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The functional reliability of the vehicle latch is very important and is determined by the internal mechanism's motion stability. In this paper, a novel compliant mechanism constructed with a novel compliant joint is applied to the vehicle latch, and multiple mode motions of the mechanism realize the newly added electric power release function. The repeatability of mechanism trajectories and phase diagrams of several different periodic motions is creatively regarded as the stability of the compliant mechanism. In this compliant mechanism, the endpoint of the groove-coupler is chosen as a characteristic point and the compliant joint's spring stiffness k T is taken as the key parameter to obtain trajectories and phase diagram. It is found that all cycle overlapping phase diagrams possess intuitively good repeatability, except in two locally specific regions. Then, Wolf's numerical calculation method of Lyapunov exponents is utilized to analyze the motion stability of the compliant mechanism. An appropriate range (1.0–1.05 N mm/°) of the joint stiffness k T is obtained, satisfying the stability criterion. Finally, characteristic point trajectory and functional experiments with k T = 1 N mm/° are conducted to verify the motion stability of the compliant mechanism. The method of mechanism motion stability analysis by means of Lyapunov exponents can be applied to other under-actuated mechanisms. [ABSTRACT FROM AUTHOR]

The article describes two versions of a gripper's fingers that utilize compliant revolute kinematic pairs in their operation. The goal in designing the gripper was to create a universal structure that allows for easy adjustment of torsional stiffness and maximum rotation angle as needed. Two compliant revolute joints were proposed and applied in the creation of two versions of the gripper’s fingers. In both joints, one geometric parameter was selected for variation. Finite element analysis was conducted to calculate the statics within the parameter range. Based on the calculations, stiffness charts were created as a function of parameter values. Subsequently, using 3D printing technology in resin, two gripper fingers were produced. Experimental tests were conducted on these fingers to assess their torsional stiffness. The computational and experimental results were compared. The designed fingers are best suited for pneumatic grippers. When using them, complex force control can be eliminated because the gripping force increases gradually in accordance with the compliance of the gripper, rather than abruptly. The fingers also exhibit different stiffness characteristics depending on the direction of the grip - outward or inward.

The article describes two versions of a gripper's fingers that utilize compliant revolute kinematic pairs in their operation. The goal in designing the gripper was to create a universal structure that allows for easy adjustment of torsional stiffness and maximum rotation angle as needed. Two compliant revolute joints were proposed and applied in the creation of two versions of the gripper's fingers. In both joints, one geometric parameter was selected for variation. Finite element analysis was conducted to calculate the statics within the parameter range. Based on the calculations, stiffness charts were created as a function of parameter values. Subsequently, using 3D printing technology in resin, two gripper fingers were produced. Experimental tests were conducted on these fingers to assess their torsional stiffness. The computational and experimental results were compared. The designed fingers are best suited for pneumatic grippers. When using them, complex force control can be eliminated because the gripping force increases gradually in accordance with the compliance of the gripper, rather than abruptly. The fingers also exhibit different stiffness characteristics depending on the direction of the grip-outward or inward. [ABSTRACT FROM AUTHOR]

Compliant joints have significant advantages compared to rigid-body hinges due to a monolithic design and the absence of friction, which prevents effects like wear, backlash, and stick-slip behavior. However, the loading capability is often limited and the support stiffness generally decreases during rotation. A new design principle called closed form pressure balancing has been proposed as a solution to improve these limitations. By using an incompressible fluid as the main compliant element, the support stiffness becomes independent of rotation and buckling no longer limits the loading capability. This work analyzes the fundamental working principle behind closed form pressure balancing and introduces a 2D design model to determine stiffness properties. The design model is validated with a finite element model and used to construct an optimization strategy for optimum joint performance. Additionally, a conversion model and some practical considerations are presented for the transition to a 3D design model. [ABSTRACT FROM AUTHOR]

Compliant joint plays a vital role in micro-positioning systems, robotics, and precision instruments due to its friction-free and fine motion. However, the existing joints are limited in range of motions and degrees of freedom. Thus, this paper proposes a new compliant joint (CJ) which is inspired from the dragonfly's wing. The proposed joint can provide two translational motions with a large range of motion. The CJ has six curvilinear shapes which are arranged in a parallel architecture. Besides, the proposed joint has a thin-wall structure to enlarge the deformation capacity. Based on the Euler–Bernoulli beam theory, the analytical model is established to describe the stiffness and displacement of the joint. Effects of the joint's geometries on the stiffness are investigated. The deformation and load capacities of the CJ are determined. The results showed that the displacement of the CJ in the y-axis is increased to 43.5% and 5.95% in comparison with the circular notch hinge and rectangular flexure hinge, respectively. Besides, the results determined that the displacements of the CJ in the x-axis are 58.57 times and 51.25 times larger than those of the traditional flexure hinges, respectively. The errors between the simulation, analytical model, and experiment are around 5%. It means that the closed-form model is validated for the proposed joint. The proposed CJ is a potential joint for micro-positioning technologies. [ABSTRACT FROM AUTHOR]

