查看更多>>摘要：The slender rods experience mechanical deformation in most practical cases. The deformation should be modeled numerically since it affects the dynamics of the entire system. This paper models flexible slender-rods in a closed-loop multibody system by considering rods as variablelength constraint equations, and updating the positions and velocities. The principle behind this method is to use the rod-removal technique and the 3D semi-recursive multibody formulation. When applying the rod-removal technique, the rods-associated second-derivative-based inertial forces and velocity-dependent inertial forces and external forces must be calculated and assembled in the whole system. If consider the rod-flexibility, the stiffness equations of the removed flexible-rods, in turn, can be formulated based on beam finite elements. The finite element equations can be combined with the multibody equations of motion to perform the simulation of rigid-flexible multibody system. Two simple multibody systems with a flexible rod are employed to verify the effectiveness of the presented flexible-rod removal technique. A rigid-flexible vehicle model is taken as an example to investigate the effects of flexible-rods towards vehicle dynamics, where different initial velocities, sprung masses, and rod materials are considered. The numerical results describe how the dynamics of multibody systems changes when the deformation of flexible rods is considered. It proves that the effects of rod-flexibility must be taken into account for multibody systems especially in worse cases.
查看更多>>摘要：Parallel robots that incorporate kinematic redundancy in their designs are frequently considered for use in different applications due to their ability to avoid direct kinematic singularities within their workspace. Knowledge of a robot's wrench generation capabilities constitutes essential information when designing its geometry and planning its optimal use to accomplish various tasks. In the presence of kinematic redundancies, the determination of a robot's wrench generation capabilities at a given pose of its mobile platform depends not only on the limits of its actuators but also on the configurations of its legs. In this work, an algorithm allowing for the closed-form computation of the available wrench set of the 3-RPRR planar parallel robot is presented. This results in generating the boundary of the available wrench set as a set of faces in the wrench space. Based on this representation, algorithms allowing for the computation of various application-based performance indices are also described. Example numerical results are included to demonstrate how the tools that are presented could be used in the context of robot design.
查看更多>>摘要：Rolling bearings are one of the important components in wind turbine, whose damage may cause a series of concatenate accidents and even sudden shutdown. For the first time, the effects of center coefficient and weighting coefficient on adaptive chirp mode decomposition (ACMD) performances are investigated via fractional Gaussian noise numerical simulation experiments. Moreover, the new initial parameter guided ACMD method is creatively developed based on the energy distribution entropy fluctuation spectrum strategy and the two stage convenient search strategy. Targeting at the damage identification problem of wind turbine bearing under variable speed condition, a hybrid approach is further proposed by fusing the initial parameter guided ACMD method with the computed order tracking (COT) algorithm. Analysis results of experimental signals and engineering case demonstrate this novel hybrid approach can well identify weak bearing damage, the characteristic extraction ability and the damage identification precise of this approach are better than those of different contrastive methods.
查看更多>>摘要：In this paper, a pure rotation micropositioning stage with dual-range is designed to acquire a large-rotation angle and a high-resolution at the same time. The designed stage consists of a large-range rotation mechanism and a small-range rotation mechanism and it combines nested structure, multi-layer and symmetric structure. Analytical modeling is presented to investigate the kinematic and static characteristics by using the compliance matrix method and pseudorigid-body model. A series of simulations are conducted to demonstrate the effectiveness of the proposed design. The simulation results show that the designed stage has a large-rotation range of [0 mrad, 17.40 mrad] and a small-rotation range of [0 mrad, 0.88 mrad].
查看更多>>摘要：In this paper, a new cable-driven segmented manipulator is studied, which maintains a nearly piecewise constant curvature under the constraint of a cable-constrained synchronous rotating mechanism. The main purpose of this paper is to present a refined dynamics model for the cable-driven segmented manipulator system considering friction effects and deformation of the cables. First, the arbitrary-Lagrangian-Eulerian method is introduced for the modeling of the driving cables, and the friction between the cables and the manipulator is described by the LuGre model. Second, the dynamics model and algorithm for the 2D segmented manipulator system considering friction effects and deformation of the cables is established using Lagrange's equation of the first kind and Baumgarte's stabilization method. Finally, a single-segment manipulator and a multi-segment manipulator are simulated successively, and an example of the manipulator circumventing an obstacle is simulated. The control errors caused by friction and deformation of the cables are analyzed, and the influences of the joint angle and the cable pretightening force on the control errors are discussed. In addition, the control errors of different segments are compared and analyzed, and reduced by adjusting the pre-tightening force of the cables.
Liquan JiangShuting WangYuanlong XieSheng Quan Xie...
