查看更多>>摘要：When limbs of a parallel mechanism have been selected, the geometric relation among limbs determines the mechanism's motion. The limb arrangement which affects the mechanism's motion raises a fundamental and significant issue. If a mechanism only owns limbs with Lie group motions, it is convenient to predict how a limb arrangement determines the mechanism's motion. However, if a mechanism is mainly or purely constituted by limbs with motions of general differential manifolds, it is difficult to find the influence of a limb arrangement. On this regard, this paper provides an in-depth investigation by focusing on motion analysis of parallel mechanisms consisting of three PRS limbs with planar-spherical manifolds. By formulating and comparing the motion characteristics of these mechanisms which though could be modeled difficultly by a mathematical tool without using the finite displacement screw, a finite displacement screw-based group method is proposed in this paper to resolve the raised issue. The novel approach presents results in expressions of new types of manifold motions, providing a foundation for design and application of parallel mechanisms having the various three-planar-spherical manifolds’ intersection motions.
查看更多>>摘要：Cuspidal robots can travel from one inverse kinematic solution to another without meeting a singularity. The name cuspidal was coined based on the existence of a cusp point in the workspace of 3R serial robots. The existence of a cusp point was proved to be a necessary and sufficient condition for orthogonal robots to be cuspidal, but it was not possible to extend this condition to non-orthogonal robots. The goal of this paper is to prove that this condition stands for any generic 3R serial robot. This result would give the designer more flexibility. In the presented work, the geometrical interpretation of the inverse kinematics of 3R robots is revisited and important observations on the nonsingular change of posture are noted. The paper presents a theorem regarding the existence of reduced aspects in any generic 3R serial robot. Based on these observations and on this theorem, we prove that the existence of a cusp point is a necessary and sufficient condition for any 3R generic robot to be cuspidal.
查看更多>>摘要：Sliding-frame mobile robots used for autonomously inspecting metallic structures consist of two bodies connected by few joints. They move by alternately adhering one body to the structure while moving the other body to the next position. Sliding-frame robots are simpler and offer safer adhesion than legged and wheeled robots, and their control can be simplified using binary actuators that adopt only two stable states. However, most existing sliding-frame robots require continuous actuators to reach targets with precision, since binary actuators impose steps of fixed length. To solve this, this paper presents a new sliding-frame robot consisting of two bodies connected through a 2RPR-PR kinematic chain driven by two binary actuators. The 2RPR-PR chain can perform nonsingular transitions, which is the ability of many parallel robots to switch between different poses corresponding to the same state of its actuators, without crossing singularities. Thanks to this, the poses reachable by the proposed robot are doubled, granting it a denser workspace and more accuracy than similar robots, using only two binary actuators. The feasibility of the proposed robot is shown through a prototype.
查看更多>>摘要：Harvesting energy from human motion has the potential to power wearable sensors and low power portable systems. Here, a backpack harvester that generates electrical energy by suspending the pack-mass only on springs is demonstrated. In this mechanism, the relative motion between a fixed frame (relative to the body) and a suspended frame winds a torsional spring that serves as a mechanical reservoir in one-half of the oscillation cycle (one walking step). In the second half cycle, the stored energy is released to the generator. This approach eliminates the damping force from the generator on the human bearing the load. As the load is suspended on springs and does not directly drive the generator, the proposed system results in a decoupled harvester. Experimental results demonstrate that the output power generated from the decoupled harvester is 65% of that obtained from a semi-coupled harvester with 52% smaller backpack displacements and oscillatory forces. The decoupled and semi-coupled backpack harvesters achieved 53% and 45% efficiency at 1.4 m/s walking speed compared to 34% efficiency in a fully coupled harvester. This demonstrates significant advancement towards developing decoupled backpack energy harvesters that suspend pack-mass only on springs.
查看更多>>摘要：This paper presents the design, modeling, optimization, simulation, and experimental study of a new asymmetric flexible microgripper driven by a piezoelectric actuator. By comparing the asymmetric microgripper with the corresponding symmetric one, new guideline is introduced to design the gripper mechanism. The uniqueness of the gripper lies in consistent working mode and first resonant mode shapes without the dense mode of resonance. The proposed asymmetric gripper is composed of a three-stage flexure amplification mechanism, which can achieve friction-free and clearance-free displacement amplification. The gripper adopts the separate design of driving arm and sensing arm to avoid possible interference between them. The key geometric parameters affecting the performance of the flexure hinge are selected and optimized. By resorting to the pseudo-rigid body model, the kinematic, static, and dynamic models of the asymmetric gripper are derived. The working stroke, clamping force, and resonant frequency of the designed monolithic gripper are verified by conducting both simulations and experiments. A variety of experiments on the successful gripping of micro-objects of different sizes and shapes demonstrate its promising use in practical micromanipulation and microassembly applications.
