This paper investigates the tribological and mechanical properties of silk-based nanocomposite coatings which are finding applications in optics, biomedicine and dentistry, thanks to the exceptional mechanical/optical properties and associated biocompatibility of silk. Three different nanocomposite formulations were synthesized, and thin films were prepared by spin coating at different thicknesses and with different post-deposition annealing processes. Ellipsometry, FTIR spectroscopy, AFM, nanoindentation, scratch testing, continuous/reciprocating wear testing, confocal microscopy and SEM were used to characterize the coatings. The results reveal that their hardness and elastic modulus are in the range 0.56–1.30 GPa and 23.6–55.4 GPa, respectively, which are much higher than those reported for other silk films in literature. Incorporation of titanate nanosheets also improved coatings’ scratch resistance.

To investigate the scratch behavior of short glass fiber (SGF) reinforced polybutylene terephthalate (PBT) composites, the scratch tests with the progressively increasing normal load were conducted for PBT reinforced with 0 wt%, 10 wt%, 20 wt% and 30 wt% SGF. The effect of fiber content and orientation on the scratch behavior of PBT composites and underlying scratch damage mechanisms were investigated. The addition of SGF alters the critical normal loads of onset fish-scale deformation and material removal respectively. The glass fiber fracture was observed and its damage mechanism was analyzed. The results show that although the bulk mechanical properties of PBT are enhanced, the addition of glass fiber generally causes poor scratch resistance. The guidance for designing scratch-resistant SGF reinforced PBT is also discussed.

The aim of this study is to analyze the stiffness of finite line contact under elastohydrodynamic lubrication (EHL) with linear and nonlinear force approximations. The numerical solution of the finite line contact is compared with experimental results of optical interferometry. Four types of profiles are evaluated: non-profiled roller, crowned roller, dub-off profile and logarithmic profile. For each type of roller, the geometry values vary in order to identify the behavior of the reduced contact force parameters. The results of the force model showed good correspondence with the numerical solution of the EHL contact.

The tribological behaviors of the high-performance Cu36Zr48Ag8Al8 bulk metallic glass (BMG) under dry-sliding, deionized water and NaOH solution conditions were systematically investigated and the corresponding wear mechanisms were revealed via analyzing the chemical composition and topography of wear track. The results illustrate that the Cu36Zr48Ag8Al8 BMG exhibits tribological properties superior to those of 316 stainless steel under different friction conditions, especially in a NaOH solution. During friction sliding, the formation of uniform and continuous metal-oxide layers on the surface can enhance its wear resistance and protect it from further corrosion by OH−. Furthermore, the NaOH solution and the dissolved products on the frictional surface form fluid-lubricating films, which may also reduce the friction coefficient and wear rate of the material.

B-doped TiO2 coatings with different B:Ti molar ratios were produced on Ti6Al4V alloy by a sol-gel dip-coating in order to improve tribological and electrochemical properties of Ti6Al4V. The properties of films were evaluated by XRD, XPS, SEM, surface tension-meter, tribotester and EIS. The highest roughness and hardness were obtained from B:Ti molar ratio of 2:1 TiO2 thin-film. TiO2 and B-doped TiO2 improved the wear resistance. While the mean CoF of Ti6Al4V was 0.39, TiO2 films reduced CoF significantly. B-doped TiO2 showed higher wear resistance than substrate and TiO2-film. Corrosion resistance was enhanced by TiO2 and the increasing B molar ratio provided improvement. The surface state changed after coatings. While TiO2 film showed hydrophobic behavior, B-doped all films exhibited hydrophilic characteristics.

Infrared microscopy is used to obtain through-thickness oil temperature measurements from EHL contacts between different surface materials (steel, silicon nitride and zirconia) for the lubricants Santotrac 50 and PAO4. The measurement technique was first adapted to overcome focussing issues due to the partially transparent zirconia surface. Results were used to infer in-contact rheological behaviour of the lubricants. Santotrac 50 shows significant shear localisation under all conditions with the position of the shear heating zone being highly affected by the contact surfaces' thermal properties. For PAO4, the shear profile depends on the contact surfaces’ thermal properties with moderate to high surface conductivities favouring uniform shearing, whereas highly insulating surfaces (zirconia) cause shear localisation at the surface for both lubricants. These results are used to interpret friction measurements and show how the thermal properties of surfaces can be used to control rheology and friction. This paper is prefaced by a review of thermal EHL theory upon which our analysis is based.

In the study we propose and examine a novel concept, eMR-TMD as we call it, replacing a standard tuned mass damper (TMD) by an electrical harmonic oscillator (RLC circuit). The concept employs an electromagnetic energy harvester (EEH) to extract energy from vibrations, an RLC circuit in which serial resonance phenomenon occurs and a magnetorheological (MR) damper. The approach does not require modifications to the structural part of the system, i.e. no additional mass and spring are needed. The essence of the concept relies on the introduction of a tuned RLC circuit between the EEH coil and the control coil of the MR damper. The RLC circuit parameters we select in such a way so that the electrical resonance frequency is close to or equal mechanical resonance frequency in which the eMR-TMD concept is applicable. Moreover, it is required that the RLC circuit's quality factor is greater than 1 and then the voltage activated the MR damper is higher than the EEH induced voltage at the resonance frequency. Fulfilling the criteria allows tuning the current in the MR damper's control coil so that it is maximized at resonance frequency and minimized at high excitation frequencies. To prove the concept's potential we test the engineered eMR-TMD system experimentally under sinusoidal excitations. We compare the obtained test results with those acquired with the MR damper powered directly from the EEH (dMR-EEH concept) and when the MR damper's control coil is not powered (without TMD concept).