Limited by rigid instruments, traditional open curettage of bone cysts requires large incisions and the removal of substantial amounts of healthy bone tissue to approach the lesion. This causes a lengthy recovery period with an increased risk for complications. While other less invasive methods have been suggested, none have been accepted as standard treatment modalities, and many of them have not been applied beyond academic studies. We propose a fully robotic compliant joint-based endoscopic surgery system capable of the minimally invasive removal of bone cysts. A drilling robot optimized to bend removes the lesion, while an endoscopic robot provides visual feedback as well as suction and irrigation for cleaning the inner bone. Two leader devices are used to precisely control the movement of each robot in a leader-follower configuration. The performance of the proposed system was evaluated in a series of experiments on animal femurs. [ABSTRACT FROM AUTHOR]

Insect wings are deformable airfoils, in which deformations are mostly achieved by complicated interactions between their structural components. Due to the complexity of the wing design and technical challenges associated with testing the delicate wings, we know little about the properties of their components and how they determine wing response to flight forces. Here, we report an unusual structure from the hind-wing membrane of the beetle Pachnoda marginata. The structure, a transverse section of the claval flexion line, consists of two distinguishable layers: a bell-shaped upper layer and a straight lower layer. Our computational simulations showed that this is an effective one-way hinge, which is stiff in tension and upward bending but flexible in compression and downward bending. By systematically varying its design parameters in a computational model, we showed that the properties of the double-layer membrane hinge can be tuned over a wide range. This enabled us to develop a broad design space, which we later used for model selection. We used selected models in three distinct applications, which proved that the double-layer hinge represents a simple yet effective design strategy for controlling the mechanical response of structures using a single material and with no extra mass. The insect-inspired, one-way hinge is particularly useful for developing structures with asymmetric behavior, exhibiting different responses to the same load in two opposite directions. This multidisciplinary study not only advances our understanding of the biomechanics of complicated insect wings but also informs the design of easily tunable engineering hinges. [ABSTRACT FROM AUTHOR]

In robotics, the variable stiffness joints have been developed as an alternative to include flexibility to a rigid mechanism. Variable Stiffness Joint (VSJ) allows for varying the stiffness in a mechanism during the performance of a trajectory. The development of this joint has increased, and various applications have emerged, most to improve human-robot interaction. This paper presents a VSJ based on the principle of antagonistic springs with a set of gears and racks that allow the extension or compression of the springs. The joint provides constant torque or variable torque to obtain a constant or variable force at the output of the link, so a relationship is between the torque provided by the spring's effort and the output force; however, it is possible to achieve a desired variable force with this joint design. Simulations are realized to obtain the behavior for both a constant and a variable force. [ABSTRACT FROM AUTHOR]

Constant-force mechanisms can be used for gravity counterbalance and force regulation. While many constant-force mechanisms have been designed, most of them have a limited range of force adjustment, which brings very limited capability to maintain an equilibrium state when load changes. In this paper, a novel design of reconfigurable constant-force mechanism is proposed. The new design is inspired by a variable stiffness mechanism, which can work in a similar way as the hinged lever, but take a compact space. Moreover, the design allows to adjust the configuration parameters achieving a large range of the equilibrium state adjustment. Mathematical models are developed to simulate the equilibrium performance changed with configuration parameters. A prototype is constructed and validates the working principle of the design. A design case is included to show the application of the mechanism in a passive assistive upper-body exoskeleton. [ABSTRACT FROM AUTHOR]

The nonlinear stiffness actuator (NSA) is a type of compliant joint with variable stiffness that is necessary for human-machine collaboration and has been the focus of extensive research attention. This academic work presents the principle of a torsion spring-connected nonlinear stiffness actuator (TSNSA), a NSA suitable for implementing revolute motions, which contrasts with existing NSAs that often have bulky mechanisms and are affected by a limited range of movement. It has a split sleeve, disc springs, and cam mechanisms (CMs) that when correctly configured, can passively and actively adjust stiffness, where the speed of stiffness regulation can be effectively improved. The mathematical model of a split sleeve inserted into a torsion spring is designed to analyze the behavior of mechanical components. Furthermore, a detailed CM profile has been designed to obtain the desired nonlinear stiffness. Its theoretical analysis includes numerical simulations with results consistent with the desired deflection-torque profile. [ABSTRACT FROM AUTHOR]

