Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 9(2015) No. 1

The unbalancing vibration monitoring and control of rotating machinery is an important engineering problem. In order to correct the unbalance of rotor system online, an active dynamic balancing head is designed based on the ratchet-pawl mechanism and pneumatic technology. The inner mass distribution state of balancing head can be changed to correct the unbalance when the rotor system is working in unbalancing condition. The mechanical principle and pneumatic control system of the balancing head are introduced in the paper. Based on a double-face online dynamic balancing experiment system, the balancing effect of the balancing head has been proved by many experiments. In order to improve the dynamic balancing accuracy of the balancing head in the practical application, the possible influencing factors of dynamic balancing accuracy are analyzed in the paper.

This paper presents a novel study on the analysis of the “fully compliant” spatial four-bar mechanism. To the best of our knowledge, any research on “fully compliant” spatial four-bar mechanism is not available in the literature. In the previous study performed by the authors, a “partially compliant” version of the spatial four-bar mechanism was introduced. There was a rigid spherical joint in that case, thus there was no torsional loading at flexural hinges. For the fully compliant case, there is no spherical joint in the structure of the mechanism, thereby there is also torsion available at multiple axis flexural hinges. Design of this fully compliant mechanism is different from the partially compliant case. In this study, deflections of the multiple axis flexural hinges are determined separately as bending and twist. Essential angles for manufacturing a mechanism are determined. A prototype is built and results of the mathematical model are verified with experiments. Finally, a fatigue test is performed. After one and a half million cycles it is observed that there is no indication of any failure. Since there are many applications of rigid spatial four bar mechanisms, it is strongly believed that a fully compliant version of such a mechanism may also find applications.

The crown worm drive is a new type of worm drive, it is consisting of an internal gear and a crown worm generating by the internal gear surface, and it is characterized with small size yet high-loading capacity. To satisfy the high precision requirement of crown worm tooth surface, a grinding method based on virtual center distance manufacturing principle is proposed and a grinding machine is reformed. A mathematical model was derived to calculate the theoretical probe center surface, and a measuring method is proposed to check the accuracy of crown worm tooth surface. A crown worm sample is manufactured and measured, the results show that the accuracy is 0.079mm on the upside tooth surface and 0.082mm on the underside tooth surface. The study is expected to provide the experimental foundation for the future application of the crown worm drive.

The friction of rolling guideways in the prerolling region displays hysteretic behavior known as nonlinear spring behavior (NSB). NSB deteriorates motion accuracy and causes vibration in the feed direction. Therefore, the influences of NSB on the dynamic characteristics of rolling guideways should be clarified. This paper describes the influence of NSB on the dynamic characteristics of a rolling guideway. A simple friction model is constructed based on the Masing rule. Because the proposed friction model is described with only three parameters, the factor that inherently affects the dynamic characteristics can be clearly identified. To clarify the influence of NSB, the impulse response, frequency response, and steady state motion are analyzed by numerical analysis. According to the results, the dynamic characteristics in the feed direction depend only on the change rate of friction in the prerolling region, which is introduced to the friction model as the shape factor, n. The stiffness and damping are high when the change rate of friction is high in the prerolling region. The frequency response function is force- dependent, and its tendency is varied by n. The frequency response function includes harmonic and super harmonic resonances. When the carriage is excited with a frequency lower than that of the super harmonic resonance, a displacement spike (quadrant glitch) is observed. Additionally, the nonlinearity cannot be ignored when the carriage is excited with a frequency lower than the harmonic resonance. Finally, an experiment with a roller guideway is conducted to prove the validity of the analysis. The resonance frequency and compliance at the harmonic resonance measured by the experiment accurately conform to the analytical results.

The generation principle and meshing characteristics of conjugate-curve circular arc gears, which is proposed based on the theory of conjugate curves, are studied in this paper. The generation principle and mathematical model of this gear drive are introduced according to the given spatial screw curve. Tubular meshing surfaces contacting in the orientation of designated contact angle are provided to build up circular arc tooth profiles, which inherit all properties of conjugate curves. Geometrical three-dimensional models are established based on a numerical example and the results of motion simulation show that the generated gear drive meets general meshing and motion conditions. The comparisons between this designed gear drive and conventional circular arc gearing for the generation method and meshing characteristics are carried out. And the transmission efficiency of gear pair manufactured by hobbing cutter tools is also test. Through the analysis, it shows not only the general corresponding relationship between two gears, but also the conjugate meshing essence of circular arc gears. Theoretical and experimental results demonstrate the feasibility and correctness of proposed conjugate curves theory and the application to new types of gear drive with high performance will be carried out.

We studied the effectiveness of diamond nanoparticles (DNPs) dispersed in water as a lubricant additive between stainless steel plates and sintered tungsten carbide (WC) balls. DNP dispersions with concentrations of 0.01, 0.1 and 1 wt.% were prepared and used as lubricants under a load of 1.88 N, for 240,000 friction cycles. High-friction coefficients of more than 0.3 were observed in an initial period. Then friction coefficients declined and stabilised at values of approximately 0.1. The steady-state friction coefficients were independent of the DNP concentration and lower than that for distilled water. In the initial period, wear of both the plates and ball was obvious. In the steady-state period, additional wear on the plates was a little; however, ball wear scars were clearly observed. The size of the ball wear scars decreased with decreasing the DNP concentration. It is likely that DNPs were embedded mainly in the stainless steel plates, and the embedded DNPs protected the plates and wore the balls in the steady-state period. Compared with the lubrication under distilled water, the friction coefficient and wear of the plate under the lubrication by the 0.01 wt.% DNP dispersion were lower, and the wear of the ball by this lubrication condition was not higher.