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The moving platform of the 4-SPS/CU (S is the spherical joint, P is the prismatic joint, C is the cylindrical joint, U is the universal joint) parallel mechanism is treated as a thin-plate element based on the absolute nodal coordinate formulation due to its physical characteristic. In order to eliminate high-frequency modes caused by the coupling between membrane and bending effects, the elastic mid-surface approach is used to evaluate the elastic force of the flexible moving platform. In order to formulate constraint equations between the flexible body and the rigid body, the tangent frame is introduced to define the joint coordinate system that is rigidly attached to the node at the joint, which is convenient for determining the constant vector in the joint coordinate system. The dynamics model of the parallel mechanism with the flexible moving platform is built based on the equation of motion. The simulation results show that the vibration frequency caused by the flexible body will be increased with the increasing stiffness of the material, and the kinematic trajectory and dynamics performance of the parallel mechanism are affected seriously when the smaller Young’s modulus is used, which illustrates that the effect of the flexible moving platform on the dynamic performance of the parallel mechanism should not be ignored.

The disk-shaft system is a power transmission system with several industrial applications. The shafts, depending on the mechanism application, can be connected by U-joints through different rotating axes. In spite of the many advantages, these joints transform a constant rotating speed into a variable output one. Therefore, the multi-body system is self-excited that lead to dynamic instability. Here, a driveline system including three elastic shafts, which carry three disks, is considered. The oscillating behavior and resonance phenomenon of this fluctuating mechanism are investigated qualitatively and quantitatively. The angle of joints, damping and stiffness effects are the major topics of the present contribution. Eventually, dynamic stability diagrams are obtained by using a reliable and exact method based on the Floquet theory. It can be found that variations of the first U-joint angle and the intermediate shaft characteristics have greater impact on the machine instability. It is revealed how the stability of the system can be achieved by changing the geometry, shaft damping and stiffness, which should be considered in design and practical applications.

A hyper-redundant space manipulator has extreme flexibility and is suitable to work in highly cluttered or multi-obstacles environment. However, its inverse kinematics is very challenging due to a large number of degrees of freedom (DOFs). In this paper, a modified modal method is proposed to solve the mission-oriented inverse kinematics. The spatial backbone of the manipulator is defined using a mode function, according to the mission requirement and working environment. All the universal joints are divided into M/2 groups, i.e. two adjacent universal joints comprise a group (M is the number of universal joints; it is assumed an even number. If it is an odd number, the remaining universal joint is a separated group). The whole manipulator is then segmented into M/2 sub-manipulators. Each sub-manipulator has 4-DOFs and is redundant for position or orientation. The last sub-manipulator is used to match the desired direction vector and the position of the end-effector with respect to the previous sub-manipulator's end. The remaining sub-manipulators are used to control the relative position between each other with one redundant degree of freedom. The equivalent link is fitted to the backbone function. The Cartesian coordinates of each node is then determined by combining the total length of the manipulator and the mode function. Then, the joint angles are solved through the position of each node. For each 4-DOF group, a parameter called arm angle is used to denote the redundancy and optimize its local configuration. Finally, typical cases of a 12-DOF and a 20-DOF manipulators are simulated. The results show that the method is very efficient for resolving the inverse kinematics of hyper-redundant space manipulators.

The present work deals with the optimization of universal joint using structural steel in order to reduce the mass and the stress value using FEM. The universal joint model was prepared in CAD software SOLIDWORKS and the static structural analysis was done in CAE tool ANSYS to determine the equivalent stress (von-mises). First of all, the failure analysis was done which shows that existing universal joint of structural steel was safe below the Torque moment 3850 N-m. Then the structural analysis of the universal joint was done for torque value 3800 N-m. The sensitivity analysis was run to determine sensitive area of universal joint where stresses were high and the sensitive dimensions were changed to find the minimum stress value and mass. For the optimized design, the Equivalent stress (von-mises) reduction in case of structural steel is 15.724% for the torque value of 3800 N-m. The mass of the universal joint reduces by 0.451%. The mass reduction from the cross alone is 4.473%. Final result shows that the stress reduction percentage and total mass reduction percentage comes out to be 15.7 and 0.451 % respectively.

This paper proposes the design of an electricity-powered lower-limb exoskeleton called “Human Universal Mobility Assistance (HUMA)”. HUMA was developed as a research platform with the objective of providing its wearer with weight-bearing assistance for human strength/endurance augmentation. It has 12 degrees of active/spring passive/free passive freedom to assist human locomotion. The artificial leg has two electricity-powered degrees of freedom (DoFs) for hip/knee flexions/extensions, passive spring-installed two DoFs for ankle inversion/eversion and plantarflexion/dorsiflexion, and two free, passive DoFs for hip roll/yaw movements. HUMA has mechanical structures for active artificial hip and knee joints; the hip actuator is not directly connected to the robot’s leg system, but a universal joint is installed between the actuator and the leg system to allow a free coaxial hip yaw/roll DoF for the wearer. Therefore, the hip-actuating torque is transferred solely for hip flexion/extension. Its active artificial knee is structured by a four bar-based polycentric linkage, and is power=driven by an actuator in the middle of the robot’s thigh segment through the other four bar-based power transmission linkage. This powered knee structure yields several advantages related to (1) human–robot knee alignment during leg motion, (2) the expansion of the zone of voluntary knee stability, (3) the angle-dependent variable knee torque/velocity amplification ratio, and (4) a reduction in the total moment of artificial leg inertia. The exoskeleton was tested for dynamic gait by using assistive torques determined by a control algorithm. Experiments were conducted on the robot while it walked at 5 km/h ( ≈ 1 . 39 m/s) with/without a 20 kg load, as well as for a 10-km/h ( ≈ 2 . 78 m/s) run.

