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Industrial robots are widely used in the painting industry, such as automobile manufacturing and solid wood furniture industry. An important problem is how to improve the efficiency of robot programming, especially in the current furniture industry with multiple products, small batches and increasingly high demand for customization. In this work, we propose an outer loop adaptive control scheme, which allow users to realize the practical application of the zero-moment lead-through teaching method based on dynamic model without opening the inner torque control interface of robots. In order to accurately estimate the influence of joint friction, a friction model is established based on static, Coulomb and viscous friction characteristics, and the Sigmoid function is used to represent the transition between motion states. An identification method is used to quickly identify the dynamic parameters of the robot. The joint position/speed command of the robot’s inner joint servo loop is dynamically generated based on the user-designed adaptive control law. In addition, the zero-moment lead-through teaching scheme based on the dynamic model is applied to a spray-painting robot with closed control system. In order to verify our method, CMA GR630ST is used to conduct experiments. We identified the parameters of the dynamic model and carried out the zero-moment lead-through teaching experiment to track the target trajectory. The results show that the proposed method can realize the application of modern control methods in industrial robot with closed control systems, and achieve a preliminary exploration to improve the application scenarios of spray-painting robots.

This paper presents the design, analysis, and development of a novel four degrees of freedom (4-DOF) endoscopic robot with cable-driven multisegment flexible continuum mechanisms. The endoscopic robot is mainly composed of the passive positioning arm, cable-pulley system, and 3-DOF flexible continuum mechanism. The forward and inverse kinematics of the endoscopic robot are derived based on the constant curvature assumption, and its working space, flexibility, and preoperative incision determination method are analyzed as well. Based on the hardware structure of the robot system, a control strategy and a control software are developed, and the continuum mechanism is kinematically calibrated to carry out the trajectory planning experiment and simulated surgery experiment. The experimental results show that the calibrated constant curvature model can be used for the motion control of the continuum mechanism, and the 4-DOF endoscopic robot can meet the visual field requirements of minimally invasive surgery.

This paper demonstrates the mechanical design, analysis, and evaluation of a knee-ankle orthosis (KAO) for lower limb rehabilitation, including shape memory alloy (SMA) actuators and DC brushless motor actuators. First, the mechanical structure of the KAO is detailed, including the actuator system, transmission mechanism, monitoring device, and processing method of SMA actuators. Next, the dynamic model of SMA spring actuators in the phase transition process is established based on the thermal constitutive model of SMA. In addition, the dynamic output response of the knee joint under three working states is analyzed, and the rotation angle of SMA soft actuator during bending is described by pseudo rigid body model. Finally, the output of SMA actuator is preliminarily evaluated through experiments. The experimental results show that the maximum displacement of SMA spring actuator is 54.36 mm, the maximum restoring force during phase transformation is 4.14 N, and the maximum rotation angle of SMA soft actuator is 43.18 deg. The experimental results are consistent with the theoretical model.

This paper illustrates the design and testing of a lower limb exoskeleton for walking assistance. First, the biomechanics of the human knee and ankle joints during walking and the strategy of energy recycling and releasing are introduced. Next, the hardware design of the exoskeleton is described. The exoskeleton is primarily composed of a waist module, a knee module, and an ankle module. Two clutch mechanisms are designed for one-way motion transmission, and an energy storage spring is designed to store the energy recycled from the human knee motion. Additionally, the modeling of the human-exoskeleton system is presented. Finally, experiments are conducted to verify the effectiveness of the developed exoskeleton. The experimental results demonstrate that the exoskeleton has the potential to recycle the negative work from the wearer’s knee flexion during the late stance phase and knee extension during the swing phase to assist the wearer’s ankle plantarflexion during the stance phase. During a gait cycle, reductions of 11.6% and 15.6% of the average muscle activities of the gastrocnemius and soleus are observed, respectively. In addition, the peak gastrocnemius and soleus activities during the push-off stage are reduced by 16.9% and 42.6%, respectively.

Recent developments have demonstrated that the brake pedal simulator (BPS) is becoming an indispensable apparatus for the break-by-wire systems in future electric vehicles. Its main function is to provide the driver with a comfortable pedal feel to improve braking safety and comfort. This paper presents the development and control of an adjustable BPS, using a disk-type magnetorheological (MR) damper as the passive braking reaction generator to simulate the traditional pedal feel. A detailed description of the mechanical design of the MR damper-based BSP (MRDBBPS) is presented in this paper. Several basic performance experiments on the MRDBBPS prototype are conducted. A return-to-zero (RTZ) algorithm is proposed to avoid hysteresis and improve the repeatability of the pedal force. In addition, an RTZ algorithm-based real-time current-tracking controller (RTZRC) is designed in consideration of the response lag of the coil circuit. Finally, an experimental system is established by integrating the MRDBBPS prototype into a self-developed automotive MR braking test bench (AMRBTB), and several control and braking experiments are performed. This research proposes a RTZRC control algorithm which can significantly increase the tracking accuracy of the brake pedal characteristic curve, particularly at a high pedal velocity. Additionally, the designed MRDBBPS prototype can achieve an effective and favorable control of the AMRBTB with a good repeatability.

