查看更多>>摘要：In order to improve geometric accuracy and loaded contact fatigue life on tooth surface carburizing, an innovative optimization model is established for spiral bevel gears. First, finite element method (FEM)-based tooth surface carburizing simulation is performed. Where, the output carbon content and hardness gradient are used to determine the S-N curve of the given material 20MnCr5 steel. The output residual stress is integrated into the bending stress solution. The output carburizing surface deformation is introduced into the composite surface geometric accuracy. Second, loaded contact fatigue assessment is performed by FEM-based loaded contact stress and S-N curve. Where, loaded contact stress considering residual stress is determined by simulated loaded tooth contact analysis (SLTCA). Third, loaded contact fatigue life-oriented carburizing surface optimization model is established. In this modeling, the composite surface geometric error including carburizing deformation, loaded contact deformation and the prescribed ease-off is used to reflect manufacturing geometric accuracy. Moreover, the limit fatigue life at dangerous point is used a standard to determine the target surface. A sensitivity analysis strategy-based optimization strategy is developed. The proposed method can effectively improve the process parameter modification strategy by considering the collaborative optimization on geometric accuracy and loaded contact fatigue life. Moreover, it also can provide new technical for the current co-design and manufacture of spiral bevel gears.
查看更多>>摘要：Lost motion is a key accuracy index of precision bi-directional gear drive. For planetary gear train (PGT), lost motion behavior is complex due to the coupling effects of multi-planet gears. In this paper, a new bi-directional drive (BDD) model of PGT is proposed considering the coupling effects of multi-planet gears and errors. With the BDD model, the generation mechanism and abatement behavior of lost motion with multi-planet gears are revealed, and a generalized formula of lost motion for PGT with different input components is derived from the lag in movement yielded by meshing clearance. The relationship between meshing clearance and manufacturing errors is determined by the vector loop equations. The effects of errors and manufacturing accuracy on lost motion behavior are analyzed. The eccentricity phase of planet gears on lost motion behavior is investigated through deterministic and statistical analysis, and a strategy of in-phase eccentricity arrangement is suggested for reducing the maximum lost motion. The lost motion test of an actual PGT is conducted. The results well agree with the simulations’, which validates the proposed BDD model and reduction strategy.
查看更多>>摘要：Due to the nondestructive characteristic, the non-contact underwater samplers become important equipment in underwater organism research. This paper proposes a novel underwater sampler with one degree-of-freedom (DOF) deploying-encircling motion based on non-Euclidean rigid origami, and its key factor is the encircling surface origami pattern. The sampler can be deployed and encircle the object gradually from the flat and open configuration to the closed configuration forming an approximate prismatic cavity, and capture organisms without damage. Based on the kinematics of two basic non-Euclidean 4-vertices used in the sampler, the rigid foldability and bifurcation behavior of the origami pattern are analyzed. The bifurcated paths are introduced into the motion transmission path analysis, ensuring the validity of the rigid foldability in all cases. After the bifurcation analysis, the inputs of the pattern are determined. Several performance indexes are evaluated to determine the key parameter. Finally, the drive of the sampler is designed, and the prototype of the sampler is presented and tested for capturing performance in an aquarium.
查看更多>>摘要：In 2021, members of the Mechanism and Machine Theory journal's Editorial Board and many independent reviewers contributed their time and expertise in reviewing manuscripts. This process greatly benefits our editors, contributing authors, and ultimately our readers. In fact, the high standard and reputation of the journal is strongly shaped by the expert knowledge, generous time contribution, and commitment to mechanism and machine science of the body of reviewers. Both, Elsevier, the publisher, and the editor-in-chief of the journal, would like to publicly pay tribute to all of the 1204 reviewers who completed a total of 3769 reviews during the year of 2021. We are extremely grateful for their outstanding contributions and we are look forward to working with them in 2022!
查看更多>>摘要：This paper deals with the stability of loaded gear pairs, considering the effects of tooth profile modification. An analytical method to predict the stability of gear pairs has been developed by transforming their equations of motion to a form similar to the Mathieu equation and employing Floquet theory. The variation of (spur gear pair) teeth meshing stiffness due to tooth profile modification has been introduced, for different amounts of transmitted torque. Stability charts are obtained for different gear pairs, as well as undamped and damped conditions. The simulation results have shown that during operation, the examined gear pairs may cross regimes of unstable behaviour, thus contributing to aggressive oscillations of the gearbox. A holistic transmission design must take the above potential effects into consideration when predicting the durability of machine elements, such as gears and bearings.