Purpose Paediatric congenital esophageal atresia surgery typically requires delicate and dexterous operations in a narrow and confined workspace. This study aims to develop a novel robot assisted surgical system to address these challenges. Design/methodology/approach The proposed surgical robot consists of two symmetrical slave arms with nine degree of freedoms each. Each slave arm uses a rigid-dexterous configuration and consists of a coarse positioning manipulator and a distal fine operation manipulator. A small Selective Compliance Assembly Robot Arm (SCARA) mechanism was designed to form the main component of the coarse positioning unit, ensuring to endure large forces along the vertical direction and meet the operational demands. The fine positioning manipulator applied the novel design using flexible shafts and universal joints to achieve delicate operations while possessing a high rigidity. The corresponding kinematics has been derived and then was validated by a co-simulation that was performed based on the combined use of Adams and MATLAB with considering the real robot mass information. Experimental evaluations for the tip positioning accuracy and the ring transfer tasks have been performed. Findings The simulation was performed to verify the correctness of the derived inverse kinematics and demonstrated the robot’s flexibility. The experimental results illustrated that the end-effector can achieve a positioning accuracy within 1.5 mm in a confined 30 × 30 × 30 mm workspace. The ring transfer task demonstrated that the surgical robot is capable of providing a solution for dexterous tissue intervention in a narrow workspace for paediatric surgery. Originality/value A novel and compact surgical assist robot is developed to support delicate operations by using the dexterous slave arm. The slave arm consists of a SCARA mechanism to avoid experiencing overload in the vertical direction and a tool manipulator driven by flexible shafts and universal joints to provide high dexterity for operating in a narrow workspace.

This paper investigates the dynamic modeling and performance analysis of the 3-PRRU parallel manipulator; here, P, R and U denote the prismatic, revolute and universal joints, respectively. The studied 3-PRRU parallel manipulator possesses two rotational and one translational degrees of freedom without parasitic motion. For the dynamic modeling, the Newton–Euler formulation with generalized coordinates is employed to establish the system equations of motion for the 3-PRRU parallel manipulator. Then, the dynamic manipulability ellipsoid which provides a quantitative measure of the ability in manipulating the end-effector is adopted to evaluate the dynamic performance of the studied parallel manipulator. In order to demonstrate the feasibility of the proposed modeling and analysis method, numerical simulations are conducted on dynamic response and performance of the studied manipulator. A prototype is built up based on the proposed parallel manipulator. And the presented modeling method can serve the fundamentals for the optimization and control of the prototype in future work.

Purpose This paper aims to investigate the grease isothermal lubrication properties of the tripod sliding universal coupling (TSUC) in automotive transmission shaft and study its impact on a variety of factors to improve its grease lubrication properties. Design/methodology/approach Based on the simplified geometrical model, the research of grease lubrication properties of the TSUC was analyzed, and compared with oil lubrication in same parameters. Then the effects of effective radius, frequency (vehicle speed) and amplitude (angle between intermediate shaft and input shaft) on grease isothermal lubrication properties are theoretically investigated by using multigrid methods. Findings The results indicate that the grease isothermal elastohydrodynamic lubrication (EHL) film thickness shape and pressure distribution shape of the TSUC are similar to the oil lubrication, but the film thickness of grease lubrication is less than that of oil lubrication. Higher effective radius results in a wider pressure distribution, a lower center pressure and a thicker lubricating film. Higher frequency (vehicle speed) results in a remarkable second pressure peak and a thicker lubricating film. The effects of amplitude (angle between intermediate shaft and input shaft) and frequency have similar tendencies. Originality/value The numerical analysis research on grease lubrication properties of the TSUC is significant because the automotive transmission shaft is widely used. And it provides a new direction in designing TSUCs.

