## 1 Introduction  
In order to obtain an accurate delivery of fluid materials such as an epoxide resin or an encapsulant material, fluid dispensing systems are widely applied in many fields, including the semiconductor industry. Thus, fluid dispensing is an important process in the electronic manufacturing industry for areas such as integrated circuit (IC) chip encapsulation, surface mount technology (SMT), and light-emitting diode (LED) packaging [1; 2]. Currently, several types of dispensers have been developed and successfully applied in the field. On the basis of the delivery mode of the fluid, dispensers are classified as contact and non-contact, or jetting. With respect to contact-type dispensers, the nozzle, substrate, and dispensed fluid are simultaneously in contact with each other [3; 4; 5]. It is necessary to maintain the distance between the nozzle and the substrate to obtain good performance, and thus an accurate position control and an increased cycle time are required, and the process is complicated. In order to overcome the limitations of the contact-type dispensers, a new type of dispenser, called a jetting dispenser, was proposed and developed. With respect to the jetting-type dispensers, the fluid is ejected from the nozzle by using the kinetic energy of the needle movement [6; 7]. However, the operating frequency is generally limited to 100 Hz because the jetting dispensers are driven by conventional pneumatic and electromagnetic actuators. Furthermore, the minimum droplet size and viscosity of the fluid that is dispensed are also limited. Recently, piezoelectric jetting dispensers were proposed and developed to satisfy the market demands, including a better performance in terms of smaller size, a higher frequency, and a variety of dispensable fluids. Specifically, the dispensing heads are designed with small sizes and compact structures by adopting the structural merit intrinsic to the small sizes of the piezoelectric actuators. This means that the weight and inertia of the dispensing head are reduced, and thus a high-frequency operation is possible. The fast response time as well as the low power consumption are also important advantages of the piezoelectric jetting dispensers. [PERSON] et al. designed a jetting dispenser with two piezostack actuators and a displacement amplification device [8]. The jetting performance of a single dot was experimentally evaluated on the basis of parameters such as temperature, backpressure, and frequency. [PERSON] and [PERSON] established a dynamic model of a piezoelectric jetting dispenser and evaluated the jetting performance through a computer simulation [9]. [PERSON] et al. proposed a new type of piezoelectric jetting dispenser featuring a piezostack actuator and a cymbal-type displacement amplifier [10]. The dynamic model and governing equation were derived and the performance was evaluated through both simulation and experimentation. [PERSON] et al. also developed a bond-graph model with respect to piezoelectric jetting dispensers and verified the good performance of the proposed dispensing system [11]. [PERSON] et al. proposed various types of piezoelectric jetting dispensers and reported on the control performances of the proposed jetting systems [12; 13; 14; 15]. [PERSON] et al. proposed a new type of jetting dispenser featuring a piezostack actuator and a hydraulic displacement magnification mechanism [12; 13]. They manufactured the dispenser system and implemented the controller. The dispensing performances, including dispensing velocity and dispensed volume, were evaluated based on the applied control input. [PERSON] et al. developed a jetting dispenser configured with a piezostack actuator and a flexible beam-type displacement amplification mechanism [14]. The dispensing performance was evaluated through a computer simulation, and the verification of the results was conducted via experiments. [PERSON] and [PERSON] proposed a new type of piezoelectric jetting dispenser system actuated by dual piezostack actuators and evaluated its performance [15; 16].