For patients who need lower-limb kinetism rehabilitation training, this paper proposes an effective data-driven approach seeking the design of 1-degree-of-freedom (DOF) six-bar rehab mechanism through gait prediction by body parameters. First, gait trajectories from 79 healthy volunteers are collected along with their body parameters. Then, the normalized gait samples are clustered and regressed into a limited number of representative trajectories with K-means algorithm, and the cluster index is recorded as the label for each trajectory. Next, a genetic-algorithm-optimized support vector machine method is adopted to establish a classifier for the trajectories, obtaining the correspondence between body parameters and cluster labels of gait trajectories. As a result, once a group of body parameters are input into the classifier, the suitable gait trajectory can be predicted for the specific patient. A GA-BFGS algorithm is developed for 1-DOF six-bar mechanism synthesis and a GUI design software is presented that shows how the data-driven design process is realized. The novelty of this paper is using clustering and prediction technique to accomplish the patient-mechanism matching, so that simple, low-priced 1-DOF mechanisms could be adopted for large number of various patients without expensive customized design for each individual. In the end, a gait rehab device design example is provided, and a prototype device driven by a constant speed motor is presented, which illustrates the feasibility of the proposed method.

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.

Soft actuators and microrobots that can move spontaneously and continuously without artificial energy supply and intervention have great potential in industrial, environmental, and military applications, but still remain a challenge. Here, a bioinspired MXene-based bimorph actuator with an asymmetric layered microstructure is reported, which can harness natural sunlight to achieve directional self-locomotion. We fabricate a freestanding MXene film with an increased and asymmetric layered microstructure through the graft of coupling agents into the MXene nanosheets. Owing to the excellent photothermal effect of MXene nanosheets, increased interlayer spacing favoring intercalation/deintercalation of water molecules and its caused reversible volume change, and the asymmetric microstructure, this film exhibits light-driven deformation with a macroscopic and fast response. Based on it, a soft bimorph actuator with ultrahigh response to solar energy is fabricated, showing natural sunlight-driven actuation with ultralarge amplitude and fast response (346° in 1 s). By utilizing continuous bending deformation of the bimorph actuator in response to the change of natural sunlight intensity and biomimetic design of an inchworm to rectify the repeated bending deformation, an inchwormlike soft robot is constructed, achieving directional self-locomotion without any artificial energy and control. Moreover, soft arms for lifting objects driven by natural sunlight and wearable smart ornaments that are combined with clothing and produce three-dimensional deformation under natural sunlight are also developed. These results provide a strategy for developing natural sunlight-driven soft actuators and reveal great application prospects of this photoactuator in sunlight-driven soft biomimetic robots, intelligent solar-energy-driven devices in space, and wearable clothing.

The efficiency and accuracy for parallel robot play a significant role in the industrial production process. In order to further improve the motion performance of parallel robot, this paper focuses on the study of mechanism design, dynamic modeling and error analysis of a cable-linkage serial-parallel palletizing robot (CSPR). Firstly, the CSPR is designed as a series-parallel hybrid mechanism driven by flexible cables, which can effectively reduce the inertia and improve the dynamic response. As is known that kinematic design optimization of compliant mechanisms requires accurate yet efficient mathematical models, the kinematics and dynamic models are established by the homogeneous coordinate transformation method and Lagrange equation. Based on the dynamic mathematical model of the robot, a variety of sensors are chosen to construct the hardware control system and the sliding mode variable structure control strategy is also designed based on motion errors. Then, the motion performance and load carrying capacity of the CSPR were analyzed and compared in different operating conditions respectively, and the results verify the validity and efficiency of the mechanism.

Cable-driven parallel robot (CDPR) is a type of high-performance robot that integrates cable-driven kinematic chains and parallel mechanism theory. It inherits the high dynamics and heavy load capacities of the parallel mechanism and significantly improves the workspace, cost and energy efficiency simultaneously. As a result, CDPRs have had irreplaceable roles in industrial and technological fields, such as astronomy, aerospace, logistics, simulators, and rehabilitation. CDPRs follow the cutting-edge trend of rigid-flexible fusion, reflect advanced lightweight design concepts, and have become a frontier topic in robotics research. This paper summarizes the kernel theories and developments of CDPRs, covering configuration design, cable-force distribution, workspace and stiffness, performance evaluation, optimization, and motion control. Kinematic modeling, workspace analysis, and cable-force solution are illustrated. Stiffness and dynamic modeling methods are discussed. To further promote the development, researchers should strengthen the investigation in configuration innovation, rapid calculation of workspace, performance evaluation, stiffness control, and rigid-flexible coupling dynamics. In addition, engineering problems such as cable materials, reliability design, and a unified control framework require attention.

To avoid impacts and vibrations during the processes of acceleration and deceleration while possessing flexible working ways for cable-suspended parallel robots (CSPRs), point-to-point trajectory planning demands an under-constrained cable-suspended parallel robot (UCPR) with variable angle and height cable mast as described in this paper. The end-effector of the UCPR with three cables can achieve three translational degrees of freedom (DOFs). The inverse kinematic and dynamic modeling of the UCPR considering the angle and height of cable mast are completed. The motion trajectory of the end-effector comprising six segments is given. The connection points of the trajectory segments (except for point P3 in theXdirection) are devised to have zero instantaneous velocities, which ensure that the acceleration has continuity and the planned acceleration curve achieves smooth transition. The trajectory is respectively planned using three algebraic methods, including fifth degree polynomial, cycloid trajectory, and double-S velocity curve. The results indicate that the trajectory planned by fifth degree polynomial method is much closer to the given trajectory of the end-effector. Numerical simulation and experiments are accomplished for the given trajectory based on fifth degree polynomial planning. At the points where the velocity suddenly changes, the length and tension variation curves of the planned and unplanned three cables are compared and analyzed. The OptiTrack motion capture system is adopted to track the end-effector of the UCPR during the experiment. The effectiveness and feasibility of fifth degree polynomial planning are validated.