25页
查看更多>>摘要：The four-wheel-steering mobile robot (FMR) is widely applied in the manufacturing industry, where accurate and stable lateral motion control is a prerequisite for ensuring manufacturing quality and efficiency. However, serious time-varying perturbations such as system uncertainties and external disturbances usually lead to unsatisfactory control performance. By designing constrained prediction and sliding mode mechanisms, a novel adaptive fractional robust finite time controller is proposed to achieve a system with required control accuracy and stability under serious time-varying perturbations. Compared with existing FMR solutions, the proposed method has the following attractive properties: (1) Without requiring the derivatives of time-varying perturbations, the proposed method utilizes a modified fractional super-twisting sliding mode switching law to guarantee the system robustness of dynamical tracking and disturbance rejection; (2) The differences between the nominal predicted states and the feedback ones can be well accommodated despite unmodeled dynamics and external disturbance; (3) By designing continuous control inputs, the "chattering phenomenon" in conventional control laws is carefully handled. Moreover, sufficient conditions are derived for the variable control gains to ensure the input-to-state practical stability and finite time convergence. Under harsh working conditions, two comparative experiments implemented on a real-life FRM are performed for demonstrative purposes.
查看更多>>摘要：The existing transfer learning-based fault diagnosis methods basically make use of fault knowledge learnt from one source domain to another target domain. Due to variable operating conditions, transfer tasks in the fault diagnosis need be inevitably performed many times, which limit their industrial applicability. To address the problem, a new residual deep subdomain adaptation network is proposed for intelligent fault diagnosis of bearings across multiple domains. Its remarkable advantage is that only one transfer task need be executed no matter how the operating conditions change. In this method, a residual network is constructed to extract transferable features from source domain and target domains. And, local maximum mean discrepancy is introduced to accurately align the distribution of the related subdomains within the same category in the source domain and the target domains. Comprehensive experimental results confirm that the proposed method can make use of fault knowledge learnt from the single source domain for fault diagnosis in the multiple target domains. The classification accuracy has a significant improvement as compared with the existing popular methods.
查看更多>>摘要：This paper provides a geometrical insight into the dualities of compliant mechanisms via repelling screws. A method for the construction of the repelling screw system is proposed. By means of screw theory and linear algebra, the closed-loop relationships among the twist/wrench spaces of both actuation- and constraint-screw systems are identified, upon which the kinematics, statics and stiffness/compliance of both full- and limited-mobility compliant mechanisms are analysed. The internal correlations between repelling screws and dualities of mechanisms are investigated, which reveals both orthogonal and dual properties of mechanisms with either parallel or serial configuration. The repelling-screw-based representation is applied to describing the permitted motions and restricted constraints of the mechanism. In addition, a novel and systematic approach for parallel-to-serial/serial-to-parallel transformation is proposed, which retains the capability of changing the constraints and relative dimensions of the target configuration to better suit a specific task. A few examples conducted demonstrate the feasibility of the proposed approach and the effectiveness of the repelling-screw based interpretations of mechanism geometries.
查看更多>>摘要：A 7 degrees-of-freedom (DOF) humanoid robotic arm is proposed based on the comfort and affinity of human-robot interaction. For the characteristics of the robotic arm with end pose coupling, an integrated approach based on the analytical and reverse order methods is proposed to obtain the closed-form solution of the robotic arm at the position level. The coordinate system establishment method and mapping relationship of the Denavit-Hartenberg (D-H) parameters at positive and reverse order robotic arms are deduced. Subsequently, the analytical solution of the reverse order robotic arm is derived based on the parametrization method, and the feasible range of the arm angle is obtained using the joint limits. Additionally, the novel global arm angle optimization algorithm is proposed to simplify calculation in the intelligent algorithm, and the relationship between the optimization factors and global arm angle is analyzed. Finally, the validity of the methods is verified by the kinematics simulation based on the Robot Operating System (ROS). The simulation results demonstrate that the proposed integrated approach and global arm angle optimization algorithm can effectively solve the closed-form solution of the robotic arm.
查看更多>>摘要：The gear profile grinder is important to ensure the geometric accuracy of tooth surfaces. However, its machining accuracy is significantly reduced by the geometric and thermal errors. So the geometric and thermal errors should be controlled simultaneously. The geometric error modeling and decoupling of the gear profile grinder are studied, and the mapping relationship between the geometric accuracy of tooth surfaces and machine errors is constructed. To establish a robust thermal error model, a physically-based model is established to prove the feasibility of using the bidirectional long short term memory network (Bi-LSTMN) to establish a self-learning error model. The high-frequency noises are filtered and singular values are reduced by the Savitzky- Golay (SG) filtering algorithm. An attention-gate-based Bi-LSTMN (AGBi-LSTMN) is proposed to reduce the time complexity. Then the mixed-variants whale optimization algorithm (MVWOA) is proposed to optimize the hyper-parameters, and SG-MVWOA-AGBi-LSTMN is proposed for the thermal error prediction. Finally, the simultaneous geometric and thermal error control is implemented. The results show that the total tooth profile precision is increased by ISO level 3, and the tooth profile tilt precision is increased by ISO level 5 with the simultaneous geometric and thermal error control.
NSTL
Elsevier