# Design and Experiment of a Moving Magnet Actuator Based Jetting Dispenser
## 1 Introduction  
Dispensing technology has been attracting significant attention due to its potential applications in electronics assembly [1], optoelectronics and LED [2; 3], semiconductor packaging [4], and automotive assembly [5; 6]. Dispensing technology can be used to transfer fluid materials to the desired positions accurately and rapidly when fluid materials include conductive epoxies, encapsulants, adhesives, and hydrogels [7; 8; 9]. There are two main approaches in dispensing technology: Contact and non-contact dispensing. Non-contact/jetting dispensing has several advantages and has been used for investigations and applications [10; 11; 12; 13; 14; 15; 16]. The jetting process for non-contact dispensing goes through four stages, as indicated in Figure 1. At the closing stage (Figure 0(a)), the ball-needle and nozzle-seat touch each other, and the nozzle orifice is closed. In the rising and opening stages (Figure 0(b)), the needle moves upward, and the pressurized adhesive flows from a syringe into the chamber and fills up the void generated by the nozzle-seat and ball-needle. At the end of the upward travel, the needle stops at this position for a period of time to ensure the filling process is completed. Then, the needle moves downward to punch the nozzle-seat in the dispensing stage (Figure 0(c)). The acceleration force breaks the adhesive stream. As a result, the extremely high local pressure at the area of nozzle-seat jets the adhesive out of the orifice, and then the adhesive falls down the substrate from 1-3.5 mm to form adhesive droplets. The micro-dot shapeis not affected by the shape of the needle tip and substrate surface tension because the dispenser's needle tip is not in contact with the substrate [17,18]. Currently, three types of actuators used to drive the dispenser needle have been studied. They consist of a piezo-stack actuator (PSA), a magnetostrictive-stack actuator (MSA), and an electro-pneumatic actuator (EPA). Detailed schematic diagrams of these actuators are shown in Figure 2a-d. The PSA is made of a multilayer of reformed Lead-Zirconate-Titanate (PZT) ceramics. The PZT materials generate a mechanical strain when oriented electrical charges are applied. The PSA's features include a large generated force and fast response; however, the mechanical strain is less than 100 \(\upmu\)m at a high excitation voltage of about 200 Volts. The deformation in this PSA is not great enough to directly actuate the needle displacement. Thus, an amplification mechanism including a hinge and lever is used to magnify the displacement to at least 0.35 mm [19,20]. The PSA has two major designs, in which one or two PSA blocks combined with the amplification mechanism and return spring are used, as indicated in Figure 2a,b. The MSA is made of a magneto-active material including many thin Terfenol-D plates, which generates a mechanical strain when exposed to an external magnetic field. Similar to the PSA, the elongation of the MSA is also limited by the small travel range. Thus, mechanical amplification is also used to amplify the needle displacement, as indicated in Figure 2c [11,19]. The size and cost of the PSA and MSA types also increase significantly when utilizing mechanical amplification, so they are more suitable for high-frequency applications. The EPA type uses a fast 3/2 solenoid pneumatic valve to close and open the pressured air provided by an air compressor (Figure 2d). The compressed air travels into the under cylinder chamber and pushes the piston-needle up. In the dispensing stages, the spring's compression force pushes the piston-needle down to jet the fluid out of the orifice [21, 22, 23]. The EPA has one electromagnetic valve accompanying the piston-cylinder, which raises the size of the EPA and the operating cost significantly. In addition, the pneumatic system usually incurs a pressure loss during the working process, so the pneumatic actuators have low efficiency compared with other electric-mechanical actuators.