Cable-driven parallel robots (CDPRs) are a kind of mechanism with large workspace, fast response, and low inertia. However, due to the existence of various sources of error, it is unavoidable to bring uncertain cable lengths and lead to pose errors of the end-effector. The inverse kinematic model of a CDPR for picking up medicines is established by considering radii of fixed pulleys. The influence of radii of fixed pulleys on errors of cable lengths is explored. Error transfer model of the CDPR is constructed, and uncertain sources of cable lengths are analyzed. Based on evidence theory and error transfer model, an evidence theory-based uncertainty analysis method (ETUAM) is presented. The structural performance function for kinematic response is derived based on the error transfer model. Belief and plausibility measures of joint focal elements under the given threshold are obtained. Kinematic error simulations show that errors of cable lengths become larger with the increase of radii of fixed pulleys. Compared with the vertex method and Monte Carlo method, numerical examples demonstrate the accuracy and efficiency of the ETUAM when it comes to the kinematic uncertainty analysis of the CDPR.

In this paper, a robotic ankle–foot orthosis (AFO) is developed for individuals with a paretic ankle, and an impedance-based assist-as-needed controller is designed for the robotic AFO to provide adaptive assistance. First, a description of the robotic AFO hardware design is presented. Next, the design of the finite state machine is introduced, followed by an introduction to the modeling of the robotic AFO. Additionally, the control of the robotic AFO is presented. An impedance-based high-level controller that is composed of an ankle impedance based torque generation controller and an impedance controller is designed for the high-level control. A compensated low-level controller that is composed of a braking controller and a proportional-derivative controller with a compensation part is designed for the low-level control. Finally, a pilot study with eight healthy participants is conducted, and the experimental results demonstrate that with the proposed control algorithm, the robotic AFO has the potential for ankle rehabilitation by providing adaptive assistance. In the assisted condition with a high level of assistance, reductions of 8% and 20.1% of the root mean square of the tibialis anterior and lateral soleus activities are observed, respectively.

An evidence-theory-based interval perturbation method (ETIPM) and an evidence-theory-based subinterval perturbation method (ETSPM) are presented for the kinematic uncertainty analysis of a dual cranes system (DCS) with epistemic uncertainty. A multiple evidence variable (MEV) model that consists of evidence variables with focal elements (FEs) and basic probability assignments (BPAs) is constructed. Based on the evidence theory, an evidence-based kinematic equilibrium equation with the MEV model is equivalently transformed to several interval equations. In the ETIPM, the bounds of the luffing angular vector (LAV) with respect to every joint FE are calculated by integrating the first-order Taylor series expansion and interval algorithm. The bounds of the expectation and variance of the LAV and corresponding BPAs are calculated by using the evidence-based uncertainty quantification (UQ) method. In the ETSPM, the subinterval perturbation method (SIPM) is introduced to decompose original FE into several small subintervals. By comparing results yielded by the ETIPM and ETSPM with those by the evidence theory-based Monte Carlo method (ETMCM), numerical examples show that the accuracy and computational time of the ETSPM are higher than those of the ETIPM, and the accuracy of the ETIPM and ETSPM can be significantly improved with the increase of the number of FEs and subintervals.

The increasing requirement of powering portable electronic devices can be potentially met by recycling the biomechanical energy generated during the human joint motion through a knee-ankle exoskeleton. In this paper, a knee-ankle exoskeleton is designed to recycle the negative work from the wearer’s knee extension and ankle dorsiflexion. The exoskeleton can convert the mechanical energy into electrical energy for energy harvesting and assist the knee flexion and ankle plantarflexion to reduce the wearer’s metabolic cost during walking. It is mainly composed of two torsion springs, two one-way transmission mechanisms, a gear train, and a generator. The torsion springs can store the elastic energy when the wearer’s ankle and knee joints do negative work and release it to assist walking when positive work is required. The one-way transmission mechanisms are employed to filter the knee flexion and ankle plantarflexion and to convert the knee extension and ankle dorsiflexion into the one-way rotation of the generator by symmetrically arranging the gear train. Finally, experiments are conducted to evaluate the performance of the developed knee-ankle exoskeleton. The experimental results indicate that the exoskeleton can generate an average electrical power of 0.49 W and a maximum instantaneous electrical power of 1.8 W at a walking speed of 5.5 km h−1 during a gait cycle, and reductions of 3.48% ± 0.33%, 9.50% ± 0.29%, and 4.54% ± 0.47% of the average muscle activities of the semitendinosus, soleus, and gastrocnemius during a gait cycle are observed, respectively.

