Stretchable sensors indicate promising prospects for soft robotics, medical devices, and human-machine interactions due to the high compliance of soft materials. Discrete sensing strategies, including sensor arrays and distributed sensors, are broadly involved in tactile sensors across versatile applications. However, it remains a challenge to achieve high spatial resolution with self-decoupled capacity and insensitivity to other off-axis stimuli for stretchable tactile sensors. Herein, we develop a stretchable tactile sensor based on the proposed continuous spectral-filtering principle, allowing superhigh resolution for applied stimuli. This proposed sensor enables a high-linear spatial response (R2> 0.996) even during stretching and bending, and high continuous spatial (7 μm) and force (5 mN) resolutions with design scalability and interaction robustness to survive piercing and cutting. We further demonstrate the sensors' performance by integrating them into a planar parallel mechanism for precise trajectory tracking (rotational resolution: 0.02°) in real time.

With the vast demand in marine development, robotic fish show promising potential in underwater exploration for their high-performance propulsion ability. However, fish-inspired robots are yet to utilize the structural flexibility of rhythmic actuation such as bony fish (Osteichthyes). The Body and Caudal Fin (BCF) locomotion in fish optimizes the use of muscle power and body flexibility by synchronizing muscle activation with the undulating-oscillatory tail-flapping, such as Thunniform, while robotic fish are primarily designed as motion trackers rather than as efficient swimmers. In this paper, we propose a power allocation strategy (PAS) that imitates muscle rhythmic actuation, which increases the flapping amplitude by the coupling of the peduncle motion and the tail deformation. Inspired by this peduncle-tail mechanism, we developed a Direct-Drive Fish Robot (DDRFishBot). The DDRFishBot is enhanced by our developed PAS in Tail-Elastic Potential Energy (T-EPE) release by 228%, in propulsion by 45.6% and in efficiency coefficient by 16.3%. This study establishes the performance enhancement principle of exploiting tail flexibility through a simple scotch yoke mechanism, expanding the performance space of fish-inspired tail-flapping swimming robot.

This article presents a novel vision-based proprioception approach for a soft robotic finger that can estimate and reconstruct tactile interactions in terrestrial and aquatic environments. The key to this system lies in the finger's unique metamaterial structure, which facilitates omnidirectional passive adaptation during grasping, protecting delicate objects across diverse scenarios. A compact in-finger camera captures high-framerate images of the finger's deformation during contact, extracting crucial tactile data in real time. We present a volumetric discretized model of the soft finger and use the geometry constraints captured by the camera to find the optimal estimation of the deformed shape. The approach is benchmarked using a motion capture system with sparse markers and a haptic device with dense measurements. Both results show state-of-the-art accuracy, with a median error of 1.96 mm for overall body deformation, corresponding to 2.1$\%$of the finger's length. More importantly, the state estimation is robust in both on-land and underwater environments as we demonstrate its usage for underwater object shape sensing. This combination of passive adaptation and real-time tactile sensing paves the way for amphibious robotic grasping applications.

Dynamic capture is one of the most challenging issues to be solved in the field of robotics. Although robotic hands/grippers have emerged for decades, there are still few of them that can dynamically capture moving targets because the process is strongly accompanied by impact force and uncertainties in relative gripper/target locations and velocities. In this article, we present the novel design of a multitentacle gripper inspired by the motions of sea anemones. It is found that each tentacle of the sea anemone is not individually able to capture a fish but the collaboration of a larger number of tentacles can greatly enhance the overall capture ability. Based on this concept, 12 continuum arms including active and passive types are proposed and evaluated for their deformation to external forces. In addition, a deployable base, inspired by origami and Sarrus mechanisms, is utilized to change the posture of the continuum arms and drive the active arms. An inertial measurement unit is equipped to sense the impact of the dynamic targets. Finally, a series of experiments proved that the proposed multitentacle gripper could capture dynamic targets with different shapes, velocities, and collision angles, showing satisfactory capture robustness.

