No abstract

In order to solve the problem of low precision and efficiency in the balancing process due to the movement of balance counterweights in a built-in mechanical on-line dynamic balance system, an optimization strategy for the mass compensation of the mechanical on-line dynamic balancing system is proposed, and a mass compensation optimization model is established. The optimization model takes the phase of counterweight movement as the optimization variable and the residual stress under dynamic balance as the optimization objective. Through the optimization model, the movement phase of the counterweight can be calculated, and the counterweight can be moved to a balanced position that significantly reduces the degree of unbalance. An experiment platform was built to carry out comparison experiments under different rotating speeds and unbalance levels. By comparing the residual stress, amplitude, and dynamic balancing time of the spindle before and after the balance, the accuracy of the phase of the counterweight that is calculated by the optimization model is verified. The optimized dynamic balance compensation strategy and the unoptimized were compared by experiments at different rotating speeds. The experimental results showed that, compared to the unoptimized balance, the amplitude of the spindle after optimizing balance with a dynamic balancing device can decrease by 30.39% on average, with its maximum amplitude decreasing by up 50.18%, and the balancing time can decrease by 31.72% on average, with its maximum balancing time decreasing by up to 43.86%. The research results showed that an optimization strategy can effectively improve dynamic balance efficiency and greatly reduce vibration amplitude, which provides the necessary theoretical basis for improving the running precision of the spindle system.

Unbalanced fault is the most common fault of high-speed motorized spindle, which is the main factor affecting the machining accuracy of high-speed spindle. Due to the unbalanced magnetic pull produced by the air gap eccentricity of the stator and rotor, the unbalanced vibration of the motorized spindle will be further aggravated. In order to explore the dynamic behavior and motion law of the unbalanced fault motorized spindle under the eccentric state, a dynamic model of the unbalanced fault of the high-speed motorized spindle considering the unbalanced magnetic pull was established. Taking the eccentric motorized spindle customized by the research group as the research object, the dynamic model is established, simulated, and analyzed, and the response change law of motorized spindle under the effect of different speed, unbalance, and air gap is obtained. The simulation results show that the unbalanced magnetic pull caused by static eccentricity will increase the unbalanced vibration of motorized spindle, and the unbalanced vibration will also increase with the increase of static eccentricity. The vibration caused by unbalanced magnetic pull does not increase with the increase of rotating speed. In frequency-domain analysis, when there is unbalanced magnetic pull, the peak appears at 0 Hz, and the amplitude of fundamental frequency vibration will increase with the increase of eccentricity. The experimental results show that the greater the eccentricity is, the greater the unbalance vibration of the motorized spindle is. The experimental results are consistent with the simulation results, which further verify the accuracy of the model. The research results lay a theoretical basis for fault analysis and diagnosis of coupling fault motorized spindle.

At normal operating temperatures (below 100 °C), the water in the proton exchange membrane fuel cell (PEMFC) is in the form of a mixture of gas and liquid phases. The content of water guarantees that the membrane has good proton conductivity, but it may also block the transmission of the reaction gas to the catalytic reaction sites. Based on the single straight channel of the PEMFC, the water content of the model at various voltages and the water distribution of the different parts are studied. The results indicate that the amount of water in the model generally increases with the reduction in the voltage. When the voltage is set from 1.1 V to 0.7 V, the increase in the amplitude of the water content is higher than 0.7 V–0.4 V, and the water content is highest at 0.5 V. Under each voltage, the largest water content occurs in the gas diffusion layer, the second one occurs in the channel, the third one occurs in the proton exchange membrane, and the water content in the catalyst layer is lowest.

Under high speed and high precision operation, the ceramic bearing rotor system will generate high temperature rise. Ceramic bearings and steel bearing pedestal will produce different thermal deformation due to material differences, which will lead to the non-uniform change of fit clearance. Based on the bearing heat generation and deformation mechanism, the clearance fit model of ceramic bearing rotor system is established, the contact relationship between bearing outer ring and pedestal is analyzed, and the nonlinear dynamic model of ceramic bearing rotor system considering temperature variation clearance fit is established. The nonlinear vibration characteristics of bearing rotor system under the influence of temperature variation fit clearance are investigated, and the system stability is analyzed by using phase plane diagram and bifurcation diagram. Finally, the model is verified with vibration experiments. The results show that the thermal deformation difference between the outer ring and the pedestal increases with the increase of internal temperature. The existence of temperature-varying clearance makes the amplitude of the rotor system fluctuate locally, and the vibration changes from periodic vibration to quasi-periodic motion and lengthens the chaotic period. The stability of the rotor system can be better maintained by properly reducing the bearing fit clearance at high speed. The research results lay a theoretical foundation for the further optimization design of ceramic bearing rotor system.