This paper proposes a cable-driven parallel waist rehabilitation robot with two-level control algorithm to assist the patients with waist injuries to do some rehabilitation training. The uniqueness of the robot is that it can accurately implement the relative lateral bending, flexion, extension, and rotation of the waist on the premise of the safety. This is enabled by a mechanism design according to the motion characteristics of the human waist, and it can satisfy the need of different waist injury patients. The kinematics and dynamics of the robot are analyzed. In addition, a two-level controller is introduced to improve the accuracy of the rehabilitation training trajectory on the premise of the safety of patients and reduce the system calculation. The proportion-integration-differentiation (PID) algorithm is adopted to realize the position control in the low-level controller to ensure the accuracy of the robot. In the high-level controller, the fuzzy algorithm is used to adjust the parameters of the low-level controller according to the tension variation of cables, which ensures the patient safety and the stable operation of the robot. Finally, a prototype waist rehabilitation robot is developed for experimental calibration and performance testing. Results indicate that the designed robot system can achieve the waist rehabilitation training and the control algorithm can improve the system performance under the external disturbance.

The external force sensing ability of the end-effector plays a significant role in restricting the refine operation of a surgical robot. This paper proposes an external force self-sensing method based on the cable-tension disturbance observer for a four-degree-of-freedom (4-DoF) surgical robot end-effector, which is actuated by three backdrivable cable-driven series elastic actuators (BCDSEAs). First, the design of the surgical robot end-effector is introduced with the experimental prototype of a 1-DoF flexible finger joint. Second, four kinds of dynamic models of the flexible finger joint are established and experimentally identified. A joint angle estimator is proposed based on a simplified dynamic model. Then, a closed-loop motion control method for the flexible finger joint is proposed. Third, a driving cable-tension estimator is constructed as the benchmark for the cable-tension disturbance observer under free motion. Meanwhile, an external force self-sensing estimator is proposed based on the motion control strategy and the cable-tension disturbance observer. Finally, the experimental results of joint tracking control present a good performance. The compensation algorithm for the external force under free motion is studied to reduce the system error. The experimental results of the external force self-sensing show an overall estimation accuracy of 85.97% with a range of 0.10–2.00 N.

The number of patients with knee impairments caused by a stroke, spinal cord injury, post-polio, injury, osteoarthritis, or other related diseases is increasing worldwide. Robotic devices such as knee exoskeletons have been studied and adopted in gait rehabilitation, as they can provide effective gait training for the patients and release the physical therapists from the intensive labor required by the traditional physical therapy. In addition, knee exoskeletons can augment human performance in normal walking, loaded walking, and even running by enhancing the strength of the wearers’ knee joints. A systematic review of knee exoskeletons is presented in this paper. The biomechanics of the human knee joint is firstly presented. Then, the design concepts of knee exoskeletons, including the actuators and sensors, are provided, followed by the introduction of the corresponding control strategies. Finally, the limitations of the available devices and the research and development directions in the field of knee exoskeletons are discussed, thus providing useful information to the researchers developing knee exoskeletons that are suitable for practical applications.

Although additive manufacturing (AM) has been developed rapidly and become an absolutely necessary tool for reducing the cycle and cost of new product development, the mechanical structures of most 3D printers based on Fused Deposition Modeling (FDM) technology are still traditional serial or parallel mechanisms with rigid components. In this paper, a novel cable-driven parallel 3D printer (CDPP) is developed. Compared with the traditional rigid mechanisms, CDPP has the advantages of larger workspace, higher payload-to-weight ratio, easier modularity and reconfigurability. A cable-driven module with three translational degrees of freedom and a follow-up tensioning module with a spring are adopted for positioning. Firstly, the inverse kinematics of the CDPP is derived considering the cable length constraint. The inverse dynamics model of the CDPP is established based on the Newton–Euler equation and the kinematics. Secondly, the system stiffness of the CDPP and stiffness along three coordinate axes are derived, respectively. The system static stiffness with respect to the stiffness constant of the spring and the coordinates of the moving platform are obtained. Finally, the experiments are performed based on numerical simulation. The results of experiments without executing extrusion demonstrate the simulation results about the static stiffness. The feasibility of the CDPP is verified via the experiments while executing extrusion.

In this paper a novel design approach was proposed for determining the optimal winding parameters of composite pressure vessels based on non-geodesic trajectories. With the aid of the differential theory and winding principles, the non-geodesic trajectories were derived for various tangent points. The obtained non-geodesics for composite pressure vessels were simulated using MATLAB to verify the validity of the trajectory design. The influence of the number of the tangent points and the roving bandwidth on the non-geodesic winding patterns was evaluated. The optimal number of the tangent points and the roving bandwidth were then determined while ensuring fiber stability and full coverage on the mandrel . The finite element model of the pressure vessel was established, taken variable ply thicknesses and angles along the dome meridian into account. In addition, the stress distributions of the aluminum liner and the composite overwrap were obtained and the burst pressure of the pressure vessel was predicted. The specimen of a composite pressure vessel was fabricated using the filament winder and the experimental results were consistent with the theoretically predicted ones. It is concluded that the present method is of great significance for design and manufacture of composite pressure vessels.

This paper presents the development and feedback force control of a safe, lightweight, yet powerful, and stable passive force feedback data glove (FFDG), utilizing a disc-type magnetorheological (MR) brake as the force feedback device. Firstly, a detailed illustration of the mechanical design of the FFDG, including transmission structure, MR brake, and angle measuring mechanism, is presented. Then, to achieve a precise feedback force control, the design and modelling of a current controller based on the buck circuit are carried out. This is followed by the tracking control of the feedback force, using conventional PID and adaptive fuzzy-PID control schemes. The control effect of the two methods is evaluated and compared through simulations. Finally, an experimental set-up is established, and a series of experiments are carried out on both the manufactured MR brake and the FFDG prototype. The results verify the feasibility and stability of the developed FFDG, and demonstrate that the feedback force tracking accuracy of the adaptive fuzzy-PID controller is satisfactory.