Soft robotic manipulators have been created and investigated for a number of applications due to their advantages over rigid robots. In minimally invasive surgery, for instance, soft robots have successfully demonstrated a number of benefits due to the compliant and flexible nature of the material they are made of. However, these type of robots struggle with performing tasks that require on-demand stiffness i.e. exerting higher forces to the surrounding environment. A number of semi-active and active mechanisms have been investigated to change and control the stiffness of soft robotic manipulators. Embedding these mechanisms in soft manipulators for spacerestricted applications can be challenging though.To better understand the inherent passive stiffness properties of soft manipulators, we propose a screw theory-based stiffness analysis for fluidic-driven continuum soft robotic manipulators. First, we derive the forward kinematics based on a parameter-based piece-wise constant curvature model. It is worth noting, our stiffness analysis can be conducted based on any freespace forward kinematic model. Then our stiffness analysis and mapping methodology is conducted based on screw theory. Initial results of our approach demonstrate the feasibility comparing computational and experimental data.

A novel concept of designing compliant actuators called “small load, low stiffness; large load, high stiffness” was applied and proven effective in human-robot interaction in our previous work. This concept was proposed based on a common scenario of interactive action where humans and some animals can adjust the stiffness of limbs in the light of tasks or contacting the environment. Based on this concept, we developed a new load-dependent nonlinear stiffness actuator (LDNSA) with a compact elastic mechanical structure. However, hysteresis is brought in inevitably along with the nonideal elastic mechanism and assembly errors, which limits the dynamic performance of the LDNSA. In this article, an equitorque discretization to implement real-time compensation is proposed to improve the classical Bouc-Wen model, commonly used to compensate for hysteresis, which is proven effective in controlling the performance of the LDNSA. Afterward, a stability analysis of the hysteresis compensation system with impedance control is also discussed as well as to guarantee the safety of the system. Finally, experiments are conducted to evaluate the performance and advantages of the LDNSA with the proposed hysteresis compensation method. The results show that the proposed model can solve the hysteresis of the LDNSA well. Note to Practitioners-Many VSAs have been developed to realize theoretically both high bandwidth and good safety due to completely decoupling stiffness and load. However, there exists some redundancy range that is rarely used in physical interaction with the environment. To avoid this redundancy, a novel load-dependent nonlinear stiffness actuator (LDNSA) was proposed in our previous work. However, hysteresis is brought in via adopting an nonideal elastic element, which is also common in many automated devices. In this article, we proposed a novel compensation algorithm to deal with the hysteresis, which can be carried out in real time. Experimental results show that compared with the Bouc-Wen model and the PD model, the proposed algorithm can solve the hysteresis of the LDNSA better. The proposed hysteresis compensation methodology can improve the performance of a rehabilitation robot for shoulder training with a modularized LDNSA.

Serial manipulator kinematics provide a mapping between joint variables in joint-space coordinates, and end-effector configurations in task-space Cartesian coordinates. Velocity mappings are represented via the manipulator Jacobian produced by direct differentiation of the forward kinematics. Acquisition of acceleration, jerk, and snap expressions, typically utilized for accurate trajectory-tracking, requires the computation of high-order Jacobian derivatives. As compared to conventional numerical/D-H approaches, this paper proposes a novel methodology to derive the Jacobians and their high-order derivatives symbolically, based on Lie theory, which requires that the derivatives are calculated with respect to each joint variable and time. Additionally, the technique described herein yields a mathematically sound solution to the high-order Jacobian derivatives, which distinguishes it from other relevant works. Performing computations with respect to the two inertial-fixed and body-fixed frames, the analytical form of the spatial and body Jacobians are derived, as well as their higher-order derivatives, without resorting to any approximations, whose expressions would depend explicitly on the joint state and the choice of reference frames. The proposed method provides more tractable computation of higher-order Jacobian derivatives, while its effectiveness has been verified by conducting a comparative analysis based on experimental data extracted from a KUKA LRB iiwa7 R800 manipulator.

