查看更多>>摘要：The mechanical properties of polymer gear transmissions are dependent on the operating temperature. Therefore, the prediction of the temperature of polymer gears is an important step during the design process. In this regard, analytical methods provide simple equations to predict the bulk temperature, but its applicability is limited by the underlying theory.In this work, a detailed background of the theoretical models that affect the temperature rise phenomena of polymer gears is provided. The methods suggested by Hachmann (and its implementation on VDI 2736 standard), Takanashi and Mao are derived from this common theoretical background. The common points, strengths and limitations of the methods are provided.The methods are illustrated with a variety of numerical examples and compared to reference experimental results. This comparison allowed us to draw some conclusions, to provide recommendations for the application of these methods, and identify potential measures of improving their results.
查看更多>>摘要：It has been shown that one can guarantee a reachable workspace for a kinematically redundant robot after an arbitrary locked-joint failure if one artificially restricts the range of its joints prior to the failure. This work presents an algorithm for computing the optimal kinematic parameters and artificial joint limits for a robot to maximize this so-called "failure-tolerant workspace". The proposed technique employs a genetic algorithm that incorporates a novel method for selecting an initial population that results in fast convergence to high-quality solutions. The algorithm is illustrated on multiple examples of kinematically redundant robots and is shown to be computationally tractable even for robots that perform tasks in 6D workspaces.
查看更多>>摘要：The rotating vector reducer (RV reducer) is widely used in joint transmission of industrial robots. The moment rigidity and rotation precision of the non-standard angular contact ball bearings planetary frame rotor system (BPFRS) in the RV reducer have a significant impact on the service performance of industrial robots. This paper presents an improved dynamic model to study the moment rigidity and rotation precision of the BPFRS. The proposed model optimizes the theoretical method for calculating balls-races contact deflection and contact angle, which can more precisely describe the locus of the inner race groove curvature center. Furthermore, a moment rigidity test experiment is designed to verify the accuracy of the proposed model. On the basis, effects of different load conditions, axial preload displacement, numbers of balls, and combinations of inner and outer race groove curvature radius coefficients on moment rigidity and rotation precision of the BPFRS are analyzed, respectively. The results show that these factors have a significant effect on moment rigidity and rotation precision. Besides, dynamic characteristics of the spatial rotation trajectory of the reducer center are obtained.
查看更多>>摘要：Planetary bearings are the most complex and challenging components for health diagnostics among wind turbine and helicopter planetary transmissions. Classical spectrum-based diagnosis strategy for planetary bearings faces great challenges because of complex structures and strong modulation effects. This work develops a novel sparse learning based classification (SLBC) framework with the overlapping segmentation strategy to address planetary bearing health diagnostics. Our SLBC framework learns the reconstructive dictionaries for sparse representations of vibration signals and achieves robust recognitions with the sparse approximation criterion. Firstly, the overlapping segmentation strategy is introduced to fully leverage periodic similarity features and augment training datasets for sparse dictionary learning. Then, the category-specific sub-dictionaries are learned from the augmented training datasets in a data-driven fashion via K singular value decomposition. Finally, intelligent planetary-bearing fault recognition is achieved via the sparse approximation criterion. Our SLBC framework has been verified effective to classify three and four planetary-bearing health states with diagnostic accuracy of 100% and 99.98%, respectively. Comparisons with several advanced approaches have confirmed the superiority of SLBC in diagnostic accuracy, noise robustness, and computation time for planetary bearing health diagnostics.
查看更多>>摘要：Linkage synthesis includes three types of task specifications, which are motion generation, function generation and path generation. Generally, the three syntheses are treated separately. However, in some situations, linkage needs to complete two types of tasks, called hybrid tasks, simultaneously. In this paper, we present an analytical method to synthesize a multi-functional eight-bar linkage with a translational actuator to complete a hybrid task. The linkage can pass through 5 task positions for function generation and 5 task positions for motion generation simultaneously. To avoid highly nonlinear polynomial design equations, the linkage is separated into three loops to synthesize. The strategy of kinematic performance verification is proposed to obtain a non-defect linkage. Finally, a novel variable wing sweep mechanism for unmanned air vehicle is designed by using the multi-functional eight-bar linkage, which also validates the hybrid synthesis method. The result of this study provides a new design idea for linkage design.
