As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up wi...As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed.By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence,the dimensional accuracy is improved.This work focuses on the development of this steering model.Since the method used does not increase cycle time,it is attractive for high-volume industrial applications.More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology.The results show that by activating the automated closed-loop feedback system,the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending.Since the steering model permits the direct use of additional process data,such as instant wall thickness and cross sectional distortions,it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.展开更多
Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive p...Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.展开更多
The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments.The adhesion forces between a flat tip with a diameter^1.7μm and some surface hav...The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments.The adhesion forces between a flat tip with a diameter^1.7μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope(AFM).The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces.The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface.The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy.The adhesion measurements were carried out under ambient conditions,in a nitrogen-filled glove box,under distilled water,and under potassium chloride(KCl)solution.The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area.The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization,measurement methods and the environment.Under different environments,there are different interactions and factors affecting the adhesion force,and the dominant interactions and factors may be different too.The various interactions and factors are mutually coupled to determine the final adhesion force.展开更多
文摘As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed.By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence,the dimensional accuracy is improved.This work focuses on the development of this steering model.Since the method used does not increase cycle time,it is attractive for high-volume industrial applications.More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology.The results show that by activating the automated closed-loop feedback system,the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending.Since the steering model permits the direct use of additional process data,such as instant wall thickness and cross sectional distortions,it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.
文摘Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.
基金supported by the National Natural Science Foundation of China(Grant No.51175182)
文摘The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments.The adhesion forces between a flat tip with a diameter^1.7μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope(AFM).The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces.The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface.The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy.The adhesion measurements were carried out under ambient conditions,in a nitrogen-filled glove box,under distilled water,and under potassium chloride(KCl)solution.The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area.The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization,measurement methods and the environment.Under different environments,there are different interactions and factors affecting the adhesion force,and the dominant interactions and factors may be different too.The various interactions and factors are mutually coupled to determine the final adhesion force.