This paper presents novel control techniques for passivation and stabilisation of floating-base systems with contacts, whose dynamical models comprise both joint-space, and Cartesian floating-base coordinates. The aforementioned results are achieved using both minimally model-based, and completely model-free controllers that employ power-shaping signals. Model-free control is permitted through usage of a decoupled dynamical model, procured via coordinate transformation operations. It is demonstrated that even though passive closed-loop systems are attainable without utilisation of exteroceptive feedback, global stabilisation of a floating-base robot necessitates direct usage of either measured or estimated external forces. The presented asymptotical stabilisation results pertain to both the set-point regulation, and trajectory-tracking cases, thereby ensuring suitability for static balancing, and dynamical locomotion tasks. To ensure practicability and production of feasible input signals, a variable impedance control, power-shaping term is appended to the original design, wherein it circumstantially serves as either a power-dissipating, or power-injecting element. This enhancement provably preserves closed-loop stability, by appositely shaping the system's power. Experiments involving a metamorphic, quadrupedal walking robot, corroborate the theoretical analysis, as they attest to the system's ability to stably execute locomotory tasks using a single, unified, model-free control scheme.

Endovascular aneurysm repair (EVAR) is a minimally invasive approach for abdominal aortic aneurysm (AAA) treatment. Compared to open surgery, the benefits of EVAR include faster recovery and shorter time in hospital as well as no general anesthesia (in most cases). Though EVAR has become a preferred way to treat AAA with an increasing number of procedures, there are persisting complications, e.g. stent graft migration. Suturing the stent graft to the aorta increases the displacement force necessary to move the implant. This paper describes the design of a suturing catheter for EVAR. The suturing device consist of two modules which can be inserted through the femoral arteries into the abdominal aorta where both join using an electro-magnetic connector. The positioning module provides an anchor inside the aorta for the suturing module and new sequential positions for each stitch. Our large-scale prototype is validated inside a phantom vessel made of silicone material. We are able to successfully prove the concept of this novel single-sided suturing catheter for EVAR.

Up to now the quadruped robots are equipped with the trunks which are rigid bodies or consist of two blocks connected by passive joints. This paper proposes a metamorphic quadruped robot with a moveable trunk which can implement active trunk motions, called MetaRobot I. Its trunk is constructed by a planar 6-bar linkage. Due to this linkage, it can change its trunk into multiple shapes, which give the robot the ability to imitate different animals, as well as more actions of natural quadrupeds. Specially, it can imitate the natural quadrupeds to perform trunk twisting which never been done by any quadruped robots before. Due to the twisting trunk, kinematics of this metamorphic quadruped robot is different from traditional quadruped robots. Also through the trunk twisting the body and leg workspace of the quadruped robot are increased. The mathematical model of kinematics and inner relationship between body and leg workspace and the twisting angle are analyzed in the paper. The increased body and leg workspace will help to increase the stability margins and locomotion speed. At last a simulation and an experiment on physical prototype are carried out to show the stability margins and locomotion speed impacted by the increased body workspace and leg workspace.

Minimally invasive surgery (MIS) is one of the most challenging techniques for robot designers due to the limited size of access points, the high miniaturization level, and the dexterity needed for performing surgical tasks. Conversely, only a few microfabrication technologies are currently available for developing such small-sized systems, which allow safe operations in human bodies. In order to match these challenges in MIS, both design and integration of actuation systems should proceed in parallel with an identification of most effective transmission mechanisms and kinematics. In this paper, an origami parallel module that generates two rotations and one translation is integrated with a twisting module and a compliant gripper to form a novel four-degree-of-freedom grasper. The rotational motion leads to the pitch and yaw motion of the gripper, while the translational motion is converted to a roll motion of the gripper via the twisting module that is stacked on top of the parallel module. In light of plane-symmetric properties of the origami structure in the parallel module, both inverse and forward kinematics are resolved with a geometric approach, revealing a unique joint space and a kinematic mapping of the parallel module, leading to the design of two sets of on-board actuation systems. During the analysis, bending motion of a central spring and static properties of the compliant gripper are modeled using finite-element methods. The structure of the twisting module for motion transmission of the grasper is designed and fabricated using origami folding techniques. Gripping forces of the compliant gripper are evaluated in experimental tests. Further analyses of the system performance are addressed in accordance with the scaling ratio of miniaturization and the scalability of the system is demonstrated by a millimeter-sized origami parallel module produced by the smart composite microstructure fabrication process.