Maintenance for nuclear fusion vessel is crucial, yet it faces great difficulty due to the complex internal physical and geometric conditions. Since the limitation on inherent strength, load, size, etc, a manipulator robot can only complete very limited tasks. Robotic arm systems for remote operation such as JET and MPD can carry certain tools to complete a variety of operating tasks, but it is difficult to achieve the system which is very complex. Therefore, if the inherent idea of using a single robot to complete the specified functions can change, it is possible to make the problems simpler and easier to solve by adding auxiliary robots working together with the robotic arm systems to complete the assigned tasks. Under the above background, based on the deeply analyzing and refining the functional requirements of the vessel operation robot, proceeding from the perspective of ability to move and carry a certain operating device, this paper presents a wormlike creeping mobile robot walking on the V-shaped circular slot inside a nuclear fusion vessel such as EAST (Experimental Advanced Superconducting Tokamak). We have designed and implemented the principle prototype of the robot which has chain structure with n (n ≥2) creeping units. Each creeping unit is of three-part structure, which consists of fore segment, mid segment and back segment connected by bidirectional universal joint. The fore and back segments stretch the paws to contact the surface of V-shaped slot, while the mid segment realizes the overall movement of robot. In order to evaluate the design and implementation of the mobile robot platform, functional analysis is devoted to modules of robot. Especially for the requirements of walking stability on the V-shaped slot, creeping gait planning is analyzed to construct a multi-axis coordinating movement control scheme for creeping motion. Finally, by using the simulated EAST nuclear fusion vessel, the principle prototype is tested, and the preliminary evaluation of its functional index and related technical parameters is carried out. The experimental results show that the principle prototype of the robot can achieve stable walking on the V-shaped circular slot at the bottom of the nuclear fusion vessel, and it has a certain ability to carry equipments.

In this study, a drive system connected by rolling bearings and double universal joints is modeled as a closed-loop multibody system. Because of the existence of redundant constraints, the joint reaction forces cannot be determined uniquely through dynamic analysis. Based on the physical mechanism where the joint reaction forces are the resultants of contact forces at the joint definition point, a methodology of frictionless contact analysis is presented to identify joint reaction forces. In terms of D’Alembert’s principle, the dynamic equations of constrained multibody systems are equivalent to the equilibrium equations of all bodies composed of joint contact forces, externally applied forces, and inertial forces. The equivalent equilibrium equations provide a set of complementary equations to identify the contact positions and contact forces in the rolling bearings and double universal joints. The drive system is also simulated using ADAMS software, where all the joints are released and the corresponding constraint functions are replaced by the impact forces between the joint components. Some conclusions are obtained through the comparison of numerical examples between the proposed method and the ADAMS model. In the double universal joints, the equations are adequate and independent, which results in that the corresponding contact positions and contact forces can be solved uniquely. Then, the correlation between the data produced by these two models is acceptable in the engineering practices. Furthermore, contact details in the double universal joints can be obtained without the calculation of the relative motion between the cross-pin and yokes. However, the reaction forces in the rolling bearings are indeterminate due to that their complementary equations are not independent. The proposed method has high efficiency and acceptable precision.

The robotics, particularly the humanoid research field, needs new mechanisms to meet the criteria enforced by compliance, workspace requirements, motion profile characteristics and variable stiffness using lightweight but robust designs. The mechanism proposed herein is a solution to this problem by a parallel-series hybrid mechanism. The parallel term comes from two cable-driven plates supported by a compression spring in between. Furthermore, there is a two-part concentric shaft, passing through both plates connected by a universal joint. Because of the kinematic constraints of the universal joint, the mechanism can be considered as a serial chain. The mechanism has 4 degrees of freedom (DOF) which are pitch, roll, yaw motions and translational movement in z axis for stiffness adjustment. The kinematic model is obtained to define the workspace. The helical spring is analysed by using Castigliano's Theorem and the behaviour of bending and compression characteristics are presented which are validated by using finite element analysis (FEA). Hence, the dynamic model of the mechanism is derived depending on the spring reaction forces and moments. The motion experiments are performed to validate both kinematic and dynamic models. As a result, the proposed mechanism has a potential use in robotics especially in humanoid robot joints, considering the requirements of this robotic field.

In this paper, a new method called “projection kinematics” is presented for the determination of 3D configurations of DNA Origami Mechanisms (DOM) based on a single 2D projected image. The method enables finding all possible projected configurations of a DOM in space by solving the projection kinematics equations based on the minimum needed information measured from a 2D image. If redundant measurements are available, they can be exploited to eliminate ambiguous solutions. First, projection kinematic analyses were derived for the basic kinematic joints – revolute, prismatic, cylindrical and spherical joints and one degree-of-freedom (DOF) planar four-bar and two DOFs five-bar linkages. Then a generalized procedure for projection kinematic analysis is presented. Finally, a universal joint and a Bennett linkage fabricated by DNA origami self-assembly are chosen as proof-of-concept examples to verify the feasibility of projection kinematic analysis of DOM. This approach not only provides valuable guidance for the design of DOM, but also offers a low cost analysis approach for configuration estimation of spatial mechanisms when images from multiple viewing angles are not accessible, which is generally the case for the most commonly used analysis methods.