Task-oriented modular design and safety monitoring are demonstrated to be outstanding challenges for robots in practical application. In order to obtain better flexibility and better obstacles avoidance capability, design and analysis of a modular cable-driven parallel robot (MCDPR) are presented in this paper, which can be reconfigured to several configurations in engineering applications by changing the number of the mobile modules and the connection mode of the end effector. With regard to the motion control and safety monitoring system, the design and implementation of hardware and software are presented. An experimental prototype for the MCDPR is developed, followed by a brief illustration of the connection mode between the end effector and cables, and the installation of monitoring nodes. The performance of the MCDPR is discussed experimentally, including real-time pose monitoring and obstacle avoidance. The results verify the feasibility and efficiency of kinematics model and obstacle avoidance method, and the results also indicate that the designed motion control and safety monitoring system can realize trajectory tracking control, real-time safety monitoring, and obstacle avoidance for the MCDPR.

Dynamic analysis is required for achieving higher efficiency of cable-driven parallel robots. This paper presents the dynamic analysis of the cable-driven parallel robots using the Lagrange’s method, taking cable’s mass and elasticity into account. The Lagrange’s equations of motion are derived and evaluated for the generalized coordinates of the system. The dynamic motion of the parallel robot is expressed by the generalized forces and generalized coordinates to completely specify the configuration of the whole mechanical system as well as every component of the system. The cables are modeled to control and design the motion of each part of the rigid body. The elasticity is determined using the optimal cable’s tensions and lengths. Numerical simulations are performed to obtain the dynamic motion of the cable-driven parallel robots and. Experimental analyses and the effect of the mass of the end-effector on the cable’s tension and elasticity are also investigated. These examples illustrate that the general motion of the rigid body is superior described in terms of a set of independent coordinates. The results indicate that a better speed of the end-effector can be achieved by adding the linear and rotational motions of the electrohydraulic cylinder actuators into the traditional cable-driven parallel robots.

Static response analysis of a dual crane system (DCS) is conducted using fuzzy parameters. The fuzzy static equilibrium equation is established and two fuzzy perturbation methods, including the compound function/fuzzy perturbation method (CFFPM) and modified compound function/fuzzy perturbation method (MCFFPM), are presented. The CFFPM uses the level-cut technique to transform the fuzzy static equilibrium equation into several interval equations with different cut levels. The interval Jacobian matrix, the first and second interval virtual work vectors, and the inverse of interval Jacobian matrix are approximated by the first-order Taylor series and Neumann series. The fuzzy static response field for every cut level is obtained by a synthesis of the compound function technique, the interval perturbation method, and the fuzzy algorithm. In the MCFFPM, the fuzzy static response field for every cut level is derived based on the surface rail generation method, the modified Sherman–Morrison–Woodbury (SMW) formula, and the fuzzy theory. Compared with the Monte Carlo method (MCM), numerical examples demonstrate that the MCFFPM has a better accuracy than the CFFPM and both of them bring a higher efficiency than the MCM, especially when it comes to effects of fuzzy parameters on uncertainty quantification (UQ) of the static response of the DCS.

Aiming at the structural characteristics and working methods of the cable-driven robot, an experimental platform oriented to the driving force control of cable was built. The platform has a double cable driven system, that is, one cable is driven by two motors and performs reciprocating motion. Because the cable system has strong non-linearity and is easily disturbed, a PID controller based on the principle of structural invariance is designed. The experimental platform master control PLC completes the data interaction with the monitoring program through the OPC server, and realizes the driving force control of the experimental platform through RS232 communication. Finally, program realizes the real-time monitoring of the platform status. The experimental results show that the driving force control of the cable is significantly success, the real-time performance and accuracy of the monitoring interface also achieve the expected results.

Paint film can protect and decorate the metallic workpieces. Automatic defect detection of paint film is important and challenging for intelligent manufacturing. In this paper, the surface quality of paint film is detected using defection system combining with deep learning. The image set of paint film is first collected for training and testing, which includes 2000 images. We use both SSD and Faster R-CNN methods to detect the defects of paint film. Finally, the framework of defect detection program is implemented through virtual instrument and python. Experiments indicate that the SSD and Faster R-CNN methods can get good experimental data in the paint film detection. As opposed to previous visual detection methods, the defect detection method using deep learning does not have to manually design defect characteristics previously, which is more robust. Moreover, the proposed framework can be easily applied to other industrial application fields, such as detection of wood defects, surface defect detection of parts and weld defect detection.

Soft actuators and microrobots that can move spontaneously and continuously without artificial energy supply and intervention have great potential in industrial, environmental, and military applications, but still remain a challenge. Here, a bioinspired MXene-based bimorph actuator with an asymmetric layered microstructure is reported, which can harness natural sunlight to achieve directional self-locomotion. We fabricate a freestanding MXene film with an increased and asymmetric layered microstructure through the graft of coupling agents into the MXene nanosheets. Owing to the excellent photothermal effect of MXene nanosheets, increased interlayer spacing favoring intercalation/deintercalation of water molecules and its caused reversible volume change, and the asymmetric microstructure, this film exhibits light-driven deformation with a macroscopic and fast response. Based on it, a soft bimorph actuator with ultrahigh response to solar energy is fabricated, showing natural sunlight-driven actuation with ultralarge amplitude and fast response (346° in 1 s). By utilizing continuous bending deformation of the bimorph actuator in response to the change of natural sunlight intensity and biomimetic design of an inchworm to rectify the repeated bending deformation, an inchwormlike soft robot is constructed, achieving directional self-locomotion without any artificial energy and control. Moreover, soft arms for lifting objects driven by natural sunlight and wearable smart ornaments that are combined with clothing and produce three-dimensional deformation under natural sunlight are also developed. These results provide a strategy for developing natural sunlight-driven soft actuators and reveal great application prospects of this photoactuator in sunlight-driven soft biomimetic robots, intelligent solar-energy-driven devices in space, and wearable clothing.