Background: The exoskeleton for lower limb rehabilitation is an uprising field of robot technology. However, since it is difficult to achieve all the optimal design values at the same time, each lower extremity exoskeleton has its own focus.Objective: This study aims to develop a modular lightweight lower extremity exoskeleton (MOLLEE) with novel compliant ankle joints, and evaluate the movement performance through kinematics analysis.Methods: The overall structure of the exoskeleton was proposed and the adjustable frames, active joint modules, and compliant ankle joints were designed. The forward and inverse kinematics models were established based on the geometric method. The theoretical models were validated by numerical simulations in ADAMS, and the kinematic performance was demonstrated through walking experiments.Results: The proposed lower extremity offers six degrees of freedom (DoF). The exoskeleton frame was designed adjustable to fit wearers with a height between 1.55 m and 1.80 m, and waist width from 37 cm to 45 cm. The joint modules can provide maximum torque at 107 Nm for adequate knee and hip joint motion forces. The compliant ankle can bear large flexible deformation, and the relationship between its angular deformation and the contact force can be fitted with a quadratic polynomial function. The kinematics models were established and verified through numerical simulations, and the walking experiments in different action states have shown the expected kinematic characteristics of the designed exoskeleton.Conclusions: The proposed MOLLEE exoskeleton is adjustable, modular, and compliant. The designed adjustable frame and compliant ankle can ensure comfort and safety for different wearers. In addition, the kinematics characteristics of the exoskeleton can meet the needs of daily rehabilitation activities. [ABSTRACT FROM AUTHOR]

Compliant joints are flexible elements that allow displacement due to the elastic deformations they experience under the action of external loading. The flexible parts responsible for these displacements are known as flexure hinges. Displacement, or motion range, in compliant joints depends on the stiffness of the flexure hinges and can be tailored through various parameters, including the overall dimensions, the base material, and the distribution within the hinge. Considering the distribution, we propose the stiffness modification of a compliant cross-axis joint via the use of lattice mechanical metamaterials. Due to the wide range of parameters that influence the stiffness of a lattice, different machine learning algorithms (artificial neural networks, support vector machine, and Gaussian progress regression) were proposed to forecast these parameters. Here, the machine learning algorithm with the best forecasting was the Gaussian progress regression; this algorithm has the advantage of well-tuning even with small regression databases, allowing these functions to more easily adjust to suit specific data, even if the dataset is small. Hexagonal, re-entrant, and square lattices were studied as flexure hinges. For each, the effect of the unit cell size and its orientation with respect to the principal axis on the effective stiffness were studied via computational and laboratory experiments on additively manufactured samples. Finite element predictions resulted in good agreement with the experimentally obtained data. As a result, using lattice-flexure hinges led to increments in displacement ranging from double to ten times those obtained with solid hinges. The most suitable machine learning algorithm was the Gaussian progress regression, with a maximum error of 0.12% when compared to the finite element analysis results. [ABSTRACT FROM AUTHOR]

Thanks to their outstanding properties, in the last few years Dielectric Elastomer Actuators (DEAs) have increasingly attracted the interest of the scientific community and generated a surge in the effort devoted to their industrialization. Compared to conventional actuator systems, DEAs are based on inexpensive and widely available polymeric materials, which make them potentially attractive from a market perspective. However, DEA systems with a given layout and dimensions have a fixed force-stroke response that is only suitable for a specific load profile. This leads to a wide variety of designs combined with small production volumes and high costs, limiting the competitive advantage. This work addresses this issue by proposing a combination of DEA systems with compliant scissor linkage transmission mechanisms, which provide linear stroke and force scaling and simultaneously maintain performance optimization by leaving the convertible energy density of the DEA unaffected. For this purpose, three systems are designed, based on a same strip-shaped DEA combined with inclined buckled beam biasing mechanisms. Two of the systems are coupled with scissor linkages that offer transmission ratios of 3:1 and 1:3, respectively, to adapt the system to different load profiles. The system design is explained in detail, and the functional principle is validated through experiments. [ABSTRACT FROM AUTHOR]

A three-legged compliant parallel mechanism (3L-CPM) achieves fully decoupled motions when its theoretical 6 × 6 stiffness/compliance matrix is a diagonal matrix, which only contains diagonal components, while all non-diagonal components are zeros. Because the motion decoupling capability of 3L-CPMs is essential in the precision engineering field, this paper presents the fundamental criteria for designing 3L-CPMs with fully decoupled motions, regardless of degrees-of-freedom and the types of flexure element. The 6 × 6 stiffness matrix of a general 3L-CPM is derived based on the orientation of each flexure element, e.g., thin/slender beam and notch hinge, etc., and its relative position to the moving platform. Based on an analytical solution, several requirements for the flexure elements were identified and needed to be satisfied in order to design a 3L-CPM with a diagonal stiffness/compliance matrix. In addition, the developed design criteria were used to analyze the decoupled-motion capability of some existing 3L-CPM designs and shown to provide insight into the motion characteristics of any 3L-CPM. [ABSTRACT FROM AUTHOR]

Thanks to their outstanding properties, in the last few years Dielectric Elastomer Actuators (DEAs) have increasingly attracted the interest of the scientific community and generated a surge in the effort devoted to their industrialization. Compared to conventional actuator systems, DEAs are based on inexpensive and widely available polymeric materials, which make them potentially attractive from a market perspective. However, DEA systems with a given layout and dimensions have a fixed force-stroke response that is only suitable for a specific load profile. This leads to a wide variety of designs combined with small production volumes and high costs, limiting the competitive advantage. This work addresses this issue by proposing a combination of DEA systems with compliant scissor linkage transmission mechanisms, which provide linear stroke and force scaling and simultaneously maintain performance optimization by leaving the convertible energy density of the DEA unaffected. For this purpose, three systems are designed, based on a same strip-shaped DEA combined with inclined buckled beam biasing mechanisms. Two of the systems are coupled with scissor linkages that offer transmission ratios of 3:1 and 1:3, respectively, to adapt the system to different load profiles. The system design is explained in detail, and the functional principle is validated through experiments.