This paper presents the design and implementation of a Tactile/Force sensor which has been used on a 3-DOF decoupled parallel mechanism for Human-Robot Interaction purposes.The sensor, called HexaTactile, is a soft tactile sensor array based on six MEMS barometers, where each of them is covered by a silicone layer in the form of an incomplete pyramid. HexaTactile consists of six soft and highly sensitive tactile modules which are placed on six sides of a cube to allow simultaneous measurement of the force in the positive and negative directions along the x, y and z axes. Some of the advantages of this sensor can be regarded as its high precision, excellent linearity (coefficient of determination r2=0.99), low cost and low noise. The accuracy of the sensor is 0.01 N, within a range of 4 N and therefore HexaTactile can be suitably attached to a robot end-effector for human-robot interaction applications. Then, using the proposed force sensor some control scenarios, including fixed admittance control and active admittance control are applied for human-robot interaction purposes. From the experimental tests, it has been revealed that the active admittance control solved the drawbacks of fixed admittance control, for the considered case studies.

Experiments were carried out using a pin-on-disc tribological tester in a flat-on-flat configuration in unidirectional sliding. Both counterparts were made from steel with 50 HRC hardness. The normal load was 20 N, the sliding speed was 0.4 m/s, the number of revolutions was 10,000. Before each test, one drop of L-AN-46 oil (0.08 ml) was supplied to the inlet side of the contact zone. The discs were textured using abrasive jet machining. Tribological effects of eight chevron-based textures were compared with that of the surface having circular oil pockets. All textures had the same pit-area ratios and depths. The untextured assembly was also tested for comparison. It was found that chevron-shaped dimples were sensitive to their angular orientation to the direction of sliding. The best tribological performances were achieved for chevrons inclined to the outer sides of the rotating discs.

The performance of metal cutting tools is drastically affected by the presence of hard coatings, which promote higher productivity and superior quality to the machined components. Nevertheless, the conventional properties are not capable to fully predict the behavior of the tool during the operation. The surface energy of solids is a characteristic which affects the contact interactions in sliding, i.e., adsorption, wetting and adhesion. However, one of the reasons why surface energy is often neglected in tribological studies is the lack of understanding concerned with the correlation between them, mainly for friction without lubricant. This work investigates the applicability of the surface energy as a property which can be associated with the performance of AlCrN and TiAlN coated materials.

The main aim of this work was to numerically investigate the effect of sequences of variable amplitude shear loading on contact tractions/stresses and on the development of life estimation methodologies for these more challenging loading histories. In this setting, a finite element (FE) model has been implemented in order to simulate a cylinder on plane contact problem for an aeronautical Al 7075-T651 alloy. High-Low (H-L) and Low-High (L-H) shear amplitude loading sequences under partial and gross slip conditions were considered in three different case studies. For the case studies where gross slip was involved, the proposed life estimation procedure was enhanced to include the effect of material loss due to wear. More explicitly, such procedure was based on the use of (i) the SWT (Smith-Watson-Topper) multiaxial fatigue model, (ii) the Theory of Critical Distances, (iii) Miner's cumulative damage rule and (iv) the numerical update of the contact surfaces profiles (for loading blocks under gross slip). The numerical analyses for the case studies under partial slip revealed that, when the presence of wear is neglected in the modelling, the Miner's rule provided a divergence between the expected life for the H-L and L-H loading blocks. This difference was considerably larger when gross slip took place. For the case study involving the presence of gross slip in one of the shear loading blocks, the calculated life tended to infinite when the damage generated by the high amplitude block is greater than a certain critical value. These studies are the basis for an experimental programme which will be carried out in the 4 actuators fretting fatigue rig of the University of Brasilia.

Deep valleys and flattened peaks are essential characteristics of the finished cylinder bore surface, which is known as the plateau surface. Generally, a honing process is done in three steps to achieve a plateau surface, which is costly and time-consuming and acts as a bottleneck for cylinder block machining line. The real challenge is to select optimum levels of honing process parameters to achieve desired surface characteristics with minimum machining time. The aim of this study is to examine the influence of the input parameters of the honing process on the surface texture of diesel engine cylinder bore. The Rk family parameters are used for surface roughness evaluation and the honing crosshatch angle, in accordance with engine design requirements, which was fixed for all experiments. Optimization by means of the desirability function technique allowed determining most appropriate conditions to desirable roughness (surface quality) and/or minimize machining time (productivity). Based on the findings of this study the conventional three-stage honing process has been replaced by the two-stage process. Using the proposed two-stage honing process the intended plateau surface in cylinder bores are achieved and a remarkable reduction in the honing process time is obtained. Consequently, the process efficiency is improved significantly.

The Precipitation Hardening (PH) Stainless Steel (SS) is considered as a promising alternative for aerospace and marine sectors owing to its good mechanical properties with high corrosion resistance. But the lower thermal conductivity and the presence of precipitates lower its machinability in terms of rapid tool wear. In this context, this study aims to analyze the dry, flood, MQL (Minimum Quantity Lubrication), and cryogenic machining with LCO2 in terms of tool wear for the turning tests of 15-5 PH SS. Apart from progressive flank wear, the machining performance of different cutting fluid strategies is compared by analyzing the crater wear, progressive power consumption, and surface roughness, microhardness, and microstructure of machined surface and chip. The performance of sustainable cryogenic machining is found superior in terms of lower tool wear, power consumption, subsurface microhardness. The relatively finer grain size and helical chip with smaller diameter are produced in the cryogenic machining while the better surface finish is observed for the flood machining in contrast to other cutting fluid strategies.

In the field of wearable robots, actuator efficiency and user safety are frequently addressed by intentionally adding compliance to the actuation unit. However, the implications compliance has on the actuator’s overall performance in different conditions and activities are not fully understood, largely due to single task-focused experimental evaluations of these devices. To overcome this, our paper analyzes the effects that changing mechanical compliance has on the actuator’s overall performance in different ideal conditions in an experimental test setup. The torque performance and electrical energy consumption of an orthotic, adjustable-compliance knee joint actuator are evaluated during emulated walking and sit-to-stand-to-sit movements. Furthermore, the feasibility of combined operation of a dual mechanical compliance configuration during walking is investigated, and its outcomes reported in this work. The results demonstrate that varying mechanical compliance can lead up to 50% energy savings compared to a no-compliance configuration and show that, in general, changing compliance level leads to either energy-optimal or power-optimal actuator performance, but not both.