Friction stir welding (FSW) has been widely applied in many fields as an alternative to traditional fusion welding. Although serial robots can provide the orientation capability required to weld along curved surfaces, they cannot adequately support the huge axial downward forces that FSW generates. Available parallel mechanism architectures, particularly redundantly actuated architectures for FSW, are still very limited. In this paper, a redundantly actuated 2UPR-2RPU parallel robot for FSW is proposed, where U denotes a universal joint, R denotes a revolute joint and P denotes a prismatic pair. First, its semi-symmetric structure is described. Next, inverse kinematics analysis involving an analytical representation of rotational axes is implemented. Velocity analysis is also conducted, which leads to the formation of a Jacobian matrix. Sensitivity performance is evaluated utilizing level set and convex optimization methods, where the local sensitivity indices are unit consistent, coordinate free, and of definite physical significance. Furthermore, global and hierarchical sensitivity indices are proposed for the design process. Finally, dimension synthesis is conducted based on the sensitivity indices and the optimal link parameters of the parallel robot are obtained. In summary, this paper proposes a dimensional synthesis method for a redundantly actuated parallel robot for FSW based on sensitivity indices.

Methods for capturing wrist range of motion vary in complexity, cost, and sensitivity. Measures by manual goniometer, though an inexpensive modality, provide neither dynamic nor objective motion data. Conversely, optical motion capture systems are widely used in three-dimensional scientific motion capture studies but come with setup requirements and great cost. The electrogoniometer bridges the gap between portability and objective measurement. Previous studies have not evaluated the accuracy of an electrogoniometer in tracking the combined motions of in vivo human wrists. Our study aims to evaluate the accuracy of a 2 degree of freedom electrogoniometer using optical motion capture as the reference for in vivo wrist range of motion. First, a mechanical system constructed from two plastic pipes and a universal joint mimicked a human wrist to assess the inherent accuracy of the electrogoniometer without skin-motion artifact. Simulations of radial-ulnar deviation, flexion-extension and circumduction were evaluated. Second, six subjects performed three range of motion tasks of radial-ulnar deviation, flexion-extension, and circumduction for evaluation of the in vivo accuracy. Bland-Altman analysis quantified the accuracy. The mechanical experiment reported greater accuracy than the in vivo study with mean difference values less than ±1°. The in vivo accuracy varied across range of motion tasks, with mean differences greatest in the flexion-extension task (7.2°). Smaller mean differences values were reported in the radial-ulnar deviation task (−0.8°) and the circumduction task (1.2°). Accuracy requirements will vary depending on the research question. Task-based accuracy was reported during in vivo range of motion.

The purpose of this design project is to create transoral steerable devices with multibending using origami-inspired techniques for tracheostomy. The modular origami joint operator (MOJO) developed in this project is a bending mechanism that uses an origami universal joint as a hinge between modules of similar shapes and different lengths. It can achieve bending angles at specific locations through mechanical actuation forces from tendons or pneumatic pressure such that it can be navigated through the oral cavity and into the trachea without the need to extend the neck or use introducers. Moreover, modules of different lengths allow for customization so that more subjects are eligible to receive tracheostomy procedures. The first part of this report will analyze the current endotracheal tubes to review their benefits and shortcomings. Next, key performance targets and step-by-step procedures for operation devices will be listed. Following this, the proposed device, MOJO, will be compared with endotracheal tubes. The last section will present a brief discussion of safety and future developments.

There exist limitations to transoral robotic surgery in curvilinear navigation and tremor suppression. To address these challenges, this chapter introduces an adaptive and compliant transoral robotic surgery (ACTORS) with flexible manipulators and intelligent guidance. The patient-side manipulators are based on a flexible parallel mechanism with three sets of chains composed of superelastic nickel-titanium (Ni-Ti) rods and universal joints. Compared with conventional parallel mechanisms, this design optimizes the structure for adaptiveness and compliance by introducing superelastic structures. Due to adjoining to the head–neck–brain anatomical structures, transoral surgery raises a crucial demand for navigation accuracy. However, the transoral environment poses a prominent challenge because of the textureless surface, irregular shape, and nonrigid characteristics. Furthermore, it is notably tough for surgeons to determine the location of the endoscope instrument on account of the narrow field of view. For precise navigation during transoral surgical procedures, endoscopic simultaneous localization and mapping can provide real-time localization of the endoscope and the three-dimensional map of the surgical site, which can further be registered to preoperative imaging data to enhance visual understanding. This chapter elaborates on the ACTORS robot and the intelligent guidance in detail with a performance test and cadaveric trials.

We present a novel overactuated aerial vehicle based on four quadrotors connected to an airframe by means of passive universal joints. The proposed architecture allows to independently control the six degrees of freedom of the airframe without having fixed propellers at inefficient configurations or making use of dedicated rotor tilting actuators. After deriving the dynamic equations that describe its motion, we propose a linear control strategy that is able to successfully decouple rotation and translation, relying exclusively on on-board sensors. A prototype is built and preliminary experimental results demonstrate that the concept is feasible.Video: https://youtu.be/9ASP3FyhCJw. This research was supported by the ELKARTEK 2018 program of the Basque Government, grant agreement No. KK-2018/00082.