Compliant joints are flexible elements that allow displacement due to the elastic deformations they experience under the action of external loading. The flexible parts responsible for these displacements are known as flexure hinges. Displacement, or motion range, in compliant joints depends on the stiffness of the flexure hinges and can be tailored through various parameters, including the overall dimensions, the base material, and the distribution within the hinge. Considering the distribution, we propose the stiffness modification of a compliant cross-axis joint via the use of lattice mechanical metamaterials. Due to the wide range of parameters that influence the stiffness of a lattice, different machine learning algorithms (artificial neural networks, support vector machine, and Gaussian progress regression) were proposed to forecast these parameters. Here, the machine learning algorithm with the best forecasting was the Gaussian progress regression; this algorithm has the advantage of well-tuning even with small regression databases, allowing these functions to more easily adjust to suit specific data, even if the dataset is small. Hexagonal, re-entrant, and square lattices were studied as flexure hinges. For each, the effect of the unit cell size and its orientation with respect to the principal axis on the effective stiffness were studied via computational and laboratory experiments on additively manufactured samples. Finite element predictions resulted in good agreement with the experimentally obtained data. As a result, using lattice-flexure hinges led to increments in displacement ranging from double to ten times those obtained with solid hinges. The most suitable machine learning algorithm was the Gaussian progress regression, with a maximum error of 0.12% when compared to the finite element analysis results.

A three-legged compliant parallel mechanism (3L-CPM) achieves fully decoupled motions when its theoretical 6 × 6 stiffness/compliance matrix is a diagonal matrix, which only contains diagonal components, while all non-diagonal components are zeros. Because the motion decoupling capability of 3L-CPMs is essential in the precision engineering field, this paper presents the fundamental criteria for designing 3L-CPMs with fully decoupled motions, regardless of degrees-of-freedom and the types of flexure element. The 6 × 6 stiffness matrix of a general 3L-CPM is derived based on the orientation of each flexure element, e.g., thin/slender beam and notch hinge, etc., and its relative position to the moving platform. Based on an analytical solution, several requirements for the flexure elements were identified and needed to be satisfied in order to design a 3L-CPM with a diagonal stiffness/compliance matrix. In addition, the developed design criteria were used to analyze the decoupled-motion capability of some existing 3L-CPM designs and shown to provide insight into the motion characteristics of any 3L-CPM.

Compliant joints can provide safer physical human–robot interaction. To effectively balance the response bandwidth and output impedance, variable stiffness joints have been studied by many researchers. Leaf spring-based variable stiffness joint (LSVSJ) has the advantages of easy construction and large stiffness range. This article presents the design and validation of a novel LSVSJ with reconfigurability (LSJR). Compared with most of the existing LSVSJ, this novel LSJR ensures the contact performance between the roller and the leaf spring, uses a novel effective length adjustment mechanism, and provides multiple stiffness ranges. The compliance of the LSJR is generated by leaf springs. The spring is bent by two rows of rollers integrated on an adjustable slider, where the distance between the rollers can be changed so as to achieve a tighter contact between the roller and the spring. The effective length of the spring can be adjusted by changing the position of the slider locating at the intersection between a straight rail and an arcuate rail. A reconfigurable number of leaf springs provide six different stiffness ranges (e.g., 138.55–396.08 N·m/rad for single leaf spring, and 384.56–1222.60 N·m/rad for a combination of three leaf springs). By integrating a high-resolution angle sensor, the LSJR can also measure the joint torque. Moreover, the hollow shaft structure of the joint is beneficial for passing cables through it. Experiments were performed to measure the stiffness of the LSJR under different configurations, validate its efficacy in unexpected collisions, and investigate its potential to be a one-degree-of-freedom torque sensor. [ABSTRACT FROM AUTHOR]

This paper proposes a new butterfly-inspired compliant joint by combining a butterfly's profile and a foldable mechanism. The joint can achieve three degrees of freedom in its fabrication plane, including two translations in the x- and y-axes and a rotary motion around the z-axis. Equivalent spring stiffness of the joint is easy to be adjusted by adopting a foldable mechanism, while a butterfly's profile gives better compliance. Closed-form model of the joint is established to calculate stiffness, displacement, and rotational angle. Performances and effectiveness of the proposed joint are verified by comparing with other joints. A prototype is fabricated, and experiments are conducted. The results show a good agreement between the analytical model, simulation, and experiment. Compared with a conventional rectangular flexure joint in terms of bending displacement and compressive displacement, the results found that performances of the joint are greatly improved. Bending displacement and angular displacement of the joint are increased by up to 14.6% and 12.6%, respectively. The proposed joint can be considered as a potential candidate for a precise positioning system. [ABSTRACT FROM AUTHOR]

