查看更多>>摘要：In this article, we present a novel tension distribution algorithm for cable-driven parallel robots (CDPRs) with two degrees of actuation redundancy. The algorithm consists of calculating the tension feasible region (TFR) and optimizing the tension distribution. The TFR has been innovatively calculated without relying on the convex hull method. The topological relationship of the vertices is maintained, so the calculation steps are greatly reduced. For optimizing TFR, various functions are proposed, especially the tension robustness index is defined. We prove the complexity and continuity of the algorithm and we study several examples. The results are compared with those obtained with the existing state-of-the-art method, and the proposed technique is shown to be more computationally efficient. The robustness of the optimal solution is also calculated. The proposed algorithm can be applied in some real-time systems with unmeasurable interference, such as interactive devices.
查看更多>>摘要：High-tech equipment critically relies on flexures for precise manipulation and measurement. Through elastic deformation, flexures offer extreme position repeatability within a limited range of motion in their degrees of freedom, while constraining motion in the degrees of constraint. Topology optimization proves a prospective tool for the design of short-stroke flexures, providing maximum design freedom and allowing for application-specific requirements. Stateof-the-art topology optimization formulations for flexure synthesis are subject to challenges like ease of use, versatility, implementation complexity, and computational cost, leaving a generally accepted formulation absent. This study proposes a novel topology optimization formulation for the synthesis of short-stroke flexures uniquely based on strain energy measures under prescribed displacement scenarios. The resulting self-adjoint optimization problem resembles great similarity to 'classic' compliance minimization and inherits similar implementation simplicity, computational efficiency, and convergence properties. Numerical examples demonstrate the versatility in flexure types and the extendability of additional design requirements. The provided source code encourages the formulation to be explored and applied in academia and industry.
查看更多>>摘要：Compliant Mechanisms (CMs) have been a hot research spot in recent years due to their distinguished mechanism concept from conventional rigid-body mechanisms: CMs can transfer motion, force, and energy only through the deflection of flexible components. Therefore, the accurate and efficient kinetostatic modeling for these elementary flexible components plays a rather important role regarding conducting synthesis of a studied compliant mechanism. In this paper, we have reviewed the commonly-used beam modeling methods in CMs, most of which are essentially dedicated to handling geometrically nonlinear Euler-Bernoulli beam theory. Mathematically speaking, this beam model is essentially a boundary value problem (BVP) of an ordinary differential equation (ODE). We then introduced certain commonly used numerical methods for BVPs to solve the problem where straight beams and circular initially curved beams (ICBs) are studied as two example cases. We have also demonstrated the detailed derivation of these methods and the numerical results along with the corresponding insights on them as well. Besides, we have modeled 2 representative revolute mechanisms (straight-beam-based cross-axis compliant revolute joint and circular-beam-based compliant revolute joint) to prove the feasibility of synthesizing CMs using these numerical methods. Error analysis is presented thereafter, which also confirms the effectiveness of these numerical methods.
查看更多>>摘要：In this research, the design of general hybrid thruster cable-driven parallel robots (TCDPRs) is studied. TCDPRs combine the actuation advantages of both cables and thrusters(rotors) in order to achieve a larger payload capacity and workspace. The additional forces provided by the thrusters can efficiently increase the available wrench set (AWS), and hence the wrench feasible workspace (WFW), compared with pure CDPRs. The focus of this work is to study the arrangement of thrusters such that the TCDPR can produce the desired wrench set over a required workspace. The arrangement refers the number, attachment locations, directions and maximum force of the thrusters. By comparing the WFW of both planar and spatial CDPRs with TCDPRs designed using the proposed methods, it is shown that the AWS and hence the WFW can be increased to meet the requirements. Furthermore, the contributions of the thruster force to decrease the maximum required cable forces is also shown in this work. These show that a well-designed thruster arrangement is an effective approach to increasing the CDPR capabilities.
查看更多>>摘要：In view of the demands for medical imaging compatibility and efficient space occupation around the surgical site, this paper proposes remote center of motion (RCM) parallel mechanisms (PMs) with a passive limb to enable more flexible arrangement of the limbs and actuators in a RCM surgical manipulator. A type synthesis method is proposed to design the 2R1T RCM PMs with a passive limb based on the Lie group. The motion requirements for the RCM mechanism are first expressed in the form of Lie group. The motion arrangement and kinematic structure development are then implemented to obtain the active and passive limbs. By means of this approach, numerous 2R1T RCM PMs with a passive limb are synthesized. The actuated joints are then selected, and a few qualitative evaluation indices are proposed. Finally, the motion configurations of two generated mechanisms are validated through simulation. The proposed method is universally effective for the type synthesis of multi-degree of freedom RCM PMs with a passive limb.
