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  • 1.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kuznetsov, Evgeny
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings2013In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 64, p. 80-92Article in journal (Refereed)
    Abstract [en]

    Dynamic behaviour of compliant cylindrical journal bearings is investigated using linear and nonlinear numerical approaches. Journal motion orbits based on linearized dynamic coefficients are compared to the journal trajectories obtained by the nonlinear transient analysis. Obtained results are presented in terms of orbit amplitude, shape and location. The influence of compliant liner thickness, viscoelastic properties and deformation model is also investigated. A linear model is found to deliver acceptable results at a relatively small shaft unbalance under low to average loads. However, with a journal amplitude motion greater than 37% of the bearing diametral clearance, the linear model should not be used to analyse journal transient motion. Plane strain hypothesis is found to be a proper substitute for a full deformation model when a compliant liner is thinner than 2 mm (for the bearing geometry used in this study). It was also shown that the liner viscoelasticity should be taken into account whenever a compliant liner is relatively thick (in our case, 2 mm). Viscoelasticity of the liner decreases journal amplitude compared to a pure elastic liner.

  • 2. Karpov, Oleksii
    et al.
    Nosko, Pavlo
    Fil, Pavlo
    Nosko, Oleksii
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Prevention of resonance oscillations in gear mechanisms using non-circular gears2017In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 114, p. 1-10Article in journal (Refereed)
    Abstract [en]

    One of the main disadvantages of gear mechanisms is the occurrence of noise and vibrations. This study investigated the applicability of non-circular gears for preventing resonance oscillations in gear mechanisms. The influence of a small deviation of the gear centrodes from the nominal circles on kinematic and oscillatory characteristics was analysed. It was shown that a larger deviation results in a smaller resonance amplitude due to mesh frequency variability and simultaneously in higher additional dynamic loads on the mechanism. The shape of the gear centrodes was determined which provides a relatively small resonance amplitude with minimum additional dynamic loads. A mechanical device was developed to enable cutting of slightly non-circular gears on a hobbing machine without numerical control.

  • 3.
    Lian, Binbin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Song, Yimin
    Tianjin Univeristy.
    Wang, Xiaoli
    Song, Yimin
    Tianjin Univeristy.
    Passive and active gravity compensation of horizontally-mounted 3-RPS parallel kinematic machine2016In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999Article in journal (Refereed)
    Abstract [en]

    Taking a horizontally-mounted 3-RPS parallel kinematic machine (PKM) as an example, this paper investigates passive and active gravity compensation strategies for improving PKM precision. Herein, R, P and S denote revolute, actuated prismatic and spherical joint, respectively. Based on inverse position kinematic and force analysis, passive gravity compensation is firstly implemented by three extension springs. Geometric parameters of these springs are optimized by minimizing potential energy fluctuation within a prescribed workspace. Then deformation caused by gravity is adopted to evaluate compensation strategies. The deviations of an end reference point demonstrate that passive gravity compensation is capable of substantially balancing gravity. In order to further eliminate the effect of gravity, active gravity compensation is proposed to adjust spring displacements by several one degree-of-freedom (DoF) translational mechanisms. Deformation of the 3-RPS PKM is directly regarded as the objective function for determining the active translations. Overall, both passive and active gravity compensations are able to improve mechanism precision due to the partial and complete gravity balancing capability, respectively, which makes the 3-RPS PKM suitable for the application of rough and fine machining.

  • 4. Sun, T.
    et al.
    Lian, Binbin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300350, China.
    Stiffness and mass optimization of parallel kinematic machine2018In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 120, p. 73-88Article in journal (Refereed)
    Abstract [en]

    It has long been a challenge to carry out the optimal design of parallel kinematic machine (PKM) simultaneously considering stiffness and mass performances. This paper proposes the stiffness and mass optimization of PKM by settling performance indices, constraint conditions based on parameter uncertainty and cooperative equilibrium among performances. Firstly, instantaneous energy-based stiffness indices and mass in motion are defined as objectives. Instead of computationally expensive numerical analysis, analytical mapping models between objectives and parameters are investigated to improve optimization efficiency. Then, considering the effects of parameter uncertainty resulted from manufacturing errors during construction, constraint conditions are formulated by probabilistic method. Based on particle swarm optimization (PSO), a multi-objective optimization is implemented. A group of solutions are obtained to flag as Pareto frontier that reflects the competitive features between stiffness and mass performances. A cooperative equilibrium searching method is proposed to find out the final solution. Finally, this optimization approach is exemplified and validated by a five degree-of-freedom (DoF) PKM. Although its mass increases 17.17%, the stiffness is nearly 3 times better than before optimization.

  • 5.
    Sun, Tao
    et al.
    Tianjin University.
    Lian, Binbin
    Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin, 300072, China.
    Song, Yimin
    Tianjin Univeristy.
    Stiffness analysis of a2-DoF over-constrained RPM with an articulated traveling platform2016In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 96, p. 165-178Article in journal (Refereed)
    Abstract [en]

    Driven by the requirements of inter-satellite link antenna for tracking mechanism with two degree-of-freedom (DoF), this paper proposes a 2-DoF over-constrained rotational parallel mechanism (RPM) with an articulated traveling platform and formulates its stiffness model considering gravitational effects. The stiffness modeling is implemented by three steps: 1) Considering the over-constrained property and gravitational effects, twist/wrench mapping models of two R(RU)(2) limbs connecting the fixed base and the articulated traveling platform are obtained based upon screw theory. 2) Employing deformation superposition principle, the compliance models of two R(RU)(2) limbs in their joint spaces are formulated, of which component compliance is described by n-DoF (n <= 6) virtual springs; and 3) by applying deformation compatibility conditions and twist/wrench mapping models into the virtual work equations, the stiffness model of the 2-DoF over-constrained RPM considering gravitational effects is derived. From component, limbs to mechanism, the stiffness modeling process demonstrates their relations with clear physical meaning and unifies performances including kinematic, stiffness, accuracy and dynamics. This approach is verified by commercial FEA software. Finally the stiffness distribution and gravitational effects within prescribed workspace are discussed.

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