In this paper, a novel active compliant joint for robotic and microdisplacement applications is investigated numerically and experimentally. The proposed actuator structure is simple and possesses a higher energy density compared to the available actuators. Experimental tests are performed employing the shape memory behavior of NiTi alloy by the electric current as a heating source. To verify the actuator performance, numerical models are simulated in a nonlinear finite element program through employing a user subroutine according to experimental tests. Finite element implementation of the proposed actuator is performed based on the constitutive equations developed in Boyd–Lagoudas phenomenological model. Comparing the test and numerical results revealed that the numerical model is successful in predicting the actuator response. Finally, based on the verified numerical model, the effects of different parameters, e.g. the compression spring stiffness on the actuator performance are studied, and an optimal design for the actuator structure is proposed. [ABSTRACT FROM AUTHOR]

SUMMARY: This paper discusses the concept and parameter design of a robust stair-climbing compliant modular robot, capable of tackling stairs with overhangs. Geometry modifications of the periphery of the wheels of our robot helped in tackling overhangs. Along with establishing a concept design, the robust design parameters are set to minimize performance variations. The Grey-based Taguchi method is applied to provide an optimal setting for the design parameters of the robot. The robot prototype is shown to have successfully scaled stairs of varying dimensions, with overhang, thus corroborating the analysis performed. [ABSTRACT FROM AUTHOR]

Human safety represents the key requirement in physical human-robot interaction (pHRI). However, the majority of current research works focus on the safety evaluation. There is no definite way to design a robot that not only meets the performance but also has inherent safety. A humanoid robot for human joint movement rehabilitation is developed, to fulfill the requirement of both safety and its performance. A nonlinear model of human-robot collision with effective mass and stiffness of robot's end-effecter (EE) is proposed. An important parameter involved in the model is the joint stiffness of the robot, which has an inherent direct effect on the safety. The influence of joint compliance on the modal frequencies is analyzed, and the kinematic performance of the robot is estimated roughly by the lowest order modal frequency. The design method of compliant joint stiffness is put forward, which can balance the safety and kinematics performance requirements. When the compliance is utilized intentionally in joints to improve safety, the question whether or not rigid performance of compliant joint can be achieved or approached by control is arose naturally. Such a challenge is addressed by the cascade control, where outer position loop with link-side position feedback is constructed. Here, restoring torque in the elastic transmission is taken as virtual control that is, in turn, set as the reference command of the inner torque loop. Intuitively, once the virtual control is reproduced as rapidly as possible in the inner torque loop, quasi-rigid performance is exhibited in the outer position loop as if there were no series elasticity in compliant joint. The stability criterion is derived, and the virtual stiffness and dynamic performance are examined. Finally, experiments are performed to validate effectiveness of the suggested control scheme. [ABSTRACT FROM AUTHOR]

Compliant joints are the basis of compliant mechanisms. In this paper, a variable stiffness compliant joint is presented. By sliding the sliders on the flexure segments, the effective length can be changed, which leads to the variation of the joint's stiffness. The closed-form model is given, and the equations needed to calculate the equivalent spring constant are derived. Using these equations, the joint is analyzed theoretically. Furthermore, the model is verified using finite element analysis (FEA). The results obtained through two different ways coincide with each other very well, and the results show that the joint's stiffness can change in a large range. Since the sliders can slide both symmetrically and unsymmetrically, the joint is discussed in two different situations. Finally, an example of application is given, the mechanism can reach different positions by changing the joint's stiffness when the external loads are given. [ABSTRACT FROM AUTHOR]

To improve the patient transfer skill of nursing education students, we developed a robot patient that can simulate three categories of patients: 1) patients whose movements are affected by paralysis; 2) patients whose movements are sensitive to pain with painful expression; and 3) patients whose movements are constrained by medical devices. By practicing with the robot patient, nursing students can learn the skills required for interacting with various patients. To simulate trunk movements of these different patients, novel waist and hip joints with hardware-inherent compliance and force-sensing capability were proposed. In addition, control methods were developed and the parameters were tuned based on actual patient videos. To evaluate the developed robot, nursing teachers performed trials of transferring the robot patient as they would transfer an actual patient. The nursing teachers scored the robot patients based on a checklist. Moreover, subjective evaluations of a questionnaire were performed by the nursing teachers. The results showed that the nursing teachers performed most of the required skills of the checklist and agreed regarding the learning effectiveness of the robot. They recommended training nursing students using the robot patient in the questionnaire. Finally, hugging speed comparison showed that the nurses slow down the speed when dealing with a robot patient with painful expression. [ABSTRACT FROM PUBLISHER]