This study presents the design and system integration of the 13-degree-of-freedom legged platform, GAZELLE. The goal of this research is to develop a fast and reliable biped platform for walking experiments. Rapid leg movement can increase robustness in walking stability. During external push or walking on uneven ground, fast leg movement can realize an abrupt change on the landing position. GAZELLE is characterized by a lightweight design, a link-driven structure for low leg inertia, a wide range of motion, and a direct-stacked fin air-cooling module. The actuator is designed using a special type of harmonic drive (lightweight CSF type) and a 200 W brushless DC motor with high power density. The knee and ankle joints are link-driven; hence, the actuators can be placed on the upper position, and the leg inertia is reduced. A novel air cooler design for the cylinder-type motor, which is extremely light and highly efficient, is introduced herein and realized by stacking cooling fins to the motor housing. This study also includes a brief introduction of a stabilizing controller and the walking experiment results of GAZELLE.

Additive manufacturing induces a microstructural anisotropy in its components, that reflects on their mechanical properties, and, in turn, on their machinability. In this paper, the tool wear when milling laser powder bed fused Ti6Al4V parts with four different build-up orientations was evaluated. The tool wear was qualitatively and quantitatively examined, and assessed indirectly by analyzing the chip morphology and the machined surface quality. This study demonstrates that the tool life decreases gradually up to 40%, going from machining horizontally manufactured samples to vertically manufactured ones. Furthermore, a novel interpretation of the correlation between the tool life and the additive manufacturing-induced anisotropy of the part was given.

Friction influences the formability in sheet metal forming processes. It depends on the local contact condition between tool and sheet metal. Therefore, precise estimation of real area of contact is the first step for an accurate prediction of friction. In this study, a multi-scale contact model is developed to predict deformation of asperities on a rough uncoated and coated surfaces under normal load. The model accounts for the coating thickness and material behavior of coating and substrate. Finite element simulations are performed to determine the contact pressure of single asperities of different sizes. These are used to determine the real area of contact. The model is validated relative to the experiments performed on uncoated and zinc coated steel sheets.

It has long been appreciated that there are many applications of tribology in the geological sciences. These range in scale from microscopic levels to those of intercontinental tectonic processes. Some of the key aspects of geotribology are briefly discussed to illustrate the advantages of such an interdisciplinary approach, before exploring the even greater benefits of applying tribological methods to many aspects of archaeology. That discipline comprises a vast array of physical evidence that derives from tribological processes and cannot be credibly explained by traditional archaeology. Many of these processes are briefly described, and the methodology required to define and elucidate them is discussed. The paper concludes that, for the further development of archaeology and the study of rock art, it is essential to establish a sub-discipline of archaeotribology.

Graphene and modified graphene can provide exceptional lubrication when used as additives. Here, we applied several types of graphene on steel tribo-couples to perform friction tests. The results indicate that the solution concentration and processing method regarding the graphene-containing alcohol solution can significantly affect the lubrication performance. Graphene nanoflakes aggregated on the sliding interfaces and underwent structural transformation under high contact pressure after the alcohol completely evaporated. The wear track and wear scar were then effectively protected by the in situ as-formed tribolayer. In contrast, a tribolayer could not form when the tribo-couples slid in a solution environment, as the graphene adsorbed on the contact area could be removed away by the alcohol.

The fretting capabilities of 690 alloy against 405 stainless steel were evaluated through a series of tube-plate tests in different experimental conditions. The results indicated that as the temperature increased in air, the wear volume and wear depth increased first until reaching a maximum value at 90 °C and then decreased. This was attributed to spinel oxides formed above 200 °C in combination with adhesive wear, which contributed to oxidation resistance and a reduction of interfacial wear, resulting in the decrease of wear volume and wear depth. Metallic nickel, iron and chromium were observed in water, which indicated low oxidation, associated with lower wear damage.

Reducing mechanical losses in internal combustion engines has been a recurrent research topic over the past few decades. Despite mechanical losses are a key issue that should be carefully addressed to reduce fuel consumption and emissions, its distribution amongst engine elements is barely covered in literature. Recent work has shown the potential advantage of using low viscosity engine oils to reduce fuel consumption, however, there is reduced knowledge on mechanical losses distribution under transient conditions. In this work, a model is presented that predicts not only the total friction losses of an engine, but determines the amount of friction energy lost in piston-ring assembly, engine bearings, camshaft and engine auxiliaries in driving cycles representing a real driving route. The stationary mechanical losses engine maps can be used due to non-dependence on mechanical losses with temperature in warm driving cycle conditions. The final results of the simulation predicts, with 2% error, fuel consumption, energy expended by the driven wheel and mechanical losses of the engine. This methodology reduces the computational cost to estimate key engine parameters in a real driving cycle such as: mechanical losses and its distribution, fuel consumption... as the total calculation time is 10 s per cycle simulated.

Hydraulically actuated manipulators are commonly used for material handling or at construction sites due to the high power density of hydraulic systems. Dig assistance systems or payload monitoring systems for excavators become more common to increase the efficiency and productivity. In this paper, a novel approach for estimating the dynamic parameters of a payload (including the mass) attached to the last link of a hydraulically actuated rigid body manipulator is proposed. Motion equations for the open chain rigid body system including the payload are derived. The motion equations are formulated as a linear regression model exploiting the linearity in the base dynamic parameters. Furthermore, a dynamic model for the neglected closed kinematic chains and the friction is proposed. A least squares optimization problem for minimizing the error between the model based torque and measured torque with respect to the payload parameters is defined. The optimization problem is simplified with assumptions on the center of gravity and the inertia of the payload, which leads to a more robust estimation of the payload mass with a recursive least squares algorithm. Post processing of the estimated payload is suggested and heuristics for the calculation of characteristic values like the accumulated handled mass are shown for the special case of a material handling and an earthmoving excavator. Finally, the novel approach for the payload estimation is validated on both experimental excavators for typical working cycles. The overall performance meets the requirements of ± 3%.

