Mechanism And Experimental Research On The Non-contact Jet Dispensing Valve Driven By Piezoelectric Actuator

Dispensing is assigning the glue to the workpiece surface in a certain way,so as to realize the bonding of electronic components and other functions. Especially with the rapid development of smart phones and other 3C products,the dispensing process has been more and more applied to electronic manufacturing, and the requirements of dispensing technology are also getting higher and higher. Non-contact jet dispensing can dispense in the tiny gap, which is not in contact with the workpiece and no Z axis motion. Due to the characteristics of high precision and efficiency and good dispensing consistency, it is gradually replacing the traditional contact methods.At present,Germany,the United States and other countries have mastered the technology of high precision piezoelectric jetting dispensing and commercialized it. However,our piezoelectric jetting technology started late and didn’t grasp the core technology.Therefore,we did not make it into a business.Due to the expensive price of foreign valve, the longer time for purchase, as well as the security on the part of technology and other difficulties,the piezoelectric jetting dispensing valve has been in a backward stage for us.Therefore,researching on the core technology of piezoelectric jetting dispensing valve and developing the independent intellectual property rights of our country, have the important significance.This article mainly carries on the mechanism analysis and experimental study on the jet dispensing valve driven by piezoelectric.The main contents of this paper are as follows:1、The applications introduction of piezoelectric jet valve in the dispensing process For the dispensing process, introduce the current domestic and foreign dispensing valve type used in dispensing process. Focusing on the application of piezoelectric jet dispensing valve in the dispensing process, analyze its application characteristics in the jet dispensing industry.2、The spray droplet formation model of the dispensing valve in the injection process The glue used in the dispensing process in general has high viscosity.In order to make the specified volume of glue smoothly through the injection valve,require the instantaneous pressure is large enough in chamber when the piezoelectric jet dispensing valve jet the glue.VI So establish the pressure changes mathematical model of the chamber during the process of injection. And summarize the two models of orifice flow method of chamber pressure change and Newton’s integral when the piezoelectric jetting dispensing valve inject glue.Then put forward to a similar limit mathematical model to calculate the cavity pressure of piezoelectric jetting dispensing valve. Simplify the calculation method of pressure changes in the injection process and can obtain the instantaneous pressure is positively related to diameter of the nozzle,cone angle, the impact velocity and the gas pressure.It provides the theoretical basis for controlling the injection velocity and volume of the liquid jet from the piezoelectric injection valve.3、The fluid dynamics analysis and simulation of piezoelectric jetting dispensing valve Build the model of needle hits nozzle in the injection process and use Fluent software to simulate it.Get the glue liquid pressure is positively correlated to diameter of the nozzle,cone angle,the impact velocity and the gas pressure, which is consistent with the proposed similarity limit mathematical model.Through the FLUENT software simulation of piezoelectric jetting dispensing valve can get the pressure change in an injection cycle. Also there is a negative pressure generated in the chamber when the needle is lift. When the negative pressure is large enough, the air through the nozzle orifice flow into the nozzle cavity so that the injection valve generates bubbles in the process of injection. By taking advantage of "Cambridge Trimaster" to analysis the glue drawing state at the instant of needle hits nozzle, it can get the more detailed at the gel breaking point the more likely to produce satellite drops when the piezoelectric jet dispensing valve jets glue.4、The dynamics analysis of piezoelectric jet dispensing valve Introduces the working principle of the piezoelectric jetting dispensing valve and analyzes the main structure.Firstly, the structure of the lever amplification displacement is analyzed,and the rationality of the structure is checked.By adjusting the position of the nozzle,the polished displacement of the lever can be adjusted adaptively; Then analysis the stability of needle to avoid the striker in the work process due to instability caused damage to the injection valve.Then test the motion state of the piezoelectric jetting dispensing valve.Get the output displacement of the needle under static and dynamic state when the piezoelectric stack through the lever amplification mechanism drives the motion of striker, and determine the actual displacement magnification.5、The design of the motion platform of the piezoelectric injection valve Introduce the motion platform of the piezoelectric injection valve. The working principle and driving mode of the stepping motor and servo motor are introduced respectively, as well as the working principle of the motion control card and camera and lens in visual system.Finally, the piezoelectric jetting dispensing motion platform with visual system is built.6、The experiment and test of piezoelectric jet dispensing valve Piezoelectric jet dispensing valve injection force is positively related to the velocity of needle, the diameter of needle and cone angle of nozzle through experiments.The control of a piezoelectric jet dispensing valve glue injection speed and injection volume is achieved,and it is consistent with the established mathematical model.Experiment selects piezoelectric jet dispensing valve of the needle radius of 1.6mm,the taper angle of 90° and a nozzle diameter of 0.1 mm.It can realize the viscosity of industrial 58000 cps in glue spray,and the injection plastic fluid volume is 0.71 u L.It can achieve injection of the viscosity58000 cps industrial glue,and the injection volume is 0.71 u L.