A cable-driven hyper-redundant manipulator is especially suited for manipulations in confined spaces. In most of the existing approaches, a controller is often designed to actuate the joints by pulling the corresponding cables without the feedback from remote sensors at the joints. The un-modeled elongations of these cables due to unknown tensions often cause a decrease in control precision. To improve the performance of such a manipulator, this paper presents an investigation where miniature potentiometers are integrated into the joints for angle feedback. Furthermore, a puller-follower controller is developed to control the three cables of a universal joint for not only closed- loop joint angle control but also cable tension preservation. Applying the Hooke’s Law, the cable tension is represented by its deformation. In this way, the controller is designed to realize both the desired angles and the cable deformations, without force sensing on the cables. Finally, experiments on a single joint and multiple joints were conducted to verify the effectiveness of this proposed controller.

This paper presents a three-degrees-of-freedom (DOF) gravity compensation mechanism for the waists of cooperative robots whose centers of mass change according to the arm poses. It comprises 2-DOF and 1-DOF gravity compensation mechanisms in series, and is capable of natural and agile motions such as bobbing and weaving. The 2-DOF mechanism for the upper part of the waist acts as a universal joint. To compensate for the gravity of this 2-DOF motion, a simple and robust link mechanism with one compressive spring is proposed. Moreover, for the complete gravity compensation regardless of the arm poses, a three-dimensional (3D) parallel link structure that maintains the upper body parallel to the ground is introduced. The 1-DOF gravity compensation mechanism, which provides the motions of the hip and thigh, also has a parallelogram structure to maintain the waist parallel to the ground. The implemented 3-DOF waist mechanism can compensate for up to 23 kg and its own weight. It has an adjusting mechanism that can easily calibrate the amount of compensation in case the weight of the upper body changes. The large workspace enables the upper body to move in any direction in a 3D space without singularity. Therefore, the robot with this waist can touch the ground to pick up objects on the ground as well as reach an object at a height of 2145 mm.

In the modern design of the transport vehicles drives—universal joints are frequently derived from the synchronous operation. In the paper were discussed ways to counteract this phenomenon. It is necessary to build a diagnozer for the evaluation of the changes in the rigidity of the supports, internal dumping, rigidity of components, etc. Method of diagnosis will allow an assessment of the spatial position of the shafts, their dynamics and as a result, adjust the phase of the shaft. Phase control in real-time will occur through the use of smart tools.

In this paper, a novel 3-UPU (P and U stand for prismatic and universal joints, respectively) parallel mechanism (PM) and its variant PM are proposed. Both of them have two rotational and one translational (2R1T) degrees of freedom (DOFs) without involving any parasitic motion. Mobility analysis shows that the three constraint forces provided by three limbs of the mechanism are located on the same plane and the mobile platform can translate perpendicular to this plane and rotate around any axis on it. Analysis of the mechanism’s motion characteristics demonstrates that the mobile platform outputs either pure rotation or pure translation. Moreover, the rotational axis can be fixed during the rotation process, which means no parasitic motion is involved. The causes of the motion characteristics are analyzed by the combination of an overall Jacobian matrix, a statistical method, and a geometric method. The PMs only need to translate or rotate once to move from the initial configuration to the final configuration, which allows for easy control of speeds. The relationship between mechanism parameters and singularity is analyzed. A speed control method for the PMs is proposed and a prototype is designed and made. Experiments are conducted to verify the determined motion characteristics, the speed control method, and the singularity analysis.

Nowadays, the elderly and the disabled are rapidly aging worldwide; therefore, the use of wheelchairs by the elderly and disabled continues to rise. However, many wheelchair users have difficulties adequately adjusting their sitting posture and often suffer from injurious falls, particularly, while traversing hilly roads or slowing down. In this study, a novel robotic seat is proposed to overcome these challenges, and numerical simulations are performed to verify its feasibility. The bottom of the seat is a spherical section, supported and driven by three omnidirectional wheels. An aluminum bar flanked with dumbbells is connected to the wheelchair through a universal joint as the test subject. The motion model is decoupled into two 2-D inverted pendulum models in the vertical plane and one rotation model in the horizontal plane. Two linear state feedback controllers based on the linear quadratic regulator method are used to stabilize the test subject in the vertical plane. The simulation results demonstrate the feasibility of the proposed robotic seat.

The bacterial flagellum is a motility organelle consisting of a rotary motor and a long helical filament as a propeller. The flagellar hook is a flexible universal joint that transmits motor torque to the filament in its various orientations that change dynamically between swimming and tumbling of the cell upon switching the motor rotation for chemotaxis. Although the structures of the hook and hook protein FlgE from different bacterial species have been studied, the structure of Salmonella hook, which has been studied most over the years, has not been solved at a high enough resolution to allow building an atomic model of entire FlgE for understanding the mechanisms of self-assembly, stability and the universal joint function. Here we report the structure of Salmonella polyhook at 4.1 &Aring, resolution by electron cryomicroscopy and helical image analysis. The density map clearly revealed folding of the entire FlgE chain forming the three domains D0, D1 and D2 and allowed us to build an atomic model. The model includes domain Dc with a long &beta, hairpin structure that connects domains D0 and D1 and contributes to the structural stability of the hook while allowing the flexible bending of the hook as a molecular universal joint.