查看更多>>摘要：Benefit from the elastic element in the drivetrain, the variable stiffness actuators offer advantages over traditional rigid actuators in security, robustness, energy consumption. However, it is also very bulky due to the integration of the elastic element, especially with large deflection and high load. This article introduces a novel planar high-compliance joint, in which the torsion spring is not an independent part but a synergy result of two adjacent parts developed from the stiffness adjustment linkage mechanism. The flexible element is a cantilever leaf feature belongs to the rigid-flexible integral linkage. The deflection and load ability of the torsion spring can be enhanced by arranging multiple uniform stress leaf branches on the integral linkage without increasing the size. Explicit analytical formulas are derived in a form convenient for leaf parameters design and verified by the finite element simulation and prototype experiments. Finally, the error factors are quantitatively analyzed, which can provide information for the leaf correction design. This kind of planar high-compliance joint is expected to be an ideal choice for the variable stiffness actuators that require stringent axial compactness with large deflection and high load.
查看更多>>摘要：The demand of accurate and real-time dynamics model has recently become critical for implementing effective vibration control in vehicles. The multibody dynamics method provides an appealing alternative for accurate modelling of closed-loop vehicles. In this work, vibration-suppression strategies for a vehicle traversing a bumpy road are proposed, which use a semi-recursive multibody model and a series of control algorithms. First, a 17-degree-of-freedom vehicle is modelled using a semi-recursive multibody method to perform real-time simulation. The vehicle multibody model is verified by using the results from a commercial software package. Second, the PID, fuzzy, and optimal control algorithms are tailored using the obtained vehicle states for vibration suppression. By applying different initial speeds and driving torques, the simulations of the vehicle traversing the bumpy road are performed. The results show that the controllers effectively suppress the vehicle's vibration, and the optimal controller has the best performance. Furthermore, the effect of mass uncertainty on vibration-suppression is discussed. Numerical experiments are performed to verify the effectiveness of the optimal control strategy. The vibration-suppression method based on the vehicle multibody model and the optimal control algorithm can be used to improve the ride comfort in worse road conditions.
查看更多>>摘要：Gear crack evolution is a complex process; therefore, fault diagnosis and monitoring can help to avoid catastrophic accidents. In view of the deficiency that the simple linear plane assumption is made in the conventional crack model, the 3D spatial varying crack evolution (propagating in the depth, tooth width and tooth profile directions simultaneously) is investigated based on the linear elastic fracture mechanics in this study. The acquired crack morphology is used to analyse the time-varying meshing stiffness variation. Then, a system level rigid-flexible coupling model consisting of a housing, gear, shaft, and bearing is utilized to predict the dynamic response, and the theoretical results are compared with the experimental results. Furthermore, crack evolution-induced vibration detection is carried out by the proposed model, and the frequency spectrum characteristic, statistical indicator and instantaneous energy are obtained. The results reveal that the vibration impact is less obvious at the initial stage of crack evolution, but the instantaneous energy can amplify and capture the fault feature. Decreasing the housing stiffness can decrease the vibration impact induced by crack evolution; nevertheless, it increases the difficulty of crack detection.
查看更多>>摘要：This paper presents a general framework for the planning of point-to-point motions that extend beyond the static workspace of six-degree-of-freedom cable-suspended parallel mechanisms. The proposed translational trajectories are based on a generalization of the hypocycloidal motion previously introduced for cable-suspended robots. Also, the concept of ideal kinematic state is used to maximize the chances of obtaining feasible trajectories, i.e., trajectories in which tension is maintained in the cables. The rotational component of the trajectories is based on the use of spherical linear interpolation. A novel formulation is proposed to connect two arbitrary orientations through oscillations going through the reference orientation. It is shown that the impact of the translational trajectories on the tension constraints is largely dominant, compared to that of the rotational trajectories. A procedure is presented for the determination of the trajectory parameters in order to ensure the continuity of the trajectories. Trajectory feasibility is verified, including mechanical interferences and singularity detection. Finally, a natural cylindrical coordinate frame is proposed that yields a very intuitive description of the trajectories and simulation results are given to illustrate the effectiveness of the proposed approach.
查看更多>>摘要：Bionic manipulators are biologically inspired robots with high-level of dexterity. Modeling and control of a bionic manipulator is a challenging task due to number of redundancies present in the system. The applications of bionic manipulators are found in material transport, pick and place operations. Their application is also explored in areas of skeletal trauma treatment, endoscopy and minimally invasive surgery and inspection. This paper presents a detailed bond graph model of a three-dimensional multi-section bionic manipulator which is modeled as a hybrid manipulator, i.e., a serial manipulator whose links/segments are formed by a parallel manipulator. The base of the mobile manipulator as well as the rotational motion of end-effector have been modeled. The developed bond graph model is validated with MappleSim software. Further a model-based control scheme is developed for the bionic manipulator. The control scheme uses the inverse dynamics of manipulator segments to calculate the command torque components required for trajectory tracking. Proportional-Integral-Derivative (PID) controllers are then used along with the model-based controller for accurate trajectory tracking. The control performance is studied through simulation and animation results of the bionic manipulator. To validate the modeling, an example of bionic manipulator Robotino XT has been considered.
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