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A mechanical system with clearance joints is well known as a nonlinear dynamic system that may exhibit chaotic responses under certain conditions. In the previous literature, the model for clearance joint is extensively investigated since it plays a significant role in prediction of kinematic and dynamic behavior of the system. A large volume of the literature only focuses on radial clearances, whereas, due to manufacturing and assembling errors, axial clearances also exist in joints, which have been scarcely considered. In this study, a comprehensive model for 3D revolute joints with radial and axial clearances is proposed. An experiment of the 3D revolute joint with clearances is firstly conducted to reveal the characteristics of the relative motion between the journal and bearing. According to the kinematic features, a model for 3D revolute joints with radial and axial clearances is proposed. This model presents a comprehensive description of the contact modes in which a group of contact force models are employed to reflect different contact-impact phenomena. Thus, the axial movement of the journal relative to the bearing and misalignment between the two elements could be characterized by this model. Moreover, a numerical simulation of the experiment is performed to validate the model presented in this study. Finally, a four-bar mechanism is taken as an example to illustrate its application and investigate the nonlinear dynamics of this system. List of symbolsO − i 1 i 2 i 3 Global coordinate system O − e 1 e 2 e 3 Local coordinate system R Radius (m) δ Penetration depth (m) F Magnitude of a force (N) M Magnitude of a moment (N m) K Generalized stiffness (N/m 1.5 ) D Damping coefficient (N s/m) υ Poisson's ratio of each sphere (i = 1, 2) E Young's modulus of each sphere (i = 1, 2), GPȧ δ Penetration velocity (m/s) δ − Initial impact velocity (m/s) s Half-length of contact area width (m) l Length of the contact area (m) p Pressure (m Pa) V Relative tangential velocity (m/s) V s Stick-slip switch velocity (m/s) V d Static-sliding friction switch velocity (m/s) μ s Static friction coefficient μ d Sliding friction coefficient 123 S. Yan et al. ω Angular velocity (rad/s) c Radial clearance (mm)

With the use of a scanning electron microscope, we observe specific microstructures of the mouthpart of the Italian bee (Apis mellifera ligustica), especially the distribution and dimensions of hairs on its glossa. Considering the erection of glossal hairs for trapping nectar modifies the viscous dipping model in analyzing the drinking strategy of a honeybee. Theoretical estimations of volume intake rates with respect to sucrose solutions of different concentrations agree with experimental data, which indicates that erectable hairs can significantly increase the ability of a bee to acquire nectar efficiently. The comparison with experimental results also indicates that a honeybee may continuously augment its pumping power, rather than keep it constant, to drink nectar with sharply increasing viscosity. Under the modified assumption of increasing working power, we introduce the rate at which working power increases with viscosity and discuss the nature-preferred nectar concentration of 35% by theoretically calculating optimal concentration maximizing energetic intake rates under varying increasing rates. Finally, the ability of the mouthparts of the honeybee to transfer viscous nectar may inspire a concept for transporting microfluidics with a wide range of viscosities.

The adaptive decomposition algorithm is a powerful tool for signal analysis, because it can decompose signals into several narrow-band components, which is advantageous to quantitatively evaluate signal characteristics. In this paper, we present a comparative study of four kinds of adaptive decomposition algorithms, including some algorithms deriving from empirical mode decomposition (EMD), empirical wavelet transform (EWT), variational mode decomposition (VMD) and Vold–Kalman filter order tracking (VKF_OT). Their principles, advantages and disadvantages, and improvements and applications to signal analyses in dynamic analysis of mechanical system and machinery fault diagnosis are showed. Examples are provided to illustrate important influence performance factors and improvements of these algorithms. Finally, we summarize applicable scopes, inapplicable scopes and some further works of these methods in respect of precise filters and rough filters. It is hoped that the paper can provide a valuable reference for application and improvement of these methods in signal processing.

In this paper, a novel miniature-step mobile robot with three degrees of freedom (DOFs) is developed based on the inchworm principle. This device, driven by a piezo stack actuator, utilizes a rhombic flexure hinge mechanism and four electromagnetic legs to achieve large stroke translation and rotation with high resolution on a platform. The design process of the rhombic flexible frame and the electromagnetic legs is described. The electric circuits for generating appropriate voltage signals are designed to control the legs to clamp to and release from the platform. In order to investigate the motion characteristics of the device, a series of experiments was carried out. The experimental results confirm that the device is capable of performing a 3-DOFs motion with a high resolution on a platform. Furthermore, the platform loading capacity allows some additional devices like a gripper or any other device for a particular application to be mounted on board. This enables the device's potential in a wide variety of applications.