This paper presents the mechanical design and prototyping of a reconfigurable universal joint. An electronically actuated mechanical switch allows to change joint’s configuration so that two different universal pairs can be obtained. One of the two revolute axes rotates freely whereas the other is driven by a servomotor: its direction can be chosen by the user, providing two different mechanical arrangements. It can be demonstrated that the use of this reconfigurable joint in a specific parallel kinematic manipulator equipped with three identical legs allows to change the mobility of its moving platform. The design proposed in the current work has been driven by analytical analyses and multibody simulations. A finite element analysis demonstrates the effectiveness of the mechanical design.

Piping inspection robots are of greater interests in industries such as nuclear, chemical and sewage. The design of such robots is highly challenging owing to factors such as locomotion inside pipes with varying diameters, cable management, and complex pipe bends (or) junctions. A rigid bio-inspired caterpillar type piping inspection robot was developed at LS2N, France. By introducing tensegrity mechanisms and four-bar wheel mechanisms, the design of this robot is modified into a reconfigurable system. The tensegrity mechanism employs a passive universal joint with three tension springs and three cables for actuation. The positioning of the end effector with respect to the base of the mechanism plays an important role in determining the maximum tilt angle (or) bending limit of the system. By workspace analysis of three case studies, the best solution is chosen which generates the maximum tilt. A static force analysis is then performed on the mechanism to determine its stability under the influences of preload. By the modification of design parameters, stable configurations are determined followed by which cable actuation of mechanism is analyzed for estimating applied forces.

This paper deals with the reconfiguration analysis of a 3-DOF (degrees-of-freedom) parallel manipulator (PM) which belongs to the cylindrical parallel mechanisms family. The PM is composed of a base and a moving platform shaped as equilateral triangles connected by three serial kinematic chains (legs). Two legs are composed of two universal (U) joints connected by a prismatic (P) joint. The third leg is composed of a revolute (R) joint connected to the base, a prismatic joint and universal joint in sequence. A set of constraint equations of the 1-RPU&minus, 2-UPU PM is derived and solved in terms of the Euler parameter quaternion (a.k.a. Euler-Rodrigues quaternion) representing the orientation of the moving platform and of the Cartesian coordinates of the reference point on the moving platform. It is found that the PM may undergo either the 3-DOF PPR or the 3-DOF planar operation mode only when the base and the moving platform are identical. The transition configuration between the operation modes is also identified.

This paper presents the development of a new robotic tail based on a novel cable-driven universal joint mechanism. The novel joint mechanism is synthesized by geometric reasoning to achieve the desired cable length invariance property, wherein the mechanism maintains a constant length for the driving cables under universal rotation. This feature is preferable because it allows for the bidirectional pulling of the cables which reduces the requisite number of actuators. After obtaining this new joint mechanism, a serpentine robotic tail with fewer actuators, simpler controls, and a more robust structure is designed and integrated. The new tail includes two independent macro segments (2 degrees of freedom each) to generate more complex shapes (4 degrees of freedom total), which helps with improving the dexterity and versatility of the robot. In addition, the pitch bending and yaw bending of the tail are decoupled due to the perpendicular joint axes. The kinematic modeling, dynamic modeling, and workspace analysis are then explained for the new robotic tail. Three experiments focusing on statics, dynamics, and dexterity are conducted to validate the mechanism and evaluate the new robotic tail's performance.

This paper proposes a dynamic modeling and performance analysis method of a novel 2-PUR-PSR parallel manipulator with parasitic motion, and P, U, S, R represent the prismatic joint, universal joint, spherical joint, and revolute joint, respectively. The explicit inverse dynamic equation of the parallel manipulator is derived by using Lagrangian formulation. The dynamic manipulability ellipsoid is introduced and divided into rotational and translational dynamic performance index to evaluate the dynamic performance of the parallel manipulator. In order to testify the feasibility of the proposed method, numerical simulations of the parallel manipulator with the given trajectory and workspace is conducted. Then, the actuation forces and the distribution of dynamic index are obtained.

SUMMARYThis paper introduces a novel kinematic of a four degrees of freedom (DoFs) device based on Delta architecture. This new device is expected to be used as a haptic device for tele-operation applications. The challenging task was to obtain orientation DoFs from the Delta structure. A fourth leg is added to the Delta structure to convert translations into rotations and to provide translation of the handle. The fourth leg is linked to the base and to the moving platform by two universal joints. The architecture as well as the kinematic model of the new structure, called 4haptic, are presented. Comparisons in terms of kinematic behavior between the 4haptic device and the existing device developed based on spherical parallel manipulator architecture are presented. The results prove the improved behavior of the 4haptic device offering a singularity-free useful workspace, which makes it a suitable candidate to tele-operated system for Minimally Invasive Surgery. The dimensions of the 4haptic device, having the smallest workspace containing a prespecified region in space, are identified based on an optimal dimensional synthesis method.

