You might ask why anyone would write an article about oscillators and reciprocators in the first place? Aren't fixed guns just as effective as oscillators and reciprocators? No, not in all cases. Aren't fixed guns less costly? Yes, the initial investment is less costly. While fixed guns are quite adequate for many applications, there can be issues. I will use a flat panel as an example. On a flat panel, gun-to-gun striping, as well as unevenly distributed single-gun fan patterns can produce non-uniform film build across the part causing uneven coverage, resulting in costly rejects and rework.
Oscillators and reciprocators on the other hand provide coaters with greater control relative to lapping of fan patterns to achieve a more uniform average film build. "Lapping" or "perfect lap" is defined such that at the end of a complete cycle (one up and one down stroke), a gun spray pattern ends up right next to its initial position on the part without any overlap between the patterns, such as you will see in Figures 4 and 5 later. In other words, if configured properly as I will demonstrate, the conveyor travels the distance of E/2 (E = effective fan pattern width) during one stroke of an oscillator or reciprocator. With perfect lap, every inch of the part's surface is coated twice.