查看更多>>摘要：The ancient European mechanical clock with automata is one of the indicators of manufacturing technology, and the clocks exported to Asia offer evidence of cultural exchange at that time. The Gilded Copper Rising and Falling Pavilion Clock Inlaid with Gemstones is one of the ingenious mechanical work made in Britain and exported to China in the 18th century. Although it's well preserved in the Forbidden City in Beijing (Palace Museum currently), the internal mechanical structure is not open to the public, because of its historical value. In order to reconstruct the pagoda automaton attached to the clock, structural analysis is presented according to the text records of the other four clocks with similar automata. A systematic design approach is proposed herein. The feasible mechanisms are synthesized by going through generalization, specialization, and particularization. As the result, nine, three, and four feasible mechanisms with linkage, gear, and cam are generated, respectively. One of the feasible designs with the largest output motion range is selected, and dimensional synthesis is made to achieve the motion characteristics. Its performance is verified through prototype testing.
查看更多>>摘要：In this paper, a design method of double-circular-arc tooth profile for harmonic gear based on curve mapping and bidirectional conjugation is proposed. By considering the kinematic principle of harmonic drive, the curve mapping is used to solve the addendum circular arc, and on this basis, the dedendum circular arc is solved by the bidirectional conjugation. The influence of design parameters on the tooth profile shape and meshing characteristics of harmonic gear drive are analyzed. The results show that the proposed tooth profile design method can not only construct the mathematical relationship between basic parameters (modulus, number of teeth, deformation, etc.) and tooth profile shape, but also realize the multi-tooth engagement of harmonic drive. The change of the scaling coefficient has a great effect on the tooth profile shape. The increase of flexure coefficient will reduce the pressure angle of the tooth profile, and the smaller flexure coefficient is beneficial to reduce the maximum Von-Mises stress of the flexspline during assembly and loading stage. The research results will provide a novel design method for the tooth profile and improving meshing characteristics of harmonic gear.
查看更多>>摘要：The sensor-perceived vibration signals of multistage wind turbine gearboxes have more complex frequency features than that of single-stage gearboxes since there are more meshing vibration sources and more complicated transmission paths inside them, which lead to difficulties in condition monitoring and fault diagnosis. Aiming to understand the vibration frequency features of multistage wind turbine gearboxes, a mathematical vibration model of healthy wind turbine gearboxes is developed and the spectral structure of the model is deduced by adopting Fourier series analysis. In the vibration model, the time-varying transmission paths from all the meshing vibration sources to the fixed sensor are considered, and the equivalent transmission path functions of the time-varying transmission paths are proposed for the first time. The theoretical derivations are validated by both simulations and engineering tests using two cases of 2.0MW industrial wind turbine gearboxes. The findings in this work are not only applicable to the gearboxes studied in this paper, but also to other similar multistage gearboxes, which can provide a priori spectral structure for the multistage gearbox to assist its condition monitoring and fault diagnosis.
查看更多>>摘要：This study proposes a new class of controllers for mobile manipulators subject to both undesirable forces exerted on the end-effector and unknown friction forces coming from joints directly driven by the actuators as well as undesirable forces resulting from the kinematic singularities appearing on the mechanism trajectory. Based on the suitably defined task space non-singular terminal sliding manifold (TSM) and the Lyapunov stability theory, we derive a class of estimated extended transposed Jacobian controllers which seem to be effective in counteracting the unstructured forces. Due to a redundant nature of the tasks to be accomplished, our controllers also a involve useful criterion function (energy consumption) in optimally tracking a desired trajectory. Moreover, in order to eliminate (or to alleviate) undesirable chattering effects the proposed control laws include second order sliding techniques. The numerical computations, which are carried out for a mobile manipulator consisting of a platform of (2, 0) type and a holonomic manipulator of two revolute kinematic pairs, illustrate the performance of the proposed controllers and simultaneously their minimizing properties. Numerical comparison with other control algorithms well-known in the literature is also given.
查看更多>>摘要：There are hundreds of parallel robot designs, of these, some are suitable for fast material transfer operations, others for precision positioning, or like Fanuc's hexapod, for withstanding heavy payloads. Unfortunately, few machining applications using hexapods exist today in the industry due to the complexity and scarcity of practical studies on the kinematic and dynamic properties of these robots. In this paper, kinematic and parameterized finite element models of Fanuc's F-200iB hexapod for robotic machining are presented. First, the complete inverse kinematic analysis of the hexapod is introduced. Using key points' locations from the inverse kinematics, a parametrized geometrical model of the hexapod is developed. Then, the finite element model of the robot is created by assembling all the members with their geometry, mass distribution, material characteristics, and by applying rigorous boundary and joint conditions. Finally, the experimental results show that the parameterized finite element model precisely predicts mode shapes and natural frequencies for several poses of the mobile platform. The accurate simulation model will be essential for optimizing the performance of the hexapod for machining tasks.