Variable stiffness actuator (VSA) can significantly improve the dynamic performance of robots and ensure safety in human robot interaction. In this paper, a novel structure-controlled VSA which achieves a lower minimal stiffness while the size and load capacity remain unchanged is introduced. Stiffness variation is implemented by changing the effective length of parallel-assembled-folded serial leaf springs presented in this paper, which makes the adjustment of stiffness easier and driven by an independent motor. A modified analytical model of joint stiffness is built, which takes the gap between leaf springs and rollers into consideration. Experiments prove that the modified model is more accurate comparing with the ideal model which ignores the gap. Further analyses show that the gap can even make serious impacts on leaf spring-based structure-controlled VSA in other performances such as deformability and energy capacity. [ABSTRACT FROM AUTHOR]

This paper introduces a Compliant thin-walled joint (CTWJ) that expands the group of existing compliant joints. The CTWJ design is based on the nonlinear geometry of the zygoptera animal. With a thin-walled structure, the CTWJ allows a considerably large range of motion in the x-and-y axes. In addition, the thin-walled structure is then filled by polydimethylsiloxane material to reinforce the stiffness of the CTWJ. First, design of experiment methodology is used for the sensitive analysis of the width and the thickness to the strain of joint. The range of motion, the strain, the buckling behavior, and the first natural frequency of CTWJ are investigated via finite element analysis and experiments. The behavior of the CTWJ is subsequently compared with the conventional compliant joints to realize the efficient performance of the CTWJ. The results revealed that the CTWJ has a range of motion and strain energy larger than those of traditional compliant joints. Finally, an example of vibration isolator is modeled by using the CTWJ as planar spring. It is believed that the CTWJ has a great potential for the development of compliant mechanisms in terms of large range of motions in mutliple axes. [ABSTRACT FROM AUTHOR]

In the last decades, there have been great efforts in the development of advanced polyarticulated prosthetic hands; in contrast, prosthetic wrists have drawn less interest. Nevertheless, increasing the dexterity of the wrist improves handling skills because the wrist allows the prepositioning of the hand before carrying out a task, avoiding the onset of unwanted trunk or shoulders compensatory movements and potential onset or exacerbation of articular injuries. This study presents a novel 2-degree-of-freedom prosthetic wrist module with active pronation/supination and passive elastic flexion/extension. This system is suitable to be included in hand prostheses to improve anthropomorphism and produce a more physiological motion. The first submodule within the socket is able to rotate a prosthetic hand and an external load of 3 kg at 2.6 rad/s. The second one can guarantee a range of motion of ±75° with a centering elastic torque (compliant mode) or it can keep firms grasps (fixed mode). Compliant mode is based on a Scotch-Yoke mechanism converting wrist flexion/extension into the linear motion of a crossbeam acting on compression springs, while fixed mode is achieved by means of a piston that can be engaged/disengaged. The whole module fits with anthropometry and the modular design ensures the proposed system can be used in a stand-alone way and adapted to different hand prostheses. This device is expected to favor a more physiological dexterity with respect to simpler fixed prostheses that can potentially induce harmful motion of body districts not naturally involved in the reaching and grasping tasks., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Robotic operations need to be safe for unpredictable contacts. Joints with passive compliance with springs can be used for soft robotic contacts. However the joints cannot measure external collision forces. In this investigation was developed one passive compliant joint which have soft contacts with external objects and measurement capabilities. To ensure it, conductive silicone rubber was used as material for modeling of the compliant segments of the robotic joint. These compliant segments represent embedded sensors. The conductive silicone rubber is electrically conductive by deformations. The main task was to obtain elastic absorbers for the external collision forces. These absorbers can be used for measurement in the same time. In other words, the joint has an internal measurement system. Adaptive neuro fuzzy inference system (ANFIS) was used to estimate the safety level of the robotic joint by head injury criteria (HIC). [ABSTRACT FROM AUTHOR]

This paper presents the design and development of a novel compliant safe joint (CSJ). The principle of operation of the CSJ is based on a cam-like transmission mechanism, which we call the bridge. The cam profile on the stationary bridge is designed to have multiple regions, which allow the CSJ to passively achieve multiple working states. The proposed joint behaves as a normal rigid joint when the load is smaller than a preset threshold, shifts into the flexible state when the load exceeds the threshold, and switches into the free state in which the motion cannot be transmitted from the motor to the output shaft. In order to achieve a compact modular assembly, the joint's components are designed to have the shape of a hollow cylinder and to be installed around the motor. We analyze how the key dimension parameters affect the torque threshold and the joint's stiffness. Experiments are conducted to validate the working principle and verify the performance of the joint. [ABSTRACT FROM PUBLISHER]

Stiffness is an important element in the model of a parallel manipulator. A complete stiffness analysis includes the contributions of joints as well as structural elements. Parallel manipulators potentially include both actuated joints, passive compliant joints, and zero stiffness joints, while a leg may impose constraints on the end-effector in the case of lower mobility parallel manipulators. Additionally, parallel manipulators are often designed to interact with an environment, which means that an external wrench may be applied to the end-effector. This paper presents a Jacobian-based stiffness analysis method, based on screw theory, that effectively considers all above aspects and which also applies to parallel manipulators with non-redundant legs. [ABSTRACT FROM AUTHOR]

