## 2 Vector Printing Method Using the Encoder Sensors of Two Axes
### The Method of Using Two Encoder Signals for Vector Printing
#### 2.2.1 Development of the Encoder Processing Unit (EPU)  
We developed the so-called encoder processing unit (EPU) to generate trigger pulses at each pre-set distance in real-time, as shown in Figure 4. To generate jetting trigger signals based on two encoder signals, the EPU counts the encoder pulses from two stage axes. The maximum allowable rate of the encoder signal is 10 MHz to use the counting functions. In this study, the encoder resolution of the stage was 1 \(\upmu\)m, which means the EPU could handle the printing speed of up to 10 m/s, which is sufficient for most EHD applications. The generated trigger signals for jetting are based on position sensors and are not affected by printing speed variation, including the acceleration and deceleration parts. To change the dot spacing distance and other settings of the EPU via software, we used universal serial bus (USB) communication with personal computer (PC). For comparison with the conventional method, we prepared one trigger input BNC port (labeled as Enable) to use the external jetting trigger instead of encoder position signals, as shown in Figure 4a. In this way, two modes of \"constant distance\" using two encoder sensor signals and \"constant frequency\" using the external trigger could be selected via USB communication with the PC. To use encoder signals from two stages, a 9 D-Sub connector was used to get the position information from  
Figure 3: Non-uniform effect of vector printing on printed patterns. (**a**) Printing speed effects on dot size; (**b**) typical printed lines using a printing speed of 30 mm/s. encoders, as shown in Figure 4b. Figure 4c shows the wire pin out for the connection. Here, X and Y represent the two moving axes. Each axis has two outputs of A and B, which are 90 degrees out of phase. Table 1 shows the specifications for using the EPU. The allowed maximum drop spacing distance is 64 pulses of encoder signal. The drop spacing distance is based on the resolution of the encoders. For example, if one encoder pulse corresponds to 1 \(\upmu\)m (encoder resolution), then the drop spacing can be from 1 to 64 \(\upmu\)m. To print connected lines by using series of drops, each drop should be placed at a distance less than the drop size. For instance, if the dot size of the EHD jet on the substrate is assumed to be 5 \(\upmu\)m, the drop spacing would be set to around 3 \(\upmu\)m for connected lines using dots, which corresponds to 3 encoder pulses. The encoder resolution used in our study was 1 \(\upmu\)m, which is suitable for printing connected lines with micron sized drops. Note that, in some applications using submicron drops [9], the encoder sensors with sub-micrometer resolution should be used. In the EPU, two functions are implemented to generate an equal-spaced trigger signal: (1) an automatic trigger pulse generation function; and (2) a printing distance counting function, including non-jetting dummy distance. In the case of automatic pulse generation function, there is no limitation on the printing line length. The method usually includes acceleration and deceleration parts of staged motion to print lines. The on-off control of this mode is controlled by USB communication with the PC. However, in the case of the printing distance counting function, two additional parameters of dummy length and printing length were used to set up the starting location of printing with respect to the starting point of motion movement and printing line length, respectively. This function is developed to exclude the acceleration and deceleration regions for printing lines. Since it is based on counting the number of pulses, there is a printing line length limitation. In our implementation, the total distance from the start moving to the stop jetting should be smaller than 262,144 encoder