This paper analyses the kinematics and dynamics of an over-constrained parallel mechanism with four degrees of freedom providing Schönflies motion with infinite tool rotation. Despite its limited motion capability in one translational degree of freedom, the proposed mechanism has several potential uses, such as assembly of electronic components or fabric cutting. Firstly, the instantaneous kinematic problem of the investigated mechanism is presented, which includes formulating the inverse kinematics for the position, velocity and acceleration of the mechanism. Then, singular configurations of the manipulator are studied, based on the obtained Jacobin matrices. Secondly, based on the foregoing kinematic relations and the concept of link Jacobian matrices, the dynamic model is formulated by means of the principle of virtual work. Finally, the correctness of the derived models is verified by comparing the results obtained from the formulated models with those obtained using MATLAB Simscape Multibody.

In this work, the morphology, thickness, chemical composition and mechanical properties of the tribofilm formed by a fully formulated CVT fluid are investigated by multiple techniques and linked to the frictional and wear characteristics of a pin-on-disc tribosystem. It is found that the tribosystem shows higher friction and wear when tested at 150 °C than at 80 °C. The main reason is that although the morphology and thickness are similar, the tribofilms formed at different temperatures have different chemical compositions and mechanical properties. The tribofilm formed at 150 °C is Fe richer and has greater hardness and shear strength, which leads to a higher tribochemical wear rate and a greater interfacial shear force.

The rheological behavior of many lubricants used in hydrodynamic bearings can reasonably be modeled using the Bingham plastic material model. This behavior is characterized by a strong discontinuity, from a pure solid state to a viscous fluid state depending on the local shear stress. In literature three methods have been presented to model a Bingham plastic lubricated film. A full CFD and thus expensive, numerical simulation has been used. A general Reynolds equation based simulation has been used, however with a less accurate numerical regularization of the material discontinuity. Or a general Reynolds equation based simulation has been used, but with a severe reduction of the geometric complexity. In this paper, an ’exact’ thin film lubrication simulation for a Bingham plastic fluid is presented. The model is said to be exact in the sense that it requires no additional approximations to those used in the derivation of the general Reynolds equation, and requires no numerical regularization of the Bingham plastic fluid model and can still be used on any lubricating film geometry. Simulations on both infinite and finite journal bearings shows that the results of this new method are in good accordance with literature, demonstrating the validity of the method.

In order to enhance component performance, material sustainability, and service life, this study presents the tribological behavior of different austempered AISI 5160 steel specimens with shot peening. All the specimens were austempered for 2 h, then followed by shot peening to study the effect of shot peening and bainite morphologies on the wear and friction behavior. The microstructures, hardness, and residual stress of specimens were studied by optical microscopy, scanning electron microscopy, Vickers micro-hardness, 3D-profiler, and X-ray diffraction. Shot peening produced higher hardness on soft austempered specimens, rather than on hard austempered specimens. Compared with non-shot peened austempered disk specimens, the wear reduction of disk specimens with shot peening is up to 73%.

Auxiliary bearings (AB) support the rotor and protect the magnetic bearing (AMB) system when the AMB is disabled due to power loss or excessive loads. The paper demonstrates that installing a damping device along with the AB can yield extended AB fatigue life, protect the AMB, and reduce vibration, contact force and AB heating. A squeeze film damper (SFD) is an energy dissipation device that has been widely used in the turbo-machinery industry, and as demonstrated in the paper can also work effectively in combination with an AB. Usually, the SFD implements a supply groove to ensure adequate lubricant flow into the film lands. The supply groove can provide significant added mass coefficients and significantly influence the overall impedance of the SFD. Past literature has analyzed the transient response of the rotor dropping onto AB's with squeeze film dampers, none though have considered the influence of the SFD's center groove and its added mass effect on rotor's drop behavior. This paper develops a high fidelity finite element grooved SFD model considering the fluid inertia, and an effective groove clearance is used following the practice appearing in the literature. SFD force coefficients are benchmarked with results of a linear fluid inertia, bulk-flow model developed in the literature, before including them in the rotor – AB system model. The SFD model is integrated into a high fidelity nonlinear auxiliary bearing (angular contact ball bearing) model, which considers the movements, contact force, stress, and temperature of bearing balls, the inner race and outer race. The instantaneous reaction forces from the SFD are calculated with a finite element based solution of Reynold equation at each time step due to the intermittent and large sudden loads. The flexibility of the rotor is included utilizing a Timoshenko beam, finite element model. The fatigue life of the auxiliary bearing when integrated into the SFD is also calculated based on the rain flow counting method. The influence of the added mass of the SFD on the rotor's drop behavior is demonstrated showing that the added mass increases the contact force and peak temperature and reduces the fatigue life of the AB. Therefore, the added mass effect of the SFD should be considered to avoid over predicting the AB fatigue life. The influence of the SFD clearance on the rotor's drop behavior is also studied showing that an optimal clearance exists for increasing the AB fatigue life. Too small of a clearance will yield excessive damping making the effective stiffness too large, and causing high contact forces. Too large of a clearance lowers damping which may lead to a destructive backward whirl. This paper provides key guidelines for auxiliary bearing damper system design.

We address in this paper the problem of planning motion of free floating robot with state constraints. Due to the conservation of angular and linear momentum during the in-air motion, the problem is two-fold: one needs to design, in addition to the in-air motion, the initial impulse that imparts the robot with the appropriate momentum to perform a desired motion. The existence of state constraints such as joint limit makes the planning problem even more challenging. We propose in this paper a new method to address this problem. The method is a homotopy method which deforms an arbitrary path connecting the desired initial and final states to a feasible trajectory between these states, that is a trajectory that meets the system’s dynamics and constraints. From this trajectory, the method extracts both the controls and initial momentum needed to perform the motion. The deformation of path is leaded by geometric heat flow which is defined by a Riemannian metric that encodes the system dynamics and state constraints. We illustrate the method by designing somersault motions for a diver robot.

