随着遥感卫星光学成像设备等精度的不断提升,其对振动环境的要求也在不断提高,简单的线性被动Stewart平台已经无法满足苛刻使用要求.提出了一种新型基于多边形膜片弹簧与压电致动器复合的一体化主被动Stewart减振平台,其单自由度元件主要由多边形膜片弹簧、压电致动器、力传感器以及柔性铰链组成.相较于传统线性隔振器存在的高静刚度和低动刚度之间的固有结构矛盾,所提出的多边形膜片弹簧作为隔振器的关键原件,兼具高静-低动(HSLD)特性,能够使隔振系统同时具备较高的静态刚度进行静态承载以及较低的动刚度进行动态减振.为了降低被动隔振系统中存在的共振峰幅值,本文在被动膜片弹簧元件的基础上串联一个压电致动器与力传感器组成的主动控制元件进行主动振动控制.仿真结果表明,采用比例积分力(PIF)反馈控制算法的主动控制系统,在频域上不仅可以通过积分力环节搭建出天棚阻尼的效果来降低共振峰峰值(11.19 dB),而且其比例-力环节可等效为增大了质量矩阵项,能够有效降低减振系统的固有频率(20.9 Hz),拓宽其减振带宽,并同时能维持高频段的高衰减性,在时域上也能够将系统的加速度振动幅值从±0.6g降低至±0.07g,振动衰减达88％.

With improvements in the performance of optical equipment on spacecraft, the requirements for vibration isolation have become increasingly stringent. An efficient and reliable active hybrid control (AHC) approach used for an active-passive isolation single strut (APISS) is proposed in this paper. The APISS adopts an active-passive architecture in series as one single leg of the Stewart platform. To improve performance, the AHC approach includes a modified proportional integration force (PIF) feedback control algorithm and an improved filtered-x recursive least squares (Fx-RLS) adaptive feedforward control algorithm. The PIF is applied to establish a sky-hook damping and variable mass matrix system, and Fx-RLS is employed to compensate the vibration error caused by the base platform to the payload platform. Then, a single-DOF vibration isolation system consisting of a real-time active control system and a spectrum testing and analysis system is adopted to verify the proposed approach. The experimental results indicate that the AHC approach can effectively reduce the natural frequency by 5.02 Hz. Additionally, the resonance amplitude of the natural frequency decreases by 41.84 dB, the vibration attenuation rate reaches 99.2%, and the amplitude of the mid-frequency band is further attenuated. The experimental results highlight the effectiveness of the proposed method.

In this work, the serpentine powders were sintered to make the serpentine-reinforced Al-matrix composites, and the microstructures of which were characterized by differential scanning calorimetry, thermal gravimetric analyzer, and X-ray diffractometer. Scanning electron microscopy equipped with energy dispersive spectroscopy. Results show that the sintered serpentine powders were deeply absorbed on the worn surface and embedded in the furrows and scratches of the matrix, forming a self-repairing surface layer which reduces the friction coefficient. The surface layer coated by serpentine was compact, dense, and uniform with the friction time prolonged, compensating the worn loss and increasing the matrix mass.

Purpose Serpentine is usually added into the lubricant oil to form a self-repairing protective layer on worn ferrous surface. But few works have paid close attention to the preparation of composites with the addition of serpentine. In this work, serpentine reinforced Al matrix composites were successfully prepared to be industrial lubrication components. And its fabricating parameters, compressive strength and tribological properties were analyzed. Design/methodology/approach An MM-W1 three-pin-on-disk apparatus was used to investigate the tribological properties. The worn surface, microstructure and cross-sectional morphologies were characterized by scanning electron microscopy equipped with energy dispersive spectroscopy. The compression test was carried out on a universal testing machine. An X-ray diffractometer was used to investigate the phase constitutions. The decomposition temperature of serpentine powders was investigated by a thermal analyzer, which allows simultaneous differential scanning calorimetry and thermogravimetry. With the help of finite element method model, a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. Findings Through evaluating density and Brinell hardness, sintering at 560°C for 3 h are the appropriate parameters for fabricating the composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. Originality/value Serpentine was added in fabricating the Al matrix composites for the first time. Sintering parameters were optimized to make better Al/Si/serpentine composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient under the dry sliding condition. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. It is hoped to be helpful in further confirming the factors for the formation of the self-repairing surface layer, and in designing a new industrial anti-friction composite used for dry sliding conditions.