In packaging industry, the duration of the carton folding plays a fundamental role in the production process; in particular in the erection process when each panel rotates around the die-pressed lines called creases. Their bending response can be very complex, depending on forming and environment conditions. The crease mechanical properties, such as geometrical parameters, temperature, moisture and folding speed, influence the overall production. It is therefore necessary to control all of these parameters, from both a theoretical and experimental point of view. About this, an experimental setup is expressly designed and built w.r.t. the rotation angle for a paper around the respective crease. The results of this research allow demonstrating the reliability of the experimental setup, the substantial negligibility of the geometrical errors and determining the number of sample so that the dispersion is compatible with the experimental errors. Then the test-ring is suitable for carton folding investigation.

Minimally invasive Surgery (MIS) is one of the most challenging fields for robot designers due to the limited size of the access points, to the high miniaturization level and to the dexterity needed for performing surgical tasks. For this reason, the integration of actuators should proceed in parallel with the identification of the most effective transmission mechanisms and kinematics. Conversely, only a few microfabrication technologies are adequate for developing small size mechanisms with safe operation in the human body. In this paper a SMA actuated, miniaturized, origami-enabled, parallel structure is presented as a versatile module for novel robotic tool in MIS, the parallel structure has been combined with a twisting module and a gripper obtaining a 4-DOFs on board actuated end-effector.

Food processing provides a lot of possibilities to apply robotics and automation. In this paper, we identify disordered and ordered states of discrete food products. The concept of Degree of Disarray is introduced. Food ordering processes such as vibratory feeders, multi-head weighers, pick and place operations are common automation in food industry to transfer products from a higher to a lower Degree of Disarray. Parts entropy is introduced to describe a product's individual state based on the symmetry categorisation. A macroscopic transitional model is presented which determines a subspace of the disordered arrangement using the eigenvectors of the largest eigenvalues of the covariance matrix. A projection into this created subspace follows. As soon as the disorder state in only one dimension is achieved, the point of disorder can be derived which finally transfers the objects into order. From here, a transformation to any order arrangement in any dimension is possible. This methodology is applied to pick and place operations and experiments are conducted.

This paper introduces a novel continuum-style robot that integrates multiple layers of compliant modules. Its essential features lie in that its bending is not based on natural compliance of a continuous backbone element or soft skeletal elements but instead is based on the compliance of each structured planar module. This structure provides several important advantages. First, it demonstrates a large linear bending motion, whilst avoiding joint friction. Second, its contraction and bending motion are decoupled. Third, it possesses ideal back-drivability and a low hysteresis. We further provide an analytical method to study the compliance characteristics of the planar module and derive the statics and kinematics of the robot. The paper provides an overview of experiments validating the design and analysis.

This work introduces a novel balance monitoring strategy for humanoid robots. The proposed method addresses the problem of ensuring the balance maintenance of a humanoid robot, through the online monitoring of its state of balance by means of a Lyapunov (energy) function. The proposed method involves the use of dynamical models accounting for both the link and motor states. Energy limits corresponding to the front and rear edges of the support polygon are computed using a closed-loop Lyapunov function. Therefore, this method focuses on the resolution of two issues through a single control scheme, namely, guaranteeing asymptotical stability of the robot at the joint level, in addition to ensuring that it maintains its dynamical balance. A mathematical proof of the previous claims, as well as of the method's validity, is provided in the paper, whereby a direct relationship between the CoP and the system's energy has been established for the first time. Experimental results of step recovery and walking tests performed on the COmpliant huMANoid (COMAN) corroborate the method's applicability and performance as a balance monitor.

This paper presents a sufficient condition to establish the existence of unique equilibrium points for three types of gravity compensation controller when applied to over-actuated systems. As compared to the existing work, this paper extends the current theory by introducing feedback gain matrices that are not constrained to being diagonal and positive definite. The inherently COmpliant huMANoid (COMAN) served as a platform for the validation of the designed gravity compensation controller that employed reference link positions. The displayed experimental results provide evidence of successful link tracking of sinusoidal references on a humanoid system composed of series elastic actuators.

