# Design and Simulation of Electromagnetic Linear Actuators for Jet Dispensers
## 3 Experimental Measuring of Necessary Thrust Force  
Before designing the SA, MCA, and MMA actuators, an experimental model of a jet valve was constructed to determine the magnitude of the necessary thrust force. In constructing the model, the design dimensions were referenced directly from previous studies in order to reduce the design time [14; 43]. The jet valve configuration is shown in Figure 4, in which the main geometric dimensions are listed in Table 1[12]. Note that the other dimensions of the valve that do not affect the flow rate or letting process of the dispensed liquid (e.g., adhesive) were simply selected in such a way as to facilitate a straightforward assembly of the jet valve parts and the subsequent integration of the jet valve with the actuator and dispenser holder. The nozzle and needle were both fabricated of S304 stainless steel, while the flange, fluid housing and nut were made of Al6061 aluminum alloy. Finally, the jet valve was fitted with commercial Misumi O-rings (NPB No. 3). Figure 4: Jet valve configuration. Figure 3: Design and analysis framework for SA, MCA, and MMA mechanisms. In the jet valve shown in Figure 4, the adhesive or other dispensed liquid is contained in a reservoir and pressurized by compressed air. During the rising stage of the needle, the pressured adhesive passes the fluid inlet port and enters the dispensing chamber. In the dispensing stage, the needle moves in the downward direction at high speed and collides with the nozzle seat. The resulting high local pressure in the nozzle-seat region causes an amount of the adhesive to be jetted out of the nozzle gate and to fall on the substrate below. The total resistance force acting on the needle as it moves in the downward direction is given by  
\[F_{TRF}=F_{FO}+F_{M}+F_{D}+F_{L} \tag{6}\]  
where \(F_{FO}\) is the friction force between the O-rings and the needle, \(F_{M}\) is the inertia force, \(F_{D}\) is the damping force of the adhesive, and \(F_{L}\) is the entire lifting force of the pressured adhesive. Figure 5 presents a photograph of the experimental setup used to measure \(F_{TRF}\). It is noted that the inertia force, \(F_{M}\), cannot be identified directly using this experimental model since the needle velocity needs to be calculated separately. Thus, \(F_{M}\) was calculated separately and then simply added to the sum of \(F_{FO}+F_{D}+F_{L}\) determined experimentally. The experimental setup was built around a ZNHBM-10 kg load sensor positioned in such a way that the sensor head contacted the tail of the jet valve needle. A Mitutoyo micrometer with a range of 0-25 mm was used to adjust the needle position to obtain a stroke length range of 0-0.5 mm. The dispensing trials were performed using glycerol with a viscosity of 950 cp of Shimakyu Chemical Co., Ltd. Moreover, the compressed air was supplied by a standalone compressor (Model: SVU(P)-203 manufactured by Tong Cheng Iron Works Co., Ltd. (Taichung, Taiwan)) and was passed through a pressure valve (Model: MAR200-8A-2K manufactured by Mindman Industrial Co., Ltd. (Taipei, Taiwan)) in order to maintain constant backpressure on the adhesive surface. An HX711 analog-to-digital converter provided by SparkFun Electronics (Colorado, United States) was used to amplify the signal received from the load sensor and then send it to an Arduino board for processing. Finally, the Arduino board was connected to a laptop to visualize the measured load data. The measurement results showed that the total resistance force acting on the needle (excluding the inertia force, i.e., \(F_{FO}+F_{D}+F_{L}\)) was equal to 3.6, 4.3, 4.8, 5.4, and 6 N for backpressures of 0, 0.5, 1, 1.5, and 2 bar, respectively.