# Design and Simulation of Electromagnetic Linear Actuators for Jet Dispensers
## 1 Introduction  
Jet dispensers provide an efficient non-contact means of depositing fluid dots or fluid lines with high tolerances on plastic or metal substrates in a very short time. Jet dispensers are thus widely used in fields such as automobile engineering, medical device manufacturing, and electronics assembly [1; 2; 3; 4; 5; 6; 7; 8]. The jet dispenser configuration consists of two main parts, namely a jet valve and an actuator. During operation, the needle of the jet valve performs periodic up and down linear motion with a minimum stroke length of approximately 0.3 mm or above [9; 10]. As the needle moves with high speed in the downward direction in the dispensing stage, the exceptionally high local pressure produced at the nozzle seat breaks the fluid stream and jets the adhesive out of the nozzle in the form of droplets, which land on the substrate to make dots [11; 12]. As shown in Figure 1, the actuator drives the needle through a connecting mechanism. For actuators with a long stroke length, the actuator drives the connecting mechanism directly, as shown in Figure 0(a). However, if the shaft stroke of the actuator is less than the minimum stroke of the needle, a magnification mechanism consisting of a fulcrum and a lever arm is required to amplify the actuator stroke, as shownin Figure 1b [9; 10; 13]. In this case, the thrust force, \(F_{TF}\), generated by the actuator and the resistance force, \(F_{RF}\), impacting the needle are related as \(F_{TF}*a=F_{RF}*b\), where a and b are the lengths of the lever arms on either side of the fulcrum, respectively [14; 15; 16]. Piezo-stack actuators (PSAs) and magnetostrictive actuators (MSAs) generate a high thrust force but have a stroke length of just 100 \(\upmu\)m [17]. For most practical applications, the stroke length needs to be magnified by a factor of at least three times. Hence, the thrust force, \(F_{TF}\), increases accordingly, and energy consumption during the operation increases. Electro-pneumatic actuators (EPAs) and electromagnetic actuators (EMAs) have a smaller thrust force, but longer stroke length, than PSAs or MSAs. The displacement magnification mechanisms are not therefore required for the cases of EPAs and EMAs. The difference between EPAs and EMAs is an electromagnetic actuator used to drive the dispenser needle indirectly or directly. EPAs use a solenoid actuator to actuate open-close states of a pneumatic valve, and this valve controls the pressured air impacting the piston connected the needle to make a linear motion. Meanwhile, the EMA's shaft is connected to the dispenser needle directly, so EMAs drive the needle without intermediary linkages [14]. EMAs have many practical advantages over other types of actuators, including long actuator stroke, low required voltages, simple structure and operation, and low price. Consequently, they are widely used in many different fields nowadays, including computers, digital cameras, packaging and manufacturing, automotive, aerospace, and medicine [18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28]. Current PSA, MSA, and EPA-based jet dispensers can typically reach operating frequencies of 1000, 250, and 280 Hz, respectively [29; 30; 31]. Moreover, EMA-based jet dispensers can also achieve driving frequencies greater than 200 Hz provided that they have a stroke length of less than 0.5 mm [32; 33]. The linear EMAs have the form of solenoid actuators (SAs), moving coil/voice coil actuators (MCAs), or moving magnet actuators (MMAs). The thrust force versus stroke length characteristics of three types of EMAs is different. When operated at a short stroke length, the thrust force of MCAs and MMAs is approximately constant [34; 35], while that of SAs decreases significantly [36; 37]. Thus, the excitation current applied for SAs must be considerably increased to compensate for the thrust force drop. The literature contains many studies on the application of EMAs to jet dispensers [14; 38]. However, these studies focus only on SAs and MMAs.