查看更多>>摘要：In this paper, the design, optimization, and application of a parallel three-degree-of-freedom micro-nano motion stage for vibration-assisted milling are reported. This stage is driven by the piezoelectric effect to achieve precise position adjustment. A compound differential branch chain is designed to solve the poor stiffness of traditional branch chains and large deflection errors. Mechanical properties of the stage are theoretically, numerically, and experimentally investigated. The output displacement and natural frequency are weighed by orthogonal optimization. The open-loop tests on the prototype showed the stage performance such as hysteresis, tracking, and decoupling. Milling of typical microstructure surfaces is employed to demonstrate the effectiveness of the stage.
查看更多>>摘要：This paper studies the effectiveness of adopting mesh phasing for suppressing several particular modal responses in a typical split-path transmission. The dynamic model admits three planar degrees of freedom for each gear and considers time-varying mesh stiffnesses, which captures the effect of mesh phasing. The vibration modes of the system are analyzed for the time-invariant case with average mesh stiffnesses, and the characteristics of each mode shape are summarized. Then, according to the characteristic of rigid-body modes, a new method for eliminating the rigid-body displacement of a time-variant system is proposed. This method has a clear physical interpretation and is convenient to use. The modal equations are solved numerically after removal of the equation of the rigid-body mode. It is found that appropriate mesh phasing can effectively suppress several different modal responses, and a physical interpretation of this phenomenon is provided by using the modal equations and the modal analysis results.
查看更多>>摘要：Robot-assisted minimally invasive key-hole surgeries have thrived in recent decades, primarily robotic MPL (Multi-Port Laparoscopy) and SPL (Single Port Laparoscopy). In robotic MPL, surgical manipulators are mainly equipped with straight-stemmed tools with distal wrists. For robotic SPL, when these MPL tools and manipulators are used via a single entry, they often suffer from mutual collisions. On the other hand, dedicated SPL manipulators/tools usually lack adequate payload capabilities due to the slim multi-joint designs. To facilitate SPL, a SORST (Stem-Optimized Robotic Surgical Tool) with a continuum wrist and a kinematically optimized rigid curved stem is proposed. The SORST's curved but rigid stem can help reduce possible collisions and maintain the tool's payload capability. In this curved-stem tool, the tendon tension might be difficult to properly maintain, due to the fact that the tendon may get in contact with the guiding cannula with uncertain friction. Hence, the continuum wrist is introduced for enhancing distal dexterity. Furthermore, an instantaneous inverse kinematics framework is proposed to simultaneously avoid mutual collisions and satisfy the remote-center-of-motion constraint, joint range/velocity limits, and the desired task space twist. Extensive experimental verifications were conducted to demonstrate the efficacy.
查看更多>>摘要：In this study, a gear rattle prediction model that incorporates manufacturing errors such as ec-centricities and tooth indexing errors is proposed. Sets of rattle experiments are performed by using gears of known eccentricities and tooth indexing errors. The model is validated through comparison to these measurements. Experimental and theoretical results show that the gear motions are likely to increase their rattle severity in the presence of such errors. Specifically, tooth indexing errors cause rattling motions to become more prominent and often non-periodic with higher rattle severity indices as use of gears having smaller tooth indexing errors is advis-able for minimizing rattle. Eccentricities are found to result in cyclic variations of the backlash magnitude to cause long-period rattling motions with non-integer average number of coast-side impacts per gear rotation. Further, phasing relationships defining the relative orientations of eccentricity vectors with respect to each other and with the torque fluctuations are shown to be influential in determining whether rattle motions will occur. It is demonstrated that the eccen-tricities of gears can be clocked at a certain angle with respect to each other and torque fluctu-ations to reduce rattling. A new no-rattle criterion is proposed at the end that includes the eccentricity magnitudes and these key phasing relationships.
查看更多>>摘要：Strict underactuation, complex structure, shape variation, and elasticity of machine elements cause many challenges in control of telescopic truck cranes. We develop a dynamic model of telescopic boom cranes considering flexibility and damping of load-carrying rope, viscoelasticity of boom-luff cylinder and extension cylinder. Modeling and control are constituted for the complex operation in which three motors including payload hoist, boom elevation, and boom expansion are simultaneously activated. We provide two observer-based robust controllers entitled second-order and fast-terminal sliding mode controls. These controllers work well even when the crane faces parametric variation and disturbance. The control system halves its sensors because of the performance of observer. We analyze and verify the effectiveness of modeling and controllers by applying to a Grove-TMS500 truck crane. Simulation results show the asymptotical convergence of actuated outputs and the stabilization of unactuated ones. The crane responses hold the robustness against winds and parametric uncertainties. The oscillations of crane outputs are due to elastic components such as handling ropes, two hydraulic cylinders for luffing and expanding the boom. The controllers well eliminate these undesirable oscillations.
NSTL
Elsevier