Parallel robots are defined as mechanisms with at least two independent links which connected a fixed platform to a final effector. This configuration has the advantage of distributing the loads applied to the final effector, providing greater rigidity, high accelerations and precision. However, it is a closed kinematic chain, with a work space limited by the restrictions introduced by its configuration. But despite its disadvantage in terms of workspace, it has comparative advantages with respect to serial robots make it the focus of study for multidirectional printing mechanisms. Therefore, in this work It calculated the direct, kinematic model of a platform with 6 degrees of freedom type RUS and differential kinematic control.

The design of multi-universal-joint drive shaft is essential for alleviating vehicle vibration. This paper proposes a novel and practical optimization method to reduce the vibration caused by multi-universal-joint drive shaft. Specifically, a dynamic model of a powertrain system including engine, shafts and universal joints is built in MATLAB which is an inalienable part of the fitness function when optimizing. Further, based on the model above, Genetic Algorithm (G.A.) is applied to optimize the drive shaft’s parameters: spatial positions and phase angles of universal joints and thickness of shafts’ shells. In each iteration of the G.A., the model is simulated under critical condition which is found by a field test of an experimental vehicle. What’s more, to verify the effectiveness of the optimization method, results from G.A. is adopted in a full-vehicle model built in ADAMS, indicating that the peak of torsional vibration is reduced greatly.

International audience; The application of robots for the inspection of pipelines are of greater significance in industries such as nuclear, chemical and sewage. The major problem in the design of these robots lies in the selection of a suitable locomotion principle, selection of an articulation unit that facilitates the robot to pass through pipe bends and management of cables. In this context, the design of a new bio-inspired piping inspection robot that resembles an elephant trunk has been presented. With the help of leg mechanisms and actuators, a caterpillar locomotion is used within this trunk for establishing adaptive contact points with the walls of pipeline. For the passage through bends and junctions, several case studies of existing researches have been taken into account for the design of an articulation unit. Two solutions, (i) a passive tensegrity structure and (ii) an active tensegrity structure have been proposed for the robot to pass through pipe bends and junctions. A detailed design analysis of the passive solution that uses a universal joint has been presented in this article.

Articulated tower is a compliant offshore structure deployed in deep waters for oil and gas exploration. The base of the tower is connected to the sea bed through universal joint, which allows the tower to rotate about horizontal axis (pitch). Articulated towers attain stability due to large buoyancy forces acting on it. Under extreme wave loads, the response of ALP can exceed the design limit causing discomfort to the occupants and create unfavourable working conditions. Structural control systems can be implemented in order to reduce the response of ALP, thereby protecting the structure from damages and to increase its life span. In this paper, a semi-active optimal control strategy using Magneto-Rheological damper is adopted to reduce the responses of ALP. Bouc-Wen model is used to describe the force generated by MR-Damper. For achieving the optimal performance of the control system, the applied voltage is varied according to the measured feedback at any moment to change the damping force using linear quadratic regulator technique. Several parametric studies have been conducted and the performance of the controller is evaluated. It is observed that the response of ALP is reduced considerably by using MR-damper as a semi-active control device. However, the capacity of the damper required for achieving the desired control is huge.

In order to achieve the mobile processing of large structural components or the remote maintenance of large-scale equipment, a compact and portable parallel machining robot named DiaRoM is designed and developed. According to the required degrees of freedom (DoFs), a parallel mechanism with the configuration of 4SPU-SPR (S, spherical joint; P, prismatic joint; U, universal joint; R, revolute joint) is proposed by using the type synthesis method based on Grassmann Line Geometry and Line-graphs. The kinematic optimization, driving system parameter optimization (DSPO) and prototype development for the robot are presented. The DiaRoM prototype can converse between horizontal and vertical working modes and realize flexible 5-axis machining.

Recent advancements in powered lower limb prostheses have appeased several difficulties faced by lower limb amputees by using a series-elastic actuator (SEA) to provide powered sagittal plane flexion. Unfortunately, these devices are currently unable to provide both powered sagittal plane flexion and two degrees of freedom (2-DOF) at the ankle, removing the ankle’s capacity to invert/evert, thus severely limiting terrain adaption capabilities and user comfort. The developed 2-DOF ankle system in this paper allows both powered flexion in the sagittal plane and passive rotation in the frontal plane; an SEA emulates the biomechanics of the gastrocnemius and Achilles tendon for flexion while a novel universal-joint system provides the 2-DOF. Several studies were undertaken to thoroughly characterize the capabilities of the device. Under both level- and sloped-ground conditions, ankle torque and kinematic data were obtained by using force-plates and a motion capture system. The device was found to be fully capable of providing powered sagittal plane motion and torque very close to that of a biological ankle while simultaneously being able to adapt to sloped terrain by undergoing frontal plane motion, thus providing 2-DOF at the ankle. These findings demonstrate that the device presented in this paper poses radical improvements to powered prosthetic ankle-foot device (PAFD) design.