This paper provides stability analyses for two different types of desired gravity compensation controllers, employing both motor and link feedback, and describes a means by which these controllers can be used to control a compliant humanoid robot in order to ensure the successful execution of walking trajectories. Given the challenging task of controlling compliant bipedal systems, owing to their possession of underactuated degrees of freedom, the full actuator and link dynamics are accounted for. The proposed walking strategy involves a process of switching between three distinct controllers which is contingent upon the force feedback provided by the force/torque sensors embedded in the robot's feet. These controllers were tuned using a simulation model of the robot and were then implemented on the compliant COMAN legs, whose performance of walking confirms the controllers' stability, in addition to the walking scheme's efficacy.

Performance of a parallel manipulator heavily relies on its position/orientation resolution. Without a good resolution the manipulator is difficult to achieve a high stiffness. Therefore how to obtain the required resolution is a basic issue to design a parallel manipulator. This paper presents a method to solve the problem. Firstly, the mathematical definition of the position/orientation resolution is given. Then we discuss how to calculate them using Rayleigh quotient. And the design optimization problem is formulated. Fundamental concepts of the method are illustrated through a 3-RRR planar parallel manipulator. The design process to achieve an optimized task space of the required pose resolution is also demonstrated in the example.

This paper presents models for description and identification of various cartons in their discrete states, and proposes a new approach to describe the transformation of configuration states during carton manipulation in a packaging process. The method makes use of matrix operations which can be used to identify and model the steps and changes in carton manipulation at different stages of a packaging process. This gives an analytical way of presenting and identifying information of a carton and of modeling carton packaging manipulation and presents a new way for carton packaging automation.

This paper presents the control architecture and preliminary experimental results of a high performance parallel robot used for ankle rehabilitation. The goal of this work was to design suitable control algorithms for diagnostic, training and rehabilitation of the ankle in presence of musculoskeletal injuries. A position control scheme is used for patient-passive exercises while an admittance control technique is used to perform patient-active exercises with and without motion assistance. The design of the control algorithms is based on the analysis of the rehabilitation protocol taking into account the dynamics of the system and the dynamics of the interaction between the human and the robot. Electromyographic (EMG) signals are used to evaluate patient's effort during training/exercising. The results indicate the great potential of the rehabilitation device as a tool to fasten and improve the ankle therapies outcome.

Hydraulic actuators are characterized by fast dynamics, high power density, high stiffness, large output force/torque, and in recent years are becoming increasingly attractive in the field of robotics. This paper presents the study of a 3-way proportional valve controlled, spring assisted electro-hydraulic rotary actuator, which consists of a 3-way proportional valve, a linear cylinder and a reciprocal spring. The operating principle is presented and a mathematical model is developed. Comparison analysis is made between the new actuator and a traditional one with an application to a hydraulically actuated legged robot.

This paper investigates the kinematics of spin-rolling motion of rigid objects. This paper does not consider slipping but applies a Darboux frame to develop kinematics of spin-rolling motion, which occurs in a nonholonomic system. A new formulation of spin-rolling motion of the moving object is derived in terms of contravariant vectors, rolling velocity, and geometric invariants, including normal curvature, geodesic curvature, and geodesic torsion of the respective contact curve. The equation is represented with geometric invariants. It can be readily generalized to suit both arbitrary parametric surface and contact trajectory and can be differentiated to any order. Effect of the relative curvatures and torsion on spin-rolling kinematics is explicitly presented. The translation velocity of an arbitrary point on the moving object is also derived based on the Darboux frame.

This paper adopts a coordinate-free approach to investigate the kinematics of rigid bodies with rolling contact. A new equation of angular velocity of the moving body is derived in terms of the magnitude of rolling velocity and two sets of geometric invariants belonging to the respective contact curves. This new formulation can be differentiated up to any order. Furthermore, qualitative information about trajectory planning can be deduced from this equation if the characteristics of rolling objects and the motion are taken into consideration.

