| In the flied of industrial automation, pneumatic vacuum technology is used wildly. The vacuum ejector which based on principle of Laval nozzles is a key component in a distributed vacuum system. According to the working principle of vacuum ejector, compressed air need to be ejected directly from inlet to outlet and must be maintained for keeping a certain vacuum. The vacuum ejector has to consume large compressed air and inefficient in application. Therefore, it has great significance to research a new kind of pneumatic vacuum generator to save energy and a kind of piston vacuum generator(PVG) is emerged. Aganinst with its insufficient in vacuum response time and air consumption, the technical problem about how to meet the demands of rapid reponse and less air consumption is solved in the paper. The research of the paper is significant in pneumatic vacuum system energy saving. To achieve this goal, some interrelated technical matters are researched in this paper.Firstly, the performences of PVG principle prototype are tested. The results show that, compared with ZH10D vacuum ejector, the performances of PVG prototype is insufficient mainly in response time and air consumption. Through analysis of influence factors on main performances and for improving the system main performances, under measures are taken: few pressure loss pumping control valve, pressure balance way in vacuum cavity and two different diameters pistons. The general structure scheme of piston vacuum generator with the characteristics of rapid response and less air consumption is proposed and named as PVG-R. It established the foundation for further theoretical and experimental studies.To know dynamic response characteristics of PVG-R and the influence of main structure parameters and supply pressure on system performance, the energy equation of each cavity is deduced, and with mass flow equation and piston dynamic equation, the system mathematical model is set up and simulated. The simulation results indicate that increasing piston stroke and reducing driving chamber diameter properly would be favor to increase maximum vacuum and reduce response time, and the supply pressure should be decrease to reduce air consumption while meeting the requirement of response time.Based on these, the PVG-R prototype is designed and tested. Through the experimental research, the influence of main structure parameters and supply pressure are studied. With the flow flied simulation of pumping channel, the optimized design parameters are obtained. Experimental results show that the maximum vacuum of PVG-R prototype is about 93kPa, a little higher than ZH10D's, and the response time is about 3.70s under the condition of flow rate 50L/min. less than ZH10D's 4.80s and PVG prototype's 12.60s about 22.9% and 70.6%. Under the condition of same flow rate, response time reduction is mean to air consumption reduction.Finally, in order to save air consumption of piston vacuum generator during the course of vacuum holding, the stepped flow rate control method is proposed and realized. Based on working principle of PVG-R, the relationships of system structure parameters, working parameters and system vacuum response process are deduced theoretically. And the technocal approach which can reduce flow rate as much as during vacuum holding under the condition of keep other performances. On the base of PVG-R, the PVG-RL prototype, embedded low cost and small stepped flow rate control valve, is designed and tested. Experimental results show that, compared with ZH10D, the PVG-RL prototype can not only reach required vacuum quickly, but also save air consumption greatly. Under the same working condition, the minmaum flow rate of the PVG-RL prototype can reduce to 12L/min during the vacuum holding. It can save air consumption about 71.3% in 60s and meet the requirement of the subject. |
PDF Full Text Request