This article is concerned with the discontinuous dynamical behaviors of a class of single degree of freedom oscillators with linear and nonlinear springs and viscous dampers in the co-existence of bilateral rigid impact and friction through the theory of flow switchability and flow barrier in discontinuous dynamical systems, where considering the inequality of static and kinetic friction coefficients. By the analysis of vector fields and G-functions on the corresponding discontinuous boundaries for such an oscillator, the analytical conditions of all possible motions are established, which are in the form of a set of inequalities or equalities and can be used for the selection of control parameters in this kind of system. Additionally, based on mapping dynamics, the two-dimensional basic mappings are defined, the analytical predictions and stability analysis of different periodic motions are accomplished. Finally, our theoretical results are further demonstrated by numerical simulations by means of dimensional and dimensionless parameters with graphical illustrations of the time histories of displacement, velocity, G-function and the trajectories in phase space for the passable motion, stuck motion, impact motion, grazing motion and periodic motion etc., and stick and grazing bifurcation scenarios varying with excitation frequency and amplitude are also given.

Kenneth Henderson Hunt, see Fig. 1, was the Foundation Professor of Engineering, and the inaugural Dean of the Faculty of Engineering at Monash University, Victoria, Australia. He was the Dean of Engineering from 1961 until 1975 and then served as the Chair of Mechanism from 1976 until 1985. He is remembered as the scientist who rediscovered Ball's theory of screws and who made significant contributions to screw system theory which he applied to the kinematics of spatial mechanisms, shaft couplings, and robotics. Kenneth authored two classical books Mechanisms and Motion and Kinematic Geometry of Mechanisms, and co-authored the more modern text Robots and Screw Theory: Applications of Kinematics and Statics to Robotics. He was also one of the founding fathers, contributing to the foundation act with the initial member organizations, of the International Federation for the Theory of Machines and Mechanisms (in 1998 the official name was changed to IFToMM, acronym for the International Federation for the Promotion of Mechanism and Machine Science). The federation was officially born in 1969 and Kenneth served on the first Executive Council and was the founding chairman of the Australian Committee.

This paper presents a new modes switching control method based on a dual-motor centralized and distributed coupling drive system, which can achieve the centralized and distributed coupling drive and reduce the modes switching shock to improve electric vehicle dynamics performance. Initially, the influence of the switching speed on the shock is analyzed and the models of each modes switching stage are established. Furthermore, a stage-by-phase multivariable combination controller based on the control of position, velocity and force of the actuators is designed, and a load torque state observer is developed to estimate system interference. Finally, the shock suppression effect is testified by the upshift process simulation and the experiments of a centralized and distributed coupling drive electric vehicle. The research shows that the peak value of the switching process with the controller is 9 m/s3, which is lower than the recommended value of 10 m/s3. It laid the theoretical foundation for solving the mode switching problem of the centralized and distributed coupling drive electric vehicles.

In this paper, a simple and effective methodology for judging the singularities of planar linkages is presented, which is based on Assur groups. The methodology determines the geometrical configurations of the Assur groups in singularities. Based on the singularities of a simple two-bar group, the possible singularities of all Assur four-bar and six-bar groups are given by the concept of instant centers. Then the general process and rules of determining singularities are obtained and shown through several examples of the 1-DOF planar linkages. These linkages include the two six-bar linkages and the several eight-bar linkages composed of Assur six-bar groups. The singularities of them verify the proposed methodology, which reveals that the singularities of a linkage only depend on the Assur groups. Therefore, as long as the singularities of Assur groups are determined, all the possible singularities of the linkage composed of these groups can be determined. This methodology is independent of linkages, so it is universal for all planar multi-bar linkages which can be divided into these Assur groups.

Two optimal design methods are proposed for the dimensional design of parallel manipulators, considering their dynamic performance over the desired ranges of motions, velocities, and accelerations. The first method, termed as the extrinsic method, directly minimises the actuator forces/torques within the desired safe working zone of the manipulator, for typical velocities and accelerations of the end-effector. The second method, namely, the intrinsic method, minimises a measure of the manipulator’s inertia, as reflected at the actuators, over the said safe working zone. Case studies on the design of 3-RRR and 3-RRS manipulators are presented to illustrate the proposed methods. Numerical studies show that the optimal link dimensions obtained through these conceptually disparate methods are fairly similar. Naturally, the dynamic performances of the resulting manipulators are also comparable, which are found to be significantly better than that of arbitrary designs respecting the same constraints.

In many technical systems, rolling bearings are critical machine elements concerning accuracy and lifetime. Their load distribution and radial displacement are directly linked to the accuracy and the fatigue life of rolling bearings. However, load distribution and radial displacement form a complex interdependency. Geometric deviations further influence this mutual connection. Although there are several approaches to determine the load distribution and the radial displacement, most of them are either too simplistic, allowing only the consideration of dimensional deviations, or too sophisticated and therefore unsuitable for a statistical evaluation of geometric deviations. Hence, the main purpose of this contribution is to provide a method for the determination of load distribution and radial displacement of cylindrical roller bearings that allows the consideration of geometric deviations as well as statistical evaluation of these deviations. Moreover, applying the method to a use case shows, whether the consideration of geometric deviations in the determination of load distribution and radial displacement is reasonable. The novelty of the contribution is, therefore, the provision of a statistical variational simulation framework for the analysis of load distribution and radial displacement of rolling bearings.

The ability of changing aircraft wing shape or geometry has drawn great attention of researchers in the past decades. This paper proposes a new approach to design a lengthwise morphing structure for an airfoil morphing wing. The structure is composed of n planar mechanism units. Each unit is designed to have 3 degrees-of-freedom (DOFs) that can be fully controlled by two actuators using lockable joints. This structure is reconfigurable through dual mode switching by locking specific joints. The end-effector of the mechanism can reach any desired position and the morphing wing can change to any desired shape. When locking three or four actuators, the structure turns into a statically determinate or indeterminate truss structure to withstand required loads. Force analysis for the structure during morphing motions is conducted based on statics, and an optimization method is used to determine the appropriate number of actuators and their placements. Prototypes with or without skins are fabricated to verify the feasibility of the design.