By introducing the subinterval perturbation method (SIPM), a hybrid compound function/subinterval perturbation method (HCFSPM) is presented for a dual-crane system (DCS) with large interval variables. The HCFSPM employs the SIPM to decompose a large interval variable into several subinterval variables with small uncertain levels. The interval kinematic compound function vectors and their inverses are approximated by the first-order Taylor and Neumann series, respectively. Based on the monotonic technique, the bounds of original luffing angle vectors are derived. Compared with the first-order compound function/interval perturbation method and the Monte Carlo method, numerical examples verify the effectiveness of the HCFSPM at conducting uncertain kinematic analysis of the DCS, especially when it comes to large uncertain levels.

This paper proposes a hybrid uncertainty analysis method (HUAM) based on the first-order interval perturbation method (FIPM) and Monte Carlo method (MCM) for minimum resultant force response analysis of the lower limb traction device (LLTD) of a hybrid-driven parallel waist rehabilitation robot (HDPWRR) with interval parameters. Based on the analysis of cable angles by using the interval algorithm, the problem of non-uniqueness of the force solution in redundant constraint mechanisms is solved. The force response domain prediction with interval parameters on rehabilitation patients is estimated by using the HUAM which combining the first-order interval perturbation technique with direct Monte Carlo method in different stages, and it reduces the calculation amount. First, the kinematic and static models of the LLTD with deterministic information are established according to its work principle. Then, the interval matrices with interval parameters are calculated by using the FIPM and the response of cable angles is combined with the static model. Third, by numerical examples, the accuracy and efficiency of the HUAM for solving the force response domain problem with interval parameters are verified. The bounds of cable angle response domain of the interval LLTD model are determined. Finally, the minimum resultant force response domain prediction with interval parameters on rehabilitation patients is estimated by combining the FIPM and MCM.

This paper illustrates the development and experimental validation of a robotic ankle–foot orthosis (AFO) with a series elastic actuator (SEA) and a magneto-rheological (MR) brake. First, the biomechanics of a human ankle joint during walking is explained. Next, the hardware design of the robotic AFO is introduced, including its mechanical structure, actuator design and configuration, and electronic system. The SEA is primarily composed of an electric motor, a planetary gearbox, a torsion spring, and a pair of bevel gears. The MR brake can modulate the viscosity of the robotic AFO and generate a large braking torque of 21.8 Nm with a low power of 8.8 W. Additionally, the modeling of the robotic AFO is presented, followed by an introduction to its control; several gait evaluation indices are proposed as well. Finally, a pilot study is conducted to verify the effectiveness of the developed robotic AFO. The experimental results demonstrate that the robotic AFO has the potential to provide dorsiflexion assistance, thus preventing foot slap and toe drag, in addition to plantarflexion assistance for the forward propulsion of the body. During a gait cycle, an average power of 0.23 W is harvested, and an 8% improvement in the system energy efficiency is achieved.

This paper presents a new trajectory planning method based on the improved quintic B-splines curves for a three degrees-of-freedom (3-DOF) cable-driven parallel robot (CDPR). First, the conditions of positive cables’ tension are expressed in terms of the position and acceleration constraints of the end-effector. Then, an improved B-spline curve is introduced, which is employed for generating a pick-and-place path by interpolating a set of given via-points. Meanwhile, by expressing the position and acceleration of the end-effector in terms of the first and second derivatives of the improved B-spline, the cable tension constraints are described in the form of B-spline parameters. According to the properties of the defined pick-and-place path, the proposed motion profile is dominated by two factors: the time taken for the end-effector to pass through all the via-points and the ratio between the nodes of B-spline. The two factors are determined through multi-objective optimization based on the efficiency coefficient method. Finally, experimental results on a 3-DOF CDPR show that the improved B-spline exhibits overall superior behavior in terms of velocity, acceleration, and cables force compared with the traditional B-spline. The validity of the proposed trajectory planning method is proved through the experiments.

Ultra-high fiber tension can provide sufficient compressive stresses to retain the permanet magnets mounted on the surface of the spindle. Therefore, a filament-wound sleeve with ultra-high fiber tension is designed to provide the radial compressive stress on the permanent magnet. Based on the elasticity theory, an approach for calculating the fiber stress distributions of composite layers and the radial compressive stresses on permanent magnets under different winding tensions are presented. The maximum winding tension of carbon fibers and the radial compressive stresses of composite layers are obtained by experiments. The fiber stresses of winding layers at the end of winding process under various winding tensions are calculated using the analytical method and finite element method, respectively. The results indicate that the analytical method can accurately predict the fiber stress distribution of the sleeve at the end of winding process and the radial compressive stresses on permanent magnets. The results obtained using the analytical method and the ones using the finite element method have a good agreement. The comparison between the analytical and experimental results is within the acceptable error. Therefore, filament-wound sleeves with ultra-high fiber tensions can satisfy the design requirements of high-speed permanent magnet rotors.

