Inkjet Head Variables and Productivity

Written October 16, 2019

Variable Dot vs. Fixed Dot Printheads

Printhead manufacturers of piezo head units usually make two types of heads. The first type is known as a fixed drop or a head using a singular drop size. This drop size can vary, but is fixed by the manufacturer for a given head model. Larger droplets cover more area and are typically used to print lower resolution images for large applications. Billboards can be printed at resolution as low as 30dpi with no visual degradation.

Variable Drop vs. Fixed Drop

Variable drop heads, also known as Binary, or grayscale heads, have the advantage of using variable droplet sizes from the same head unit. This is accomplished by using multiple pulses or droplets that merge in flight to form a larger drop size.

The merged drop is always a multiple size of the smallest droplet that the head can produce. A head with range from 6-42pl can make drops of sizes 6, 12, 18, 24, 30, 36, and 42pl. This variable dot, when accompanied by a tuned RIP can make near photographic quality images.

Variable sizes of dots offer better gradations with low-resolution printing. Higher resolutions become even smoother in appearance. Large dots fill in large areas quickly, small dots take longer to print.

Variables that affect inkjet productivity/speed

  • Nozzles per head
  • Nozzle droplet size
    • Measured in Picoliters (One Trillionth or 10-12 liters)
    • Approx. 10 million picoliters in a drop of H20
  • Smaller drops produce higher resolutions (slower printing)
  • Large drops cover large areas faster (faster printing)
  • Variable droplets (generally slower than fixed drop size printing)
  • Firing frequency of head, specified in Khz (thoudands of drops/second)