The conventional linkage mechanisms with compliant joint have been widely studied and implemented for increasing the adaptability of the mechanism to external contacts. However, the analysis of how compliant joints in linkage mechanism can reduce the energy consumption isn't still studied deeply. In a mobile service robot head, the actions of blinking the eyes and moving the eyeballs are realized by the planar linkage mechanism respectively. Therefore, minimizing the driving torques through motion trajectories for the linkage mechanism, which will be beneficial to extend the working time for mobile service robots. The dynamic modeling of the linkage mechanism with springs-loaded compliant joint is established. An optimization procedure for obtaining the optimal parameters of springs is proposed for minimizing the max value of driving torques within a range of desired operating conditions. The Simulations prove that the linkage mechanism with compliant joints can effectively reduce the driving torques, and reduce the energy consumption consequently. The framework can also be applied in other similar applications to reduce the driving torque and save energy. Compared with previous efforts, this is the first attempt that the linkage mechanism with complaint joint is applied in the robot head for reducing the driving torque. [ABSTRACT FROM AUTHOR]

The field of exoskeletons and wearable devices for walking assistance and rehabilitation has advanced considerably over the past few years. Currently, commercial devices contain joints with stiff actuators that cannot adapt to unpredictable environments. These actuators consume more energy and may not be appropriate for human–machine interactions. Thus, adjustable compliant actuators are being cautiously incorporated into new exoskeletons and active orthoses. Some simulation-based studies have evaluated the benefits of incorporating compliant joints into such devices. Another reason that compliant actuators are desirable is that spasticity and spasmodic movements are common among patients with motor deficiencies; compliant actuators could efficiently absorb these perturbations and improve joint control. In this paper, we provide an overview of the requirements that must be fulfilled by these actuators while evaluating the behavior of leg joints in the locomotion cycle. A brief review of existing compliant actuators is conducted, and our proposed variable stiffness actuator prototype is presented and evaluated. The actuator prototype is implemented in an exoskeleton knee joint operated by a state machine that exploits the dynamics of the leg, resulting in a reduction in actuation energy demand and better adaptability to disturbances. [ABSTRACT FROM PUBLISHER]

Abstract: Adaptable to nonstructural environment, compliant joints are competent candidates for flexure fingers in humanoid robotic hands. This paper presents an equivalent pin model (EPM), which provides an in-depth understanding on flexure finger dynamics by accounting for the moving rotation center and varying radius of a compliant joint. Distinguished from other lumped-parameter formulations based on constant-axis pin-joint approximation, the large deformation of a compliant joint is characterized by closed-form solutions obtained from a distributed Euler–Bernoulli (E–B) beam model. Modeling tolerance guidelines derived by comparing the E–B model against finite element analysis (FEA) without neglecting shear distortions are provided for designing dimensions of a compliant joint. Design evaluation is illustrated with a flexure finger consisting of three phalanxes by comparing the maximum stress among different configurations. The EPM reveals critical effects of rotational center-offset and varying radius on the dynamic response of a flexure finger, showing that the negligence of these effects yields an out-of-phase prediction in joint rotation. Although presented in the scope of finger manipulation, the method is expected to have potential applications for multi-body dynamics involving compliant mechanisms. [Copyright &y& Elsevier]

Highlights: [•] A novel, sensorized, elastomer coupling based on the principle of jaw couplings is presented. [•] The elastomer coupling is integrated into a self-contained, rotatory joint drive. [•] Integrated rotary position sensors measure the torsion angle of the coupling. [•] A system identification of the elastomer coupling is realized and models are derived. [•] Using these models with the torsion measurement the acting torque can be estimated. [Copyright &y& Elsevier]

Purpose – The purpose of this paper is to propose a new methodological framework within which a compliant robotic joint can be studied. Design/methodology/approach – A new method is presented for detecting the direction of the robotic joint rotation when subjected to an external collision force. Findings – The behaviour of the silicone rubber shows strong non-linearity, therefore, the sensor-elements cannot be used for accurate measurements. Originality/value – A new type of safe robotic mechanisms with an internal measuring system is proposed in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Passive compliant joints with springs and dampers ensure a smooth contact with the surroundings, especially if robots are in contact with humans, but the passive compliant joints cannot determine precisely the position of the members of the joint or direction of the collision force. In this paper was proposed the structure of a passive compliant robotic joint with conductive silicone rubber elements as internal embedded sensors. The sensors can operate as absorbers of excessive external collision force instead of springs and dampers and can be used for some measurements. Therefore, this joint presents one type of safe robotic mechanisms with an internally measuring system. The sensors were made by press-curing from carbon-black filled silicone rubber which is an electro active material. Various compression tests of the sensors were done. The main task of this study is to investigate the application of a control algorithm for detecting the direction of the robotic joint angular rotation when subjected to an external collision force. Soft computing methodology, adaptive neuro fuzzy inference strategy (ANFIS), was used for the controller development. The simulation results presented in this paper show the effectiveness of the developed method. [Copyright &y& Elsevier]