Graphene was successfully modified by amino-functionalization process. The Fourier transform-infrared spectroscopy, Raman spectroscopy, and X-ray diffractometer were used to characterize the amino-functionalization result. The transmission electron microscopy was used to visualize the morphology of graphene and fractured surface of its resulting composite. The tribological behaviors of amino functionalized graphene reinforced polytetrafluoroethylene composite were evaluated by using a face-to-face contact mode under dry sliding/water lubricated condition. The worn surface was characterized by using a scanning electronic microscope equipped with an energy dispersive spectroscopy in order to find the reasons for the better tribological behaviors. The anti-friction and anti-wear mechanisms of amino functionalized graphene reinforced polytetrafluoroethylene composite were elucidated based on the experimental results. In all, this work is hoped to be helpful in designing and researching a new industrial material which can be used for water lubricated conditions in new-energy-vehicle fields.

Themal decomposition and poor mechanical strength of hydroxyapatite (HA) restrict its further application in the field of bone tissue engineering. A porous HA/ZrO2 gradient bioceramics with regenerated HA coating was thus designed. Its porosity reached about 70% with its compressive strength reaching about 14 MPa. The porosity and mechanical strength were balanced appropriately by immersing the bioceramics for three times using slurry concentrations of 60%, 55% and 50%, respectively. Through analyzing the decomposition and regeneration behaviour of HA by DSC, Raman and XRD, 4 mol mass of NaHCO3 heated at 900 degrees C for 2 h was the optimum condition for regenerating HA coating. The regeneration effect and process were also discussed.

Serpentine is usually added into oil for tribological applications. To explore the performance and mechanism of serpentine, three different kinds of pins were tested under lubricated/dry sliding conditions. The result shows that a surface layer with an excellent anti-friction property was formed on the surface of worn steel. The binding ability between the matrix elements in the wear-induced transition zone and the unsaturated bonds released by serpentine is the key factor to form the anti-friction surface layer. Meanwhile, the hardness of the pairing material and frictional contact time determine the thickness and surface roughness of the anti-friction surface layer. In all, this work is hoped to be helpful in designing and researching a new industrial anti-friction material which can be used for dry sliding conditions.

Purpose - This paper aims to investigate the energy-saving effect and mechanism of serpentine as lubricant additive in the simulated condition.Design/methodology/approach - An ABLT-1 bearing test machine was used for 1,350 hours and an MM-W1 three-pin-on-disk apparatus was used to investigate its anti-friction effect. The worn surface was characterized by scanning electron microscopy equipped with energy dispersive spectroscopy.Findings - The results show that the energy-saving effect was improved after adding serpentine powder in oil and that both the friction coefficient and mass loss were dramatically decreased. The analysis on worn surface layer demonstrates that an auto-reconditioning surface layer was formed on the worn surface, which was responsible for the decrease in friction and wear.Originality/value - The simulation test for the metal bearing was conducted over 1,350 hours using lubricant with and without serpentine powder. The addition of serpentine powder enhanced the energy-saving rate over time, stabilizing at about 13 per cent after 1,000 hours. An auto-reconditioning surface layer was formed on the surfaces of disassembled bearing lubricated with serpentine doped oil, resulting in dramatic decrease of both the friction coefficient and the mass loss. In addition to normal load and the accumulation of serpentine powder in the furrows and scratches of the deformed layer, the formation of the surface layer was possibly related to the substrate deformation induced by friction force.