查看更多>>摘要：Electro-mechanical actuators including planetary roller screw (PRS) support cyclic loads in aeronautical conditions. PRS multiple thread contacts between screw, rollers and nut allow the mechanism to support large loads. However, aeronautical accreditation requires fine prediction of fatigue lifespan. In this paper, a fatigue design strategy for PRS mechanisms is proposed combining Hertz contact model and a multi-axial fatigue criterion. The method is applied on two examples, one standard and one inverted PRS.The lifespan of PRS mechanism depends on maximal Dang Van stress. The Hertz sliding angle (Hertz contact main direction/sliding velocity) was introduced to analyze PRS performances. For both examples, the maximum stress at thread contact were located in bulk material but not at the surface. Dang Van stress mainly depended on curvature ratio, Hertz sliding angle and loads. Based on this analysis, Dang Van criterion was implemented to derive the loading domain of infinite lifespan of the mechanism. Critical contact was not always on the roller-screw side.
查看更多>>摘要：This paper presents a design approach for gravity compensators using planar four-bar mechanisms and a linear spring. This work enables the development of a class of gravity compensators encompassing 42 different types, which are characterized by high performance and kinematic simplicity. The gravity compensators are constructed by combining planar four-bar mechanisms with a rotating mass and attaching a linear spring to each mechanism, then permuting the springs. The parameters of the gravity compensators are derived from an optimization procedure that minimizes the actuator torque within a specified balancing zone. The performances of the gravity compensators were demonstrated via both numerical examples and experiments. The results showed their design feasibilities and high performances in which a torque reduction rate of 87.8% was practically achieved. Lastly, an application of the proposed gravity compensators to serial robots is described. It was found that the actuator torque of a serial robot over a prescribed workspace could theoretically be reduced by 98.2%. A prototype of a serial robot was also built to validate the applicability of the gravity compensators.
查看更多>>摘要：Most of the existing gear fault diagnosis methods only use the single-channel signal for processing. In order to extract more fault information and realize more comprehensive and accurate fault analysis, it is necessary to process the collected multi-channel signals. In this paper, a novel multivariate signal decomposition method, multivariate local characteristic-scale decomposition (MLCD) is proposed to decomposes multi-channel signal simultaneously. Comparing MLCD with multivariate empirical mode decomposition (MEMD), the results show that both methods are suitable for multivariate signal decomposition, but MLCD is superior to MEMD in computational efficiency, suppression of endpoint effect and decomposition accuracy. In order to highlight gear fault characteristic frequency, 1.5-dimensional empirical envelope spectrum (1.5D EES) is proposed. 1.5D EES combines the advantages of empirical envelope method and 1.5-dimensional spectrum, which can effectively reduce the noise of envelope signal and highlight the fault characteristics of signal. Based on the above two methods, a new gear fault diagnosis method, multivariate local characteristic-scale decomposition and 1.5-dimentional empirical envelope spectrum (MLCD-1.5D EES) is proposed and applied to multi-channel gear fault signal decomposition and fault feature extraction. Simulation and experimental results demonstrate the effectiveness and superiority of MLCD-1.5D EES.
查看更多>>摘要：This paper deals with centroid alignment for the spaceflight vehicles that work on orbit under microgravity environment, due to the unavailability of centroid measurement on ground, which is based on the principle of mass-radius products in different configurations of static equilibrium. A physical prototype of articulated mechanism for centroid alignment, consisting of three sets of linear modules with moving mass mounted, was developed and experimentally validated. The variational method was adopted to derive the error model for accuracy and sensitivity analysis of the developed articulated mechanism with the consideration of parameter uncertainties, from which it is found that the centroid position of the whole system is much more sensitive to the angular parameter variations than the linear ones. With the developed error model, an iterative approach of centroid alignment to ensure the centroid offset to meet the requirement is proposed, regardless of whether the parameter variations can be ignored, and numerous simulations verify the efficiency of the proposed approach.
查看更多>>摘要：Passive prosthetic feet struggle to reproduce the human biological ankle range of motion and push-off. We propose the Hybrid-Hydraulic Ankle Prosthesis (H2AP), a prosthetic foot that provides a greater range of motion and push-off support compared to regular carbon feet. This novel prosthesis comprises a carbon foot and a hydraulic unit that includes a plantar flexion damper, a dorsiflexion damper, and a unidirectional spring that engage at specific phases of the gait cycle. The dampers are designed to enable an increased range of motion, and the unidirectional spring is used to store and release increased energy in late dorsiflexion and push-off. This paper focuses on the details of the mechanical design of the H2AP, its working principles, and the parameter tuning process. The design target is to replicate human ankle behavior in unimpaired walking, which is optimized using mathematical analyses and a simulation model. Pilot walking experiments with one transtibial amputee subject on level ground and a treadmill demonstrate the usability of the developed device and its acceptance in providing the intended functionality. The proposed design methodology can be used in the development and parameterization of the other assistive devices.
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Elsevier