For tasks that require robot–environment interaction, stiffness control is important to ensure stable contact motion and collision safety. The variable stiffness approach has been used to address this type of control. We propose a hybrid variable stiffness actuator (HVSA), which is a variable stiffness unit design. The proposed HVSA is composed of a hybrid control module based on an adjustable moment-arm mechanism, and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness of a joint can be simultaneously controlled. The HVSA provides a wide range of joint stiffness due to the nonlinearity provided by the adjustable moment arm. Furthermore, the rigid mode, which behaves as a conventional stiff joint, can be implemented to improve positioning accuracy when a robot handles a heavy object. In this paper, the mechanical design features and related analysis are explained. We show that the HVSA can provide a wide range of stiffness and rapid responses according to changes in the stiffness of a joint under varying loads by experiments. The effectiveness of the rigid mode is verified by some experiments on position tracking under high-load conditions. [ABSTRACT FROM AUTHOR]

Abstract: Antagonistic Driven Compliant Joints (ADCJs) are object of great interest in current robotics research, representing one of the most widely applied solutions to develop human-like and safe joints for human-robot interaction. Providing the joint with “actively” adjustable hardware compliance, ADCJs have two distinctive features: (1) the joint is powered by two independent “actuation units” and (2) each actuation unit works as a non-linear elastic element with an adjustable resting position. This paper proposes a sensorless torque control strategy suitable for ADCJs actuated robots. This method is based on two steps: (1) off-line characterization of the elasticity of the actuation units, defined by the force–elongation curve and (2) online estimation of the force exerted by each actuation unit, through a direct measure of the joint angle, and of the “resting position” of each actuation unit. The proposed force estimation method can be used to develop two independent force controllers, which can be then combined to regulate the resulting joint torque, with no need of additional torque sensors. The performance of the proposed torque control was evaluated over the shoulder and the elbow ADCJs of the 2-link 2-DOFs planar robotic arm NEURARM. The method proved to work effectively, achieving good performances on the test platform, and represents a suitable alternative to state-of-the-art sensor-based torque controls. [Copyright &y& Elsevier]

This paper presents the methodology followed on the design of a multi-contact point haptic interface that uses a bio-inspired control approach and a novel actuation system. The combination of these components aims at creating a system that increases the operability of the target, and, at the same time, enables an intuitive and safe tele-operation of any complex robotic system of any given morphology. The novelty lies on the combination of a thoughtful kinematic structure driven by an active-compliant actuation system and a bio-inspired paradigm for its regulation. Due to the proposed actuation approach, the final system will achieve the condition of wearable system. On that final solution, each joint will be able to change its stiffness depending on the task to be executed, and on the anatomical features of each individual. Moreover, the system provides a variety of safety mechanisms at different levels to prevent causing any harm to the operator. In future, the system should allow the complete virtual immersion of the user within the working scenario. [ABSTRACT FROM AUTHOR]

This paper presents a human-oriented approach to design the mechanical architecture and the joint controller for a biped robot. Starting from the analysis of the human lower limbs, we figured out which features of the human legs are fundamental for a correct walking motion, and can be adopted in the mechanical design of a humanoid robot. We focus here on the knee, designed as a compliant human-like knee instead of a classical pin-joint, and on the foot, characterised by the mobility and lightness of the human foot. We implemented an elastic actuator, with a simple position control paradigm that sets the joint stiffness in real time, and developed the basic controller. Results in simulation are discussed. In our approach the robot gains in adaptability and energetic efficiency, which are the most challenging issues for a biped robot. [ABSTRACT FROM AUTHOR]

Active control of composite structures has primarily focused on vibration control and other small-scale deformations. For use in morphing aircraft structures, a composite ''smart joint" is proposed, employing both shape memory alloy and shape memory polymer to replace a conventional rotary actuator. This joint functions as a discrete member capable of both actuation and structural rigidity in user programmable states, with large-scale tip deflections on the order of 10-20% camber. A strain energy model is used to prescribe joint deflection in terms of thermally varying material properties across the thickness of the joint, allowing the designer of a morphing system to select electrical power input and element composition as based on deflection, response speed, and load capacity. This model discretizes the transformation into a multiple step shape change maneuver using the tri-phase process to determine deflection both when heated and when set into its cooled state. Comparison with a finite element model confirms thermodynamics analysis as well as deflection accurate within 2% of analytically predicted behavior. [ABSTRACT FROM AUTHOR]

In order to further improve the efficiency of flapping wings, inspired by bird flight, a new compliant joint structure is proposed, which is easy to manufacture. The joint has the capacity of passive bending, twisting and sweeping under the aerodynamic effect of the flapping wing. A multi-objective optimization program for the compliant joint is developed, which is combined with the measured joint load. The optimized compliant joint has the effect of asymmetric passive deformation in a flapping cycle. The model wings with compliant joints are studied in the windless flapping experiment, wind tunnel experiment and free flight test. The experimental results show that the model wings have a significant advantage of power consumption compared with the original wings, and also have an advantage in the aerodynamic performance at low flight velocity and low angle of attack. [ABSTRACT FROM AUTHOR]