Mechanism and Machine Theory最新文献

Small offshore platforms rock and heave under the impact of waves. The adaptive landing gear should reduce the impact force between the landing legs and the platform while keeping the unmanned aerial vehicle (UAV) level. In this paper, a general virtual parallel model is proposed to describe the coupling relationship between multi-legged landing gear and the platform during buffer landing. Based on Lie group theory, a method of constructing various types of landing gear as a virtual parallel model is proposed. The landing gear base, the legs and the ground can be established as a unified parallel mechanism. Based on the virtual parallel model, the landing stiffness is established to evaluate the buffering performance of the landing gear in the pre-landing posture. A buffer landing surface which can make the landing gear obtain superior buffering effect can be obtained in the workspace through the case analysis. A buffer landing strategy based on virtual parallel model is established. The feasibility and effectiveness of the control strategy is verified by simulations and prototype experiments.

This paper addresses the algebraic synthesis of novel single-loop 6R spatial mechanisms, enabling constant -1:1 or 1:1 velocity ratio transmission between two adjacent axes, whether parallel, intersecting, or skew. Based on the motion polynomial over dual quaternions, an algebraic synthesis method including four steps is presented to construct and optimize single-loop 6R spatial mechanisms with a constant transmission ratio of -1:1 or 1:1 between arbitrarily designated input and output axes. Using this method, several novel single-loop 6R spatial mechanisms for constant velocity transmission are constructed by designating different poses and rotation directions of the input and output axes. Kinematics analysis of single-loop 6R spatial mechanisms is implemented to verify their transmission characteristics. The results reveal that the generated 1-DOF single-loop 6R novel mechanisms can indeed transmit motion with a constant transmission ratio of -1:1 or 1:1 between two adjacent parallel, intersecting, or skew axes. This work provides a framework for further investigation on single-loop mechanisms with special transmission characteristics.

Deployable mechanisms play an increasingly crucial role in aerospace, yet their design still faces challenges: 1) The folded height increases while its deployed height decreases, which is not conducive to improving the folding performance; 2) Compared with revolute joints, prismatic joints have relatively weak reliability in complex space environments. To address the above challenges, novel constant-height deployable mechanisms with only revolute joints are proposed in this paper. The deployable mechanisms exhibit one degree of freedom, enabling them to attain modular expansion. Subsequently, the mobility properties of these deployable mechanisms are substantiated through screw theory. Assembly strategies for constant-height deployable mechanisms are proposed, and deployable ring trusses are further constructed to provide support structures for satellite mesh reflector antennas. The kinematics are analyzed to investigate the deployable characteristics of the proposed deployable mechanisms and ring trusses. The prototypes of a deployable mechanism and a ring truss are established to validate the designed deployable mechanisms. This work contributes novel types of deployable mechanisms with potential advantages, aiming to function as valuable references for the design and analysis of deployable trusses.

The gearbox vibration signal of a planetary gear set contains multiple components caused by different excitations. Separating the gearbox vibration signal to decouple its components can provide core information for operational status monitoring. In this paper, we propose an indirect gearbox vibration signal separation method based on parameter identification. A novel vibration signal model is established using the modal shape of ring gear. A parameter identification method is adopted to determine the parameters of the vibration signal model. The vibration signal components are reconstructed based on the vibration signal model and identified parameters. To evaluate the performance of the proposed method, a ring gear response calculation method derived from the elastic theory of ring gear is presented. The influences of unequal load sharing and meshing position errors on vibration signals are studied through numerical simulations using the calculation method. Experiments are conducted in a planetary gear set test rig. Comparisons between the experimental results obtained by the separation and calculation methods indicate the effectiveness of the proposed separation method.

This paper proposes a novel underwater rotorcraft vehicle with a passively adjustable configuration based on a universal joint (URV-PAU), which addresses the issue of increased propeller load and control stability caused by the rigid structure of existing vehicles when tilted. Compared with designs that do not incorporate a U-joint structure, this vehicle can reduce energy consumption and enhance system manoeuvrability. First, a kinematic and dynamic model of the URV-PAU is established based on its configuration. Considering the nonlinearity of the system, the modelling errors of the dynamic model, and external disturbances, an adaptive backstepping sliding mode controller(ABSSMC) is designed to achieve motion control in proximity to the seabed. A prototype of the underwater rotorcraft vehicle was constructed according to the principles of modular design. Subsequently, underwater trajectory experiments were carried out within a water tank. The experiments demonstrated that the URV-PAU results in a reduction of approximately 10 % in system energy consumption and an improvement in system manoeuvrability compared with designs without a U-joint structure during motion at a constant depth.