查看更多>>摘要：Due to the characteristic of multi-tooth line contact, toroidal involute (TI) worm drive is characterized by high-loading capacity but sensitive to the assembly errors. This paper proposed a mismatched TI worm drive based on the media gear to reduce the assembly error sensitivity. According to spatial meshing theory, the design method and mathematical model are established. The geometric properties of TI worm flank can be fine-tuned and change the contact characteristics of the worm pair by adjusting the tooth number of media gear. The spatial point-contact analysis method is presented, and the effects of some design parameters on meshing performance are studied. The tooth contact analysis (TCA) is simulated to verify the carrying capacity and error adaptability. These results suggest that the mismatched TI worm pair remains the characteristics of multi-tooth contact and large carrying capacity. Compared with the standard TI worm drive, it has better error adaptability.
查看更多>>摘要：Modeling and simulation of mechatronic systems require a multi-disciplinary approach as several physical domains interact with each other. Due to this heterogeneity, each domain can benefit from a dedicated time integration strategy as well as modeling formalism to control the error in simulation and reduce computational overhead. Current multi-rate adaptive time-stepping approaches disregard the system dynamics knowledge obtained in previous simulations and adapt the time steps at run-time as a black-box model. Although current multi-rate adaptive time-stepping approaches do not exploit the time scale of the physics of each domain, this information can be exploited in co-simulations by having a predefined multi-rate time integration approach in design space exploration and parameter identification applications, which involve repeated simulations with similar dynamics. In this study, an offline adaptive co-simulation technique is introduced. The proposed method adapts the communication and time integration time steps before the simulation using the estimated error data from past co-simulation runs. The offline adaptive co-simulations performed faster against the run-time adaptive co-simulations for comparable accuracy levels in 1D and multi-level mechatronic systems with changing loading and initial conditions.
查看更多>>摘要：A novel structural spectrum synthesis method of the open kinematic chain is presented to reveal the varieties and design nature of the mechanism structural layout. Its novelty lies in that it is able to generate the structural spectrum by the matrix mapping. Starting from the kinematic chain and topological diagram, the association matrix between the links and the kinematic pairs is established. Then, the orientation matrix is proposed to represent the relative position relationship between the adjacent links. By defining Boolean operation rules of the orientation matrixes, the overall orientation matrix can be derived to generate the structural spectrums of the mechanism. Finally, this method is successfully applied to design the structural spectrums of the vertical machining center and the cylindrical coordinate robot. In the future, the proposed method can be generalized to the structural design of all machines, and used as the fundamentals for the following detailed and innovative structural design. The work will pave the way for the digital and automated structural design from the kinematic chain to the mechanism structure.
查看更多>>摘要：The monitoring of overhead contact lines (OCL) is a key part of railway infrastructure maintenance. This paper proposes a methodology to assess the lateral geometry of contact wire, the so-called stagger, by using the dynamic response of a pantograph. The methodology is tested in a validated virtual environment that resembles the behaviour of the pantograph when it interacts with the OCL. A signal processing is developed to define features relating the lateral position of the contact wire with the vertical acceleration of the contact strip. It is demonstrated that these features have a clear and close connection with the lateral position of the contact wire. Subsequently, model-driven machine learning algorithms are defined using these features to address the OCL stagger prediction and the detection of out-of-range lateral displacement due to a faulty steady-arm. The methodology shows a good prediction performance in the estimation of the stagger amplitude/central position and the steady-arms diagnosis. The prediction of the stagger amplitude is performed with a root-mean-square error of 4.7(10)mm. In addition, the area under the Precision–Recall curve is 0.952 CI95 [0.940, 0.962] for the steady-arms diagnosis.
查看更多>>摘要：Tunable waterbomb origami has attracted significant attention for its superior capability in structural reconfiguration, which is utilized to tailor the mechanical properties of metamaterials. Recent researches mainly focus on the kinematic analysis of waterbomb origami folding process to convert the planar crease pattern to a three-dimensional folded configuration. Nevertheless, the inverse problem, i.e., the design of crease patterns based on an arbitrary waterbomb origami configuration, is rarely studied. In the paper, an innovative “seven-crease” waterbomb pattern is proposed by modification of the classic “six-crease” waterbomb crease pattern. The new pattern design avoids the risk of self-penetration during folding process. Recursive algorithm and design constraints of the “seven-crease” waterbomb crease patterns are derived based on the kinematic relationship. The folding feasibility of the proposed crease pattern is validated against the finite element simulations of two sample models, which match well with the theoretical results.
NSTL
Elsevier