查看更多>>摘要：The kinematic synthesis of higher-order path generator mechanisms is herein addressed. Assuming mechanisms in a symmetric configuration, a coupler path sharing up to eight infinitesimally separated points with the ideal curve can be achieved. The novel design methodology is based on "Path-Constrained Points"(PCPs) for the characterization of the coupler motion. In particular, given the higher-order curvature features of the curve to be mechanically approximated, the mechanism link length ratios are analytically computed. The PCPs approach has been herein developed for the four-bar and the swinging-block linkages, but can be extended to a wide class of mechanisms. To speed-up computations, design charts solutions have been also prepared. Finally, the numerical examples and the coupler path plots allow to evaluate the accuracy of the proposed procedure.
查看更多>>摘要：Parallelogram-based remote center-of-motion (RCM) mechanisms have been intensively deployed in intraocular surgical robots. However, the actuation of instrument linear movement in conventional parallelogram-based RCM mechanisms is mostly done by a linear actuator installed near the end-effector. This design inevitably increases the volume and mass on the patient side of the robot. In this work, we present a novel parallelogram-based RCM mechanism that allows distally-actuated instrument insertion and retraction. Compared to the existing work, the proposed mechanism decouples the translational motion from other rotational degrees of freedom with a simple design. This feature may further enhance the safety of delicate procedures like sub-retinal injection. Based on the kinematic analysis, a method is developed for assembly error estimation and correction. Moreover, an automatic instrument changer is integrated with the robotic manipulator. Experiments are conducted on a prototypical system to validate the feasibility of the proposed design. The RCM precision is shown as better than 0.5 mm. The time required for switching surgical instruments is demonstrated as less than 10 s.
查看更多>>摘要：This paper focuses on a novel backlash-adjustable worm drive, and it is composed of a dual-lead involute cylindrical (DIC) worm and an involute helical beveloid (IHB) gear. It is characterized by the low error sensitivity, easy to manufacture and with the backlash-adjustable. The design criteria for the novel worm drive are presented based on a variable-lead and variable-thickness media rack. Then the mathematical model and meshing performance analysis model are deduced and established, and the theory of backlash-adjustable is proposed. The tooth contact analysis (TCA) is conducted by the numerical calculation and stress analysis. Moreover, the experimental gearbox is manufactured, and the contact tests and transmission accuracy tests are completed. These results indicate that the novel worm drive can effectively adjust backlash without affecting the transmission accuracy. This theoretical research provides the theoretical support for further analysis and application of the novel backlash-adjustable worm drive.
查看更多>>摘要：Parallel manipulators, also called parallel kinematics machines (PKM), enable robotic solutions for highly dynamic handling and machining applications. The safe and accurate design and control necessitates high-fidelity dynamics models. Such modeling approaches have already been presented for PKM with simple limbs (i.e. each limb is a serial kinematic chain). A systematic modeling approach for PKM with complex limbs (i.e. limbs that possess kinematic loops) was not yet proposed despite the fact that many successful PKM comprise complex limbs. This paper presents a systematic modular approach to the kinematics and dynamics modeling of PKM with complex limbs that are built as serial arrangement of closed loops. The latter are referred to as hybrid limbs, and can be found in almost all PKM with complex limbs, such as the Delta robot. The proposed method generalizes the formulation for PKM with simple limbs by means of local resolution of loop constraints, which is known as constraint embedding in multibody dynamics. The constituent elements of the method are the kinematic and dynamic equations of motions (EOM), and the inverse kinematics solution of the limbs, i.e. the relation of platform motion and the motion of the limbs. While the approach is conceptually independent of the used kinematics and dynamics formulation, a Lie group formulation is employed for deriving the EOM. The frame invariance of the Lie group formulation is used for devising a modular modeling method where the EOM of a representative limb are used to derived the EOM of the limbs of a particular PKM. The PKM topology is exploited in a parallel computation scheme that shall allow for computationally efficient distributed evaluation of the overall EOM of the PKM. Finally, the method is applied to the IRSBot-2 and a 3RR[2RR]R Delta robot, which is presented in detail.
Thanh, Nguyen CongWalker, Paul D.Zhou, ShileiNong, Zhang...
18页
查看更多>>摘要：This paper aims to fully exploit the superior advantages in improving energy economy and dynamic performance of an electric vehicle powertrain equipped with two motors and multi-gear ratios. Considering the dependence of gear ratio selection on motor sizing, a two-loop optimization algorithm, combined by the global search method and non-dominated sorting genetic algorithm-II, is proposed to find optimal motor sizes and transmission ratios. An energy management strategy with novel shift schedules based on the equivalent efficiency of two motors, current engaged gears, and driving conditions is then recommended. The energy management strategy also optimizes the torque allocation to two motors to minimize electricity consumption. Subject to the total of motor peak powers being constant, simulation results for a case study of urban bus show that the optimization of both motor sizes and gear ratios considerably enhances the energy efficiency of powertrain system. In comparison with a single-motor powertrain, optimal motor scales of larger than 0.42 and corresponding gear ratios reduce the electricity consumption significantly by 4.82-5.08%. Besides, the introduced energy management strategy with optimal shift schedules is proved to ensure comparably maximum efficiency while effectively preventing unnecessary and repeated gear changes.
NSTL
Elsevier