The branches of motion in the configuration space of a reconfigurable linkage can intersect in different ways leading to different types of singularities. In the vast majority of reported linkages whose configuration spaces contain multiple branches of motion the intersection happens transversally, allowing local methods, like the computation of its tangent cone, to identify different branches by means of their tangents. However, if these branches are of the same dimension and they intersect tangentially, it is not possible to identify them by means of the tangent cone at the singularity as the tangent spaces to the branches are the same. Although this possibility has been mentioned by a few researchers, whether linkages with this kind of tangent intersection of branches of motion exist is still an open question. In this paper, it is shown that the answer to this question is yes: A local method is proposed for the effective identification of branches of motion intersecting tangentially, and a method for the type synthesis of linkages that exhibit this particular type of singularity is presented.

This paper presents the development of a finger rehabilitation robot (FRR) for active and passive training to fulfill the requirements of different rehabilitation stages. In the design, an antagonistic pair of pneumatic muscles (PMs) are utilized to exert a bidirectional force for passive training, and a controllable magnetorheological (MR) damper is used to provide a damping force for active training. In this paper, first, a detailed illustration of the mechanical design of the FRR, including the driving, transmission and actuating mechanisms, and the damping device, is presented. Subsequently, the kinematic analysis and simulation are described, followed by the static and dynamic analysis of the designed FRR. This paper details the static force transfer of the transmission mechanism, and the establishment of dynamic equations for the passive training system. Finally, an experimental set-up is established, and several passive and active training experiments are conducted for the performance evaluation of the FRR prototype. The results validate the feasibility and stability of the developed FRR.

This work investigated the effects of sliding speed on tribological behavior of AA 7075 petroleum casing in simulated drilling environment by pin-on-disc wear test. The main wear mechanism of AA 7075 disc at low sliding speed (0.0628 m/s and 0.157 m/s) was abrasive wear and oxidative wear at middle sliding speed (0.314 m/s). As sliding speed increases to higher sliding speed (0.471 m/s and 0.628 m/s), adhesive delamination wear dominated the wear process. The tribo oxides layer can efficiently protected the alloy substrate only at sliding speed of 0.314 m/s. At higher sliding speeds, tribo oxides layer were removed quickly once it was formed due to its internal fractures of tribo oxides and lower bonging strength with substrate.

The nano scale motions of piezoelectric actuated nano-positioning systems are very sensitive to operating tasks, external disturbances, as well as variations of system dynamics. In this paper, a data-driven Iterative Feedback Tuning (IFT) based Active Disturbance Rejection Control (ADRC) approach is developed to optimize the control performance by conducting controller parameter tuning iteratively from experimental test data. In particular, a parameterized input-output form of the linear ADRC controller is derived for the nano-positioner, where the IFT algorithm is applied to solve the established optimization problem to get the optimal control parameters. The proposed method is verified in simulations where the selection of control criterion and the impact of update step-size are also discussed. Single-axis and dual-axes real-time experiments are finally conducted on an X-Y piezoelectric actuated nano-positioner, which demonstrate significant performance improvement on nano-positioning and tracking over the conventional ADRC method.

A new non-symmetric 5R-SPM is introduced and a geometrical approach is developed to analyze its configurations and singularities. The proposed methodology determines the type of configuration of a 5R-SPM, i.e. regular, singular, or out-of-workspace and also the type of singularity, i.e. instantaneous or finite, only based on geometric parameters and without solving verbose kinematic equations. It also provides insights into the workspace and singularities of 5R-SPMs, in the preliminary stage of design. The mechanism was analyzed by both the new geometrical approach and conventional methods for comparison. The geometrical approach could intuitively detect all the singularities observed by the Jacobian matrix and the kinematic analysis, with more details on the type and characteristics of each singularity. The dimensional synthesis for the designed mechanism was also performed based on the type and existence of singularities. The proposed methodology might be further developed to specify the configurations and singularities of general SPMs and also to introduce a geometrical measure for singularity closeness.

This study aims to improve the static and dynamic characteristics of a helical gear pair by optimizing the parameters of linear tip-relief. The static analysis intends to reduce the maximum contact stress to extend the service life of the gear pair, while the dynamic analysis attempts to reduce the dynamic transmission error (DTE). First, mathematical models of a helical gear pair generated by rack-cutters with linear tip-relief were developed based on the theory of gearing. Tooth contact analysis enabled us to estimate static transmission error and contact pattern of the gear pair under various assembly errors. Additionally, the contact stress contour and mesh stiffness were calculated through loaded tooth contact analysis by using finite element analysis. A dynamic model of the helical gear pair was also developed to simulate the dynamic characteristics under various rotational speeds, including DTE and vibration energy. Finally, the simulation results revealed that the high contact stress, DTE, and vibration energy of the original helical gear set were successfully reduced by the improved linear tip-relief parameters.

The application of hybrid mechanisms in the field of humanoid robots has attracted significant attention. A novel eight-degree-of-freedom hybrid manipulator is proposed to realize a kinematic function similar to that of the human arm. A general method for solving the inverse displacement problem of hybrid mechanisms is given, and the proposed humanoid robotic arm is taken as an example to demonstrate the solution process of this method. Furthermore, a closed-form solution for the inverse displacement problem of the hybrid humanoid robotic arm is derived by using the given method based on screw theory, exponential product formula, and Paden–Kahan subproblems. In addition, the problem of verifying and selecting the appropriate solutions according to the starting postures is also illustrated in a series of simulation experiments. Simulation experiment results show that there are (at most) 32 sets of solutions for the proposed humanoid robotic arm according to the same target position-orientation matrix and the given redundant input variables, and the accuracy of the proposed method for solving the inverse displacement problem is verified.

To improve the wide-temperature applicability of amorphous carbon-based films, a novel a-C/(WC/a-C) film compositing of a-C nano-layers and super-latticed WC/a-C nano-multilayers was proposed and successfully fabricated on M50NiL substrate by an unbalanced magnetron sputtering system. For comparison, a monolayer a-C film and a super-latticed WC/a-C film were also prepared on the same substrates. The microstructures, mechanical properties and thermal stability of the as-deposited films were investigated. Particularly, the tribological behaviors of films against M50 counterpart were evaluated at the temperatures ranging from 25 °C to 350 °C. The results showed that because of the excellent thermal stability of super-latticed WC/a-C sublayers, the a-C/(WC/a-C) film has effectively overcome the poor tribological performance of a-C film at high temperatures (≥200 °C). While benefiting from the good toughness of a-C sublayers, the a-C/(WC/a-C) film showed significant better wear resistance than the WC/a-C film at the temperatures of 25–200 °C. The best wide-temperature applicability of the novel a-C/(WC/a-C) film should be attributed to the favorable mechanical properties, together with the formations of carbon-rich transfer film at 25–150 °C and WO3-rich transfer film at 200–350 °C.