This paper presents the mechanical design of an ankle rehabilitation robotic device based on a 2-dof, redundantly actuated parallel mechanism. The parallel mechanism introduced in this paper has the advantage of mechanical and kinematic simplicity when compared to existing platforms while at the same time it is fully capable of carrying out all the exercises required by ankle rehabilitation protocols. The proposed device makes use of actuation redundancy to eliminate singularity and greatly improve the workspace dexterity. In addition, the requirements for high torque capacity and back-drivability are satisfied with the employment of a custom made cable driven linear electric actuator that combines the high force capacity with excellent back-drivability. The analysis undergoes the optimal design towards the maximization of manipulator workspace, dexterity, torque output and compactness of the device. Finally, the performance of the custom linear actuator and the prototype of the rehabilitation device are shown.

This paper introduces for the first time a metamorphic palm and presents a novel multifingered hand, known as Matahand, with a foldable and flexible palm that makes the hand adaptable and reconfigurable. The orientation and pose of the new robotic hand are enhanced by additional motion of the palm, and workspace of the robotic fingers is complemented with the palm motion. To analyze this enhanced workspace, this paper introduces finger-orientation planes to relate the finger orientation to palm various configurations. Normals of these orientation planes are used to construct a Gauss map. Adding an additional dimension, a 4-D ruled surface is generated to illustrate orientation and pose change of the hand, and an orientation-pose manifold is developed from the orientation-pose ruled surface. The orientation and workspace analysis are further developed by introducing a triangular palm workspace that evolves into a helical surface and is further developed into a 4-D representation. Simulations are presented to illustrate the characteristics of this new dexterous hand.

In automatic assembly, a vibratory bowl feeder plays a crucial role for reorienting the parts and feeding them into an assembly process. Taking the bowl as a platform and three prismatic flat-spring supports as spatial compliant legs and based on the continuum dynamics, this paper examines the bowl feeder from the point-of-view of a compliant platform device by applying von Mises' compliance study to each of the flat-spring legs and establishes a screw system of each leg. The compliance and Jacobian matrix of the bowl feeder are presented, the potential and kinetic energies are analyzed, and the dynamics models are established, leading to the characteristic equations of the compliant platform device. This generates for the first time the shape function integrated stiffness matrix and inertia matrix. This paper further analyzes the two characteristic equations of both a simplified system and a generalized system, implements the comparative study of the system natural frequencies between the two system models, and presents the stability analysis involving the system hysteresis damping. The effect of platform design parameters on the natural frequencies of the system under damping is identified and modal analysis of the system is carried out according to different forms of the excitation force. This paper presents a comprehensive study of the dynamics of this kind of compliant devices.

This paper investigates the geometric characteristics of the sun-worm and the stationary internal toroidal gear in toroidal drive, explores the three dimensional modeling, carries out kinematical simulation and interference detection for this kind of drive. Further, the dynamical simulation is also developed. Finally, the NC manufacturing simulation is propose that solves cutter selection and undercutting elimination for the practical NC manufacturing of the stationary internal toroidal gear.

A flexure-based compliant parallel manipulator (FCPM) is a kind of compliant mechanism characterized by a complicate topological structure and multiple degrees of freedom (DOFs). Compared with its rigid-counterpart, a FCPM becomes more complicate in its mobility analysis. In this paper, the screw theory is applied to the mobility analysis of our FCPM as an instance of general FCPM. Firstly, the compliance matrices of both compliant elements and the whole mechanism are calculated by using adjoint transformation of compliance matrix between different coordinate frames. Secondly, the mobility characteristics of the FCPM is investigated by proposing a concept of "primary mobility of a FCPM" and a method of quantifying the primary mobility of the FCPM providing that the compliance matrix of the manipulator should be calculated primarily. The theoretical result reveals that mobility characteristics of the FCPM with current design parameters can satisfy the designer's original desire

In this work we construct a simple dynamical model for vibratory bowl feeders. The symmetrical arrangement of the springs supporting the bowl allow us to predict a simple structure for the stiffness matrix of the system. The cylindrical symmetry of the bowl itself then means that the linearized rigid body dynamics of the system can be simplified to a 2-dimensional system. The solutions to this system are elliptical motions of the bowl, vibrating about the symmetry axis and along it at the same time. We are able to find a condition for the system to be at resonance. There is some debate about how the parts move up the helical track inside the bowl. We are able to show that one alternative, a “slip-stick” motion, is unlikely.