This paper presents a year-long research after the aviation accident, which happened in the Czech Armed Forces. During this accident, the helicopter Mi-171 was severely damaged. This paper contains an analysis of the material and geometric properties of the part of the helicopter’s Mi-171 main gear, which failed during landing. The main gear contains a horizontal front strut, which is mounted to the fuselage via a coupling element in form of a cardan joint. The failure of this joint was ultimately responsible for the accident. This paper compares the qualitative properties of the joint manufactured by the Czech manufacturer and a former Soviet Union one.

This paper deals with a new universal coupling converter, which has been realized in form of a laboratory sample at Department of Electronics, FEECS. The circumstances of demand of a new coupling solution are presented firstly, descriptions of new concept and its function follows. Finally, the results obtained from the realized model are stated.

Two rotations and one translation (2R1T) parallel kinematic machines (PKMs) are suitable for the machining of complex curved surfaces, which requires high speed and precision. To further improve rigidity, precision, and avoid singularity, actuation redundancy, and overconstrained PKMs with fixed actuators and limited-degrees of freedom (DOF) limbs are preferred. However, there are few 2R1T PKMs with these features. This paper introduces a new 2R1T overconstrained PKM with actuation redundancy, which is called Tex4. The Tex4 PKM consists of four limited-DOF limbs; that is, two PUR limbs and two 2PRU limbs (where P denotes an actuated prismatic joint, U denotes a universal joint, and R denotes a revolute joint). The kinematic model of the proposed 2PUR-2PRU machine is presented along with the results of mobility, inverse kinematics, and velocity analysis. By considering the motion/force transmissibility, the dimensional parameters of the Tex4 PKM were optimized to obtain an improved satisfactory transmission workspace without singular configurations. Finally, a prototype based on the optimized parameters was fabricated, and its feasibility and accuracy were validated by motion and position error experiments. The Tex4 PKM has the advantages of high rigidity, simple kinematic model, and zero singularity in the workspace, which suggests that it has potential for use in the high-speed machining of curved surfaces.

Every palm oil plantation has different characteristics. In Indonesia, some of the palm oil plantations are unique because of its peaty, muddy, and bumpy features. Today, the existing Fresh Fruit Bunch (FFB) transport equipment is rigid and unable to follow the contour of outline of plantation ground, which limits its mobility. Therefore, it is necessary to design FFB transport equipment that offers ease of mobility. The new design has a universal joint feature that connects the front of part of the equipment (driver section) with the load carrier part (rear part). The design includes three-dimensional images with its simulations, two-dimensional images and the strength analysis of the joint. Both design drawings and strength analysis are carried out using SolidWorks engineering software. The result is a design of a universal joint with a dimension of 0.2 m in length and 0.15 m in width, and is capable of rotating in two directions; each at 30 degree on Y axis and 16 degree on X axis. All components of the universal joint are SS400 steel which has a tensile strength of 250 MPa. Calculation of strength with a tensile load of 1 ton results in a safety factor of 833. This safety factor ensures the maximum life span and strength of the universal joint.

Considering the large quantity of passengers in a running rail vehicle, its safety must be paid special attention to, which relies on the reliability of every critical component. Spherical universal joint is widely used in the suspension device of the gearbox in the transmission of railway vehicles for its functions of damping and cushioning. Since it’s commonly made of rubbers rather than the familiar metallic materials, its degradation behaviors and failure mechanisms have not been systematically investigated. In this study, multiple rubber spherical universal joints used in the urban rail transit train were found cracked and sticky during maintenance. Its design lifetime was 5 years, but this kind of failure occurred in

The dredger operation extended from protected water to harsher environments in recent years. This resulted in a change in design strategy. Understanding these complex dynamic interaction during the dredging operation using a Cutter Suction Dredger (CSD) can improve the production by reducing the downtime. CSD consists of the dredge hull, spud and the cutter shaft. A hybrid scaled model of the CSD is developed using Froude and Cauchy scaling for the different section of the CSD. The assembly was modelled in two sections. The spud hull assembly dynamics was modelled using WAMIT and ANSYS. The system was identified and reduced to a SDOF in the surge direction. The surge dynamics was coupled to the cutter shaft assembly using a roller support. Wave excitation acting on the assembly was determined using statistically linearised Morison equation. The assembly was linearised in frequency domain and transformed to state space and the temporal response was determined. A parametric study was carried out to understand the influence of the relative shaft dimensions and the coupling strength on the vibration transmission when subjected to an impulsive load. The results from the study indicated that shaft dimension asymmetry and coupling strength influences the vibration transmission.

The dynamics of a system comprising a heavy rotor which is coupled to a motor through a long and torsionally flexible drive shaft with universal joints (U-joints) at its both ends is studied numerically. The U-joints are arranged in Z-configuration to minimize the speed fluctuations between the input and output shafts. It is shown that for large parallel offset between the input and output shafts, Sommerfeld effect characterized by resonance capture and escape through resonance occur. The escape through resonance is associated with sharp jump in speed and reduction in torsional vibration amplitude. In fact, such jump phenomena occur at two different speed ranges, one near the natural frequency of the straight line arrangement of the U-joints and the other at half of that natural frequency. The nature of the dynamic response is affected by the rate at which the input shaft torque or power is varied.