This paper proposes a new Bricard-like mechanism composed of three anti-parallelogram units. First, the configuration and connection of the Bricard-like mechanism are given. Second, the mechanism is simplified as a spatial single-loop overconstrained 6R mechanism with variable links’ lengths and its Denavit-Hartenberg (D-H) parameters are obtained by identifying the six revolute joints axes. Third, the degree of freedom of the mechanism is calculated through the closure equations, and kinematic paths of output variables are plotted with respect to the input variable. Then, a serial of Bricard-like mechanisms are connected to construct the deployable mechanism. Finally, three prototypes of the Bricard-like mechanism and the triangular prism deployable mechanism composed of four Bricard-like mechanisms are designed and fabricated to verify the feasibility of the proposed method and analysis.

The total variation on graph (TVG) is a powerful vertex domain index for measuring the smoothness of graph signals, but its performance is closely related to the underlying graph. Since the horizontal visibility graph can better reflect the dynamics characteristics of bearing vibration signals than the path graph, the underlying graph of TVG is designated as horizontal visibility graph. The vertex domain index TVG defined on horizontal visibility graph is called simply as TVHVG in this paper. For better distinguishing the different states of rolling bearings, the bearing vibration signal is converted into the graph signal indexed by its horizontal visibility graph, and the vertex domain index TVHVG is extracted as the single fault feature. Based on TVHVG feature extraction and Mahalanobis distance classification, a novel fault diagnosis method for rolling bearings is proposed. The proposed method is applied to analyze two sets of experimental data containing normal and faulty rolling bearings. The results indicate that the proposed method can diagnose the bearing faults with different types and degrees effectively, and the vertex domain index TVHVG is superior to some classical time domain indexes in distinguishing the different states of rolling bearings.

“Two rotational degrees of freedom” and “one translational degree of freedom” (2R1T) parallel mechanisms (PMs) have been successfully applied to develop five-axis hybrid robots for machining purposes. However, the number of passive joints contained in current 2R1T PMs has not still reached the minimum, which may impede these robots from having high stiffness. This study has put forward the concept of ultimate constraint wrenches acting on the PM's moving platform, and this concept was used to reduce the number of kinematic joints to a minimum. Based on the reciprocal screw theory, an ultimate constraint wrench system of the 2R1T PMs was found, and then a series of novel overconstrained 2R1T PMs with the fewest kinematic joints, containing three or four branches, were constructed. Furthermore, based on a developed overconstrained four-branch 2R1T PM RPU-2UPR-RPR, a type of five-axis hybrid robot with the fewest kinematic joints was constructed, which demonstrated good application prospects.

Based on the multi-support mode of low-pressure rotor and fan rotor of gearbox in GTF (Geared turbofan engine), the coupling gear-rotor-bearing dynamics model is established in this paper. The effect of bearings on both rotors on the dynamic behavior of the GTF transmission system have been explored and quantified, especially for the influence of location of bearings on both rotors on the load sharing behavior of the star gearing system in GTF gearbox. Axial, transverse and rotational motions of double-helical gears are included in the dynamic model, in which the time-varying support stiffness of bearings, the gear mesh stiffness with phase relationship between multiple meshes and comprehensive errors are fully considered. The results show that position of bearings on both rotors could affect the load sharing performance and maximum floating amounts of members in star gearing system of GTF gearbox, therefore, the location of bearings on rotors can be rearranged to achieve better performance in vibration control and load distribution of the system.

This paper proposes a new method for control of nonlinear multi input – multi output (MIMO) mechanical systems that incorporate viscoelastic dampers (VED) for reducing undesired vibrations of actuators. To this end, a control algorithm is proposed based on considering various characteristics of the described dynamical systems (namely mechanical dynamics, viscoelasticity and actuator dynamics) in generation of control inputs guaranteeing convergence of system response to desired reference signals. This procedure features three consecutive parts within the control loop which are conducted iteratively at each control sample. At each sample, initially necessary forces and moments exerted to mechanical system are calculated as virtual control inputs generated based on a MIMO discrete-time sliding mode control (DSMC) algorithm. As the aim of control model is obtaining a closed-loop system without resulting in notable vibrational effects, undesired chattering effects should be eliminated from inputs generated by DSMC. This objective is attained by calculation of appropriate input bounds. Next, an additional virtual input is assigned corresponding to viscoelastic strain such that virtual mechanical input from previous part of the control loop is generated. To this end, Maxwell model for viscoelastic material is considered. Finally, actual controller input is generated such that all virtual control objectives are satisfied. The effectiveness of control procedure is numerically illustrated for a 3-PRR manipulator.

The forging manipulator is a complex industrial robot with a spatial serial-parallel hybrid structure and multiple degrees of freedom, and the decoupling ability among different motions is a critical performance index for it. A novel kind mechanism of forging manipulator that can achieve decoupling between lifting and horizontal buffering motions was proposed, by integrating the improved Hoeckens straight-line mechanism with the buffering mechanism. It is easy to realize motion control of such forging manipulator, which indicates that it has potential application prospects. Considering the motion-decoupling characteristics as well as the practical working conditions, the whole architecture of this novel forging manipulator was divided into three independent single-degree-of-freedom sub-mechanisms. Then, with the elastic deformations of each component taken into consideration, the elastodynamic model of each sub-mechanism based on the finite element theory and the KED (Kineto-Elastodynamic) analysis was established for more accurate dynamic responses. The Newmark stepwise integration method was used to solve the elastodynamic equations, and the response characteristics of displacement, velocity, and acceleration of the manipulator were obtained, providing important theoretical references for further optimization designs and practical applications of this novel mechanism for forging manipulators.