In this paper, we perform the design optimization and comparison of two tensegrity-inspired manipulators, composed of two anti-parallelogram (X) joints and two revolute (R) joints, respectively. These manipulators are equipped with springs and are actuated remotely with four cables each. In our recent article (Muralidharan et al., 2024), the conditions for the mechanical feasibility of springs and bars have been discussed for the two manipulators, followed by the computation of their stable wrench-feasible workspace (SWFW). Building on that work, in the proposed paper, we design the 2-X and 2-R manipulators to carry a given point mass payload over a disk of a specified radius while minimizing their maximal actuation force, moving mass, and size. We present the Pareto optimal fronts for the two manipulators and compare several designs from them. Then, we study the variation of the chosen objectives for different payload and disk radius specifications for the two manipulators to determine which one is better under what circumstances. Finally, we illustrate that the proposed optimization scheme can also be applied to other design scenarios with minimal changes.

This study proposes a novel calculation method for meshing clearance between two mating screw rotors in compressors and vacuum pumps. The meshing clearance is obtained by calculating the minimum distance between the helix curves and the rotor surface. The 3D contact points of the screw rotor pair are found by applying the proposed algorithm. In particular, this method is robust enough to precisely calculate the clearance for the rotor type with several singular points where the shortest distance direction misaligns with the normal direction of the rotor surface. As demonstrated in the numerical examples, the proposed method is possible to estimate the clearance between two mating screw rotors with constant or variable pitch, as well as feasible to analyze the meshing clearance between two unconjugated rotors. In addition, differences in the clearance distribution of a variable-pitch screw pair with yaw and pitch misalignments are predictable. These results validate the robustness and flexibility of the proposed method.

We introduce visualization-based methods to analyze and synthesize interconnected hybrid (ICH) systems. These systems consist of joints that are not strictly parallel nor serial to one another. We include two types of analysis methods – one that uses joint freedom spaces and another that uses joint constraint spaces. These methods leverage intuition to determine the mobility, under-constraint, over-constraint, transmission, and load paths of any mechanism. The analysis methods are an interpretation of previously established numerical approaches for ICH systems. To adapt the complexities of screw theory and matrix algebra, this work builds off the geometries and systematic rules of the Freedom and Constraint Topologies (FACT) design approach. The synthesis approach is a reversal of the freedom-based analysis method. This synthesis approach takes a designer from any set of desired transmissions to an ICH system capable of achieving them. Both the analysis and synthesis approaches are accompanied by an example compliant mechanism to illustrate their utility and limitations. These methods seek to facilitate the design of emerging mechanism classes, such as metamaterials, and extend the FACT design approach to include ICH systems.

This paper introduces the concept of Generalized Compliance for continuum robots, specifically for those modeled with the Cosserat Rod theory. Unlike existing models based on tip compliance, the proposed approach considers interactions along the entire body of the flexible robot. The paper also presents a novel method referred to as the Low-Level Derivative Propagation Method, which is designed for the computationally efficient derivation of the Generalized Compliance matrix. The proposed method streamlines calculations and reduces integration time. The presented method, which is general and applies to various types of continuum robot models, is demonstrated on the case of a Concentric Tubes Continuum Robot. We provide detailed derivations of the equations and computation techniques leading to the derivation of the Generalized Compliance matrix, as well as a large-scale numerical validation of the method. The code used in this paper is available on the following GitHub website: https://github.com/benoitrosa/Generalized-Compliance-Computation-for-Continuum-Robots.

Instantaneous pole axes (IPAs) fully describe instantaneous kinematics of spherical mechanisms. In single-degree-of-freedom (single-DOF) mechanisms, IPAs’ locations uniquely depend on the mechanism configuration. Such a property allows the deduction of instantaneous-motion characteristics by means of analytic techniques based on geometric features of the mechanism configuration. Moreover, these geometric/analytic approaches are extendable to mechanism's static analyses since the virtual work principle relates mechanism's statics to its instantaneous kinematics. Analytic approaches based on geometric reasoning are of interest in mechanism design and their further extension to dynamic analyses is appealing in that context. This work proposes a possible extension of IPA-based techniques to dynamic analyses of single-DOF spherical mechanisms by using Eksergian's equation. A novel general dynamic model for single-DOF spherical mechanisms is proposed, which is based on IPAs’ locations. Then, the effectiveness of the proposed model is applied to a relevant single-DOF spherical mechanism.