback. Subjects' performances indicate an improvement in teleoperation when both tactile and force feedback are present.

Interfaces capable of providing tactile and force feedback are required to enhance interaction in VR applications, especially in those applications that involve the exploration of small geometric features and manipulation of small objects. This paper presents a high performance haptic interface capable of displaying tactile and force feedback information when interacting with virtual objects. The main objective of this work is to examine the capabilities of this interface to provide realistic sensations during the exploration of small surface features, such as ridges and convex shapes. To achieve this goal, two exploratory experiments under different feedback modalities were conducted. In the first experiment was evaluated the performance of users in detecting and localizing small convex shapes. In the second experiment was measured the users' ability to discriminate the angle of two chevron-shaped ridges. Results from the first experiment indicated a significant increase in performance not only when the interface provided tactile and force feedback but also when it provided only tactile feedback. Results from the second experiment showed that relatively small differences in angle (±7%) can be discriminated using the tactile and force feedback interface. An average threshold of 6.4° was obtained.

This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned surfaces through a tactile display. The tactile display is an array of 4×4 vertically moving pins which can simulate the shape of small scale features. Its small size and low mass allow users to explore virtual surfaces freely and intuitively. The evaluation method consisted of measuring the orientation discrimination threshold for virtual surfaces with sinusoidal profiles. The threshold was compared with the threshold obtained using a non-actuated tactile display of equal spatial resolution and with the threshold obtained using the bare finger to explore real surfaces. This comparison was done to evaluate the quality of the rendered virtual surfaces, the performance of the device as a control system and the efficiency of the tactile rendering algorithm. This study also measured the speed and normal force during the tactile exploration that allowed investigation of the exploration strategies used when touching through normal indentation displays and through the bare finger. Furthermore they are the necessary interaction parameters for assessing the bandwidth and force output of the device.

The development of successful tactile displays can be assisted by the capacity to assess their performance in integrated virtual reality applications. The design of single tactor or desktop tactile displays has been useful for scientific analysis of the mechanisms of touch. Nevertheless, it does not provide useful information about the quality of immersion in VR environments integrated with tactile feedback where user mobility and comfort are paramount. The present work introduces a new wireless portable tactile display for the finger. This new device demonstrates excellent levels of force output combined with good bandwidth in a configuration of a wearable 4times4 array of vertically moving tactors. The focus of this design is small size, comfort, mobility and ultimately integration into a complete Virtual Reality system for tactile surface texture exploration with 6DOF in the finger's work envelope

Hand therapy is a major sector of physiotherapy and one of great importance. The impairment of the hand and generally of the upper limbs can be the cause of social and financial hardship and a serious cause of physical and emotional deterioration. Major efforts are directed into developing therapy methods and procedures in order to standardise and therefore successfully apply treatment regimes in a wide scale. Although, the lack of scientific measurements of statistical value that the current methods suffer due to the mostly empirical nature of examination, assessment and treatment does not assist this endeavour. This paper presents an exoskeleton based system for the physical and occupational therapy of the hand in an interactive VR environment. This system enhances the existing therapy methods with the introduction of accurate and repeatable finger motion and force measurement, interactivity, potential for great exercise assortment and statistical registration and evaluation.