In this paper a carbon fiber reinforced composite cantilever cylinder under gravity was designed using the cantilever beam theory. The finite element model of the composite cantilever cylinder was established using software ANSYS. The static and dynamic bending responses of the cantilever cylinder were investigated with the aid of the finite element method and theory of flexible multi-body dynamics. The deflection calculated using fully constraints at the root of the cantilever cylinder under gravity satisfies the design requirements. Moreover, the response curves of deflections of the cantilever cylinder with time were obtained in terms of the step motion and sinusoidal motion, respectively, using software ADAMS. The deflections of the cantilever cylinder were also evaluated for various motions. The results indicate that the maximum deflections of the cantilever cylinder for the both motion modes do not exceed the allowable design values. The present models and methods are able to provide a useful reference for design and production of carbon fiber composite cantilever cylinders.

People with diseases such as stroke, spinal cord injury, and trauma usually have paretic ankle involvement because of the plantar flexor and dorsiflexor muscle weakness. Individuals with paretic ankle normally have the drop-foot gait, which has the complications of foot-slap after heel contact and toe-drag during the swing phase of a gait cycle. This could cause slow walking speed, short step-length, high metabolic cost, and high risk of tripping. Ankle-foot orthotic intervention is mostly prescribed to treat paretic ankle impairments. In addition, ankle-foot orthoses (AFOs) have been developed to assist human walking, which can reduce the wearer's metabolic cost of walking. To date, three kinds of AFOs have been developed, including the passive AFOs, semi-active AFOs, and active AFOs. This paper provides a systematic review on these three types of AFOs, where the biomechanics of normal and pathological gaits of human, the design concepts of the AFOs, and motion data collection of the human-machine system in human trials are described. The limitations of the currently developed AFOs and future research and development directions of AFOs are discussed, which would provide useful information for researchers to develop suitable AFOs.

Deterministic kinematic modeling and stochastic luffing angular response field prediction of the dual automobile cranes system (DACS) are studied in this paper. For the response analysis of the DACS with deterministic information, the inverse kinematics are analyzed. For the prediction of luffing angular response field of the DACS with narrowly random payload parameters, a narrowly random model is introduced. In the narrowly random model, the payload parameters with certain probability distribution are modeled as random variables. Based on the narrowly random model, the equilibrium equation of luffing angular response vector of the DACS with random parameters is derived. Then a perturbation-based random composite function method (PRCFM) is proposed. Based on the PRCFM, the first-order Neumann series expansion and the proposed random variable functional moment method, a modified hybrid random method (MHRM) for the luffing angular response field prediction of the DACS with narrowly random payload parameters is proposed. In the MHRM, the statistical characteristics of luffing angular response vector are determined. Numerical results show the feasibility and efficiency of the MHRM for solving the narrowly stochastic DACS problems compared with the Monte Carlo method. The effects of different random parameters (y, z, $$\theta $$ ) on the DACS luffing angular response field are also investigated deeply, and numerical results indicate the impact on the variances made by the randomness in the random payload parameter y is larger than those made by random payload parameters z and $$\theta $$ .

The binding effect of fiber materials due to the winding tension during the filament winding process of arch-shaped cross sections was successfully evaluated using the Finite Element Method (FEM). The use of FEM was validated by comparing results obtained with the results from the numerical analysis of a classic cylindrical mandrel winding model. In this study, four methods were combined in the commercial finite element code ANSYS to predict the change trend of the residual stress of the layer and explore the relationship between the winding layer thickness and the winding relaxation effect. These methods include the element birth and death option, which was used to simulate the step-by-step winding process, the thermal parameter method, which produced the equivalent filament winding tension, contact analysis, which was used to carry out the transmission of radial pressure and deformation, and the restart method, which was used to simulate the procuring process. Compared with the mathematical algorithm and test of variable thickness, the results of FEM were in the range of allowable error. Therefore, these results provide a useful reference in designing the filament wound composite structures with considerably high fiber tensions.

This paper presents the design and verification of a piezoelectric energy harvester with compound two-stage force amplification frame and compact footprint size to achieve high power output for a piezoelectric stack. An improved design of the conventional bridge-type force amplification frame is proposed with compound beam, which is able to maintain the large force amplification ratio while bearing a large loading force. Analytical model is developed based on Euler-Bernoulli beam theory to predict the force amplification ratio of the compound two-stage force amplifier. The architectural parameters are optimally tuned to achieve the largest force amplification ratio, so as to obtain the maximum power output for the piezoelectric stack under other constraints. Simulation study is carried out by finite element analysis to demonstrate the advantage of the proposed compound two-stage force amplifier over conventional design. Moreover, a prototype harvester is fabricated for experimental testing. Results indicate that the proposed harvester features high safety factor, large amplification ratio, and compact size, which can be adopted in practical application for scavenging energy induced by human footstep during walking.