Flexible beams of variable effective length, serve both transmission and actuation functionalities in compliant mechanisms, have been employed in many devices, e.g., thermal actuators and continuum robots. This difunctional feature is favorable when utilized for operations in confined space. However, the length variation introduces modeling difficulties, which poses a new challenge to designers. To accurate model flexible beams of variable effective length and characterize the behaviors of associated compliant mechanisms form the primary objectives of this study. The chained beam constraint model is revisited and extended to model beams of variable effective length. Modeling of a chevron shape thermal in-plane microactuator and a continuum mechanism are provided to demonstrate the effectiveness of the proposed method. The predicted results have a high degree of accuracy as compared to experimental results and nonlinear finite element results.

Though finite length squeeze film dampers (FLSFD) are practically and effectively applied to vibration attenuation, they have not been popularly used in bevel gear systems (BGS) due to the limitations of the existing models of FLSFD. The present work proposes a general approach for modeling and calculating the nonlinear oil-film force of FLSFD, which is introduced into system motion equations to model the BGS supported on FLSFD mathematically. Comparisons with conventional methods show the superiorities of the proposed model in terms of computational accuracy and versatility. The damping characteristics of FLSFD are examined by comparing the dynamic behaviors of the BGS with and without FLSFD. Besides, the response sensitivity of the system to different parameters, including the length and radial clearance of FLSFD, is also discussed. The results show that FLSFD can significantly reduce the vibration amplitude passing through the critical speeds and suppress the nonlinear characteristics of the system, such as bistable state responses and jump phenomena. The results also reveal a dependence of the damping performance on the choice of the FLSFD design parameters.

Random and interval mixed uncertainties (RIMU) universally exist in engineering, thus it is necessary to construct a reasonable model for analyzing the probabilistic safety degree in this case. Aiming at analyzing the probabilistic safety degree efficiently, the existing double-loop nested optimization (DLNO) algorithm for estimating the upper and lower bounds of failure probability (FP) is firstly investigated under RIMU. It is proved that the upper and lower bounds of FP obtained by DLNO actually equal to the maximum and minimum of all approximate FPs with respect to the possible discrete points of interval variables. Secondly, it is found that the failure domain corresponding to the upper bound of FP is similar to that of time-dependent reliability under random uncertainty. Based on this similarity, the inequality relations are established for the real upper and lower bounds of FP and those obtained by DLNO, and the Kriging surrogate model methods are proposed to solve probabilistic safety model under RIMU efficiently. Additionally, this efficient solution strategy is further extended to the time-dependent structure under RIMU. Finally, numerical and engineering examples are used to demonstrate the reasonability and efficiency of proposed methods.

Recent researches proved that bearing friction can be largely reduced with an oleophilic (no-slip) surface sliding against an oleophobic (slip) surface. The present work investigates the applicability of the slip/no-slip concept to 2D elastohydrodynamic lubrication (EHL) problems. Numerical analysis of isothermal EHL point contact is conducted under pure rolling conditions with the critical shear stress slip model. The challenge of determining the slip direction upon the attainment of the critical shear stress value in 2D problems is resolved by using a linear complementarity principle. The effect of boundary slip on bearing performance in terms of film thickness and friction is evaluated.

The third body approach deals with friction as a problem of third body rheology. Using a multibody meshfree model, we report influence of cohesion on third body rheology and friction at a dry sliding contact. With cohesion increasing from 0.0001 to 20 GPa, friction firstly increases linearly then transitions to a constant value, based on which three friction regimes are identified. Low cohesion (0.0001–1 GPa) is featured by lamellar flow; medium cohesion (1–5 GPa) triggers formation of strong inclined force chains; high cohesion (5–20 GPa) results in generation and rolling of agglomerates. How third bodies accommodate velocity gradient and transfer load are carefully examined. The results provide a possible novel approach of material design to monitor the coefficient of friction.

Molybdenum dithiocarbamate (MoDTC) is well-known as a friction-modifier in engine oil but has wear accelerating effects on DLC/steel sliding contact. Since MoDTC was reported degradable to other materials, the effect of each material on wear acceleration has not been clarified yet. Therefore, it is necessary to divide which Mo-derived compound has a major role to enhance wear. Thus, powder-type MoDTC, MoO3, Mo2C, MoS2, and Mo were dispersed into Poly-alpha-olefin (PAO), and tested on a-C:H and Si-DLC against steel ball at room temperature. For Mo2C, MoDTC, and MoO3, the specific wear rate of a-C:H was approximately 3.4 × 10−5, 3.2 × 10−6 and 1.5 × 10−6 mm3/Nm, respectively. MoDTC indicated higher affection than MoO3 regardless of the particles’ hardness. Si-DLC showed better wear prevention compared to a-C:H.

Nowadays tendency is the practice of engine downsizing with a turbocharger, to increase fuel economy and decrease emissions. For both design and analysis, a reliable rotor-bearing model is mandatory. In turbochargers, floating-ring bearings support the rotating shaft, with a double-acting thrust bearing, to support axial force imbalances from the compressor and turbine gas flows. The typical turbocharger is highly nonlinear due to the high rotational speeds achieved. Therefore, a turbocharger model, supported by floating-ring and thrust bearings, is developed, considering both bearings nonlinear behaviour, including temperature variations in oil films. The thrust bearing model contemplates a full thermo-hydrodynamic evaluation, while the floating-ring bearing investigation is somewhat simplified. The analysis focuses on the thrust bearing influence in the turbocharger lateral vibrations.

To enhance wear properties of titanium alloys, in situ titanium matrix composites (TMCs) were synthesized by a melting cast method with (TiC + TiB) volume fractions of 0, 2, 4, 6, 8, and 10%. The results indicated that tribological properties of TMCs were increased owing to the dispersed distribution of (TiC + TiB) reinforcements, which improved the ability to resist the surface shear stress. Moreover, the stable transfer layer formed during wear reduced the shear strength and limited the direct interaction at tribo-pair interfaces to enhance surface hardness and wear resistance effectively. Consequently, the wear mechanism appeared to transitioned from the severe adhesive and oxidative wear gradually to the slight adhesion, abrasive, and oxidative wear along with reinforcements content increased.