Composite square tubes have gained increasing attention as energy absorbers due to their high specific energy absorption capacity and long stroke. One of the key important issues for producing filament-wound composite square tubes demands both windability and uniform coverage of winding patterns. Based on the analytic geometry, the spatial relation between the feed eye and the mandrel was outlined and the kinematic equations for coupling the motion of the mandrel and the feed eye were derived. Consequently, a design method for small-angle winding of composite square tubes was proposed, taking the non-slippage condition of winding trajectories into account. A periodically geodesic winding theory was presented and its winding error for various initial winding points was analyzed. The designed fiber patterns were then applied to the practical production of a composite square tube with small winding angles. The results show that the present design method for filament-wound square tubes is accurate and reliable. The obtained kinematic equations and motion laws of the feed eye and the mandrel satisfy the basic winding principle and manufacturability of filament-wound composite square tubes. The present method is able to provide a useful tool for design and production of composite square tubes.

An autotracking algorithm based on a hybrid grey prediction model is presented for autonomously navigating the laparoscopic visual window of a robot-assisted surgical system. This method can be applied to any view angle of the three-dimensional (3D) laparoscope with a 200 ms predictive motion. Firstly, a preset parameter-based tracking algorithm is proposed based on the kinematic relationships between instrument arms and laparoscope arm. Subsequently, a hybrid grey prediction model is constructed through the combination of the optimized GM(1,1) and grey Verhulst models with the use of an adaptive weight-tuning method and a filtered amendment method. Furthermore, the algorithm results in a constant distribution area ratio, whereby the instrument marks can be guaranteed to lie within the field of the visual window, such that the concurrent motion of the visual window and the instrument marks can be realized. The visual window can sustain automatic tracking of the movement of the marks. The user does not have to switch to the target controlling mode by adjusting the master-slave mapping. Finally, the proposed algorithm is verified through simulations with real motion trajectories from a Phantom Omni master manipulator. The results validate the correctness, feasibility, and robustness of this approach.

In this paper two winding methods were applied to produce filament-wound composite elbows, which are the whole application of non-geodesics, and the application of geodesics for the torus section and non-geodesics for cylindrical end sections. The resulting winding patterns were numerically simulated for various numbers of partitions. Tsai-Wu failure indices of the composite elbows obtained using various initial winding angles were calculated and the burst pressure of the elbow was predicted using finite element method. The results reveal that the whole application of non-geodesics leads to better structural performance of the composite elbows than the partial application of non-geodesics for cylindrical end sections. The present non-geodesics-based method provides a useful reference tool for design and production of filament-wound composite elbows.

Unbalance is an inevitable issue in rotating machineries due to the manufacturing tolerances, the assembly errors, the damage in rotating components, etc. The effects of unbalance on the nonlinear dynamics of cracked rotors are investigated in this paper. In order to overcome the assumption of weight dominance, 3D finite element models are employed to discretize the rotor and several contact pairs are defined on the cracked surfaces to simulate the intermittent breathing behavior of crack. Then, the complex free interface component mode synthesis method (CMS) is employed to reduce the model’s order and to increase the computational efficiency. Finally, the obtained models are used to study the effects of concentrated and distributed unbalances on the nonlinear dynamic response of cracked rotors. The results show that the unbalance can significantly affect the breathing mechanism of crack and consequently dramatically change the rotor’s dynamic behaviors. Moreover, the different levels and orientations of unbalance lead to obviously different results. Besides, the responses of rotors with two asymmetric distributed unbalance are similar to those of rotors with a single concentrated unbalance though the rotors are overall balanced.

This paper is related to the design, analysis and control of a winding hybrid-driven cable parallel manipulator (WHCPM). The WHCPM has the advantages of both cable parallel manipulator and hybrid-driven planar five-bar mechanism. Design of the WHCPM is explained, and the structure static analysis is carried out by using finite element method. Dynamics and payload capability of the WHCPM are studied. The WHCPM prototype is built for precision tracking experiments. To evaluate the manipulator design, the dynamic control compensation is performed on the basis of the conventional PID controller and the adaptive fuzzy sliding mode controller. The simulated and experimental results are reported and the tracking performance of the WHCPM is significantly improved by applying the proposed control technique in comparison with the performance when applying the conventional PID controller.

This paper develops a dynamics-based nonsingular interval model and proposes a first-order composite function interval perturbation method (FCFIPM) for luffing angular response field analysis of the dual automobile cranes system (DACS) with narrowly bounded uncertainty. By using the nonsingular interval model to describe a structure parameter with bounded uncertainty, the reasonable lower and upper bounds can be obtained, which is quite different from the traditional interval model with approximate bounds only from a large number of samples. Firstly, for the DACS with deterministic information, the inverse kinematics is analyzed, and the dynamic model of the DACS is established based on the virtual work principle and the inverse kinematics. Secondly, considering the nonsingularity of the dynamic response curves, a dynamics-based nonsingular interval model is introduced. Based on the nonsingular interval model, the interval luffing angular response vector equilibrium equation of the DACS is established. Thirdly, a first-order composite function interval perturbation method is proposed. In the FCFIPM, the composite function vectors are expanded by using the first-order Taylor series expansion, based on the differential property of composite function and monotonic analysis technique, the lower and upper bounds of the interval luffing angular response vector of the crane 1 and crane 2 of the DACS are determined. The first case is to investigate the deterministic kinematics and dynamics of the DACS with a given trajectory. The second case is provided to illustrate the detailed implementation process of constructing a dynamics-based nonsingular interval model. Finally, some numerical examples are given to verify the feasibility and efficiency of the FCFIPM for solving the luffing angular response field problem with narrowly interval parameters.