Inkjet Jetting Simulator

The waveform is the voltage applied to the piezo wall of the ink chamber, built here from segments that each ramp to a level (% of drive voltage) over a length in µs. The ink channel behaves like a damped resonator: the simulator integrates its response to your exact waveform and draws the resulting meniscus velocity as the green curve. Every peak that crosses the ejection threshold fires a drop — one pulse gives one drop, and a multi-pulse burst gives greyscale sub-drops that merge in flight into one bigger drop. A rising edge expands the chamber and pulls the meniscus in; the fall squeezes it just as the reflected pressure wave returns, which is why a hold of about half the acoustic period is efficient. A negative brake segment after the fire cancels the leftover ringing — watch the residual % drop and the frequency-response ripple flatten.

Jettability is summarized by the Ohnesorge number: Z = 1/Oh = √(ρσd)/μ. Below Z ≈ 1 the ink is too viscous to jet cleanly; above Z ≈ 14 there is too little viscous damping and the tail breaks into satellite drops. Higher velocity stretches a longer ligament and makes satellites worse; the echo (damping) pulse cancels residual oscillation and helps both satellites and frequency ripple.

In flight, a drop leaves at 5–8 m/s and decelerates from air drag — small drops lose speed much faster, which is why light greyscale drops land less accurately. Head height (the gap from nozzle plate to media, in mm) multiplies every placement error and gives small drops more distance to slow down; too low and curl, seams or powder strike the head. Each head carries a recommended range. Placement error combines jet straightness (angle × gap) with timing error from velocity variation (carriage speed × gap × δv/v²). Tighter gap, faster drops, and slower carriage all sharpen placement. On the media, the dot spreads to roughly 1.4–2.6× the drop diameter depending on how absorbent or coated the media is.

Temperature is the second tuning knob after the waveform: warming the head thins the ink roughly exponentially (about 3%/°C), which raises drop velocity, eases refill, and lifts Z — that is why UV heads run at 40–45 °C to bring a 10–12 cP ink into the jetting window. The trade-off: hot, thin ink has less damping (satellites) and above the head's rated maximum it dries on the nozzle plate. The head heater card sets the setpoint and room temperature in °C. The ink at the nozzle settles slightly below the setpoint, takes a few time constants to get there, and can't go below room temperature because the heater only adds heat. Each head carries its own rated temperature and viscosity window, and the status bar warns when you leave it.

Ink on the film. The coating's surface tension (surface energy, in dyn/cm) against the ink's surface tension sets the contact angle: keep the coating 8–10 dyn/cm above the ink and dots wet out; below the ink they bead. Splatter comes from three places: true impact splash (rare for inkjet-sized drops, more likely with big drops on porous or fibrous surfaces), satellites, and mist. Drops leave the nozzle moving sideways with the head; still air brakes that motion, and the smallest drops lose it fastest, so satellites land behind each dot and the finest spray drifts. Higher head speed, a taller head height and smaller drops all make it worse.

Head pressure is the meniscus pressure in kPa: the ink-supply pressure at the nozzle plate, normally a slight vacuum. Surface tension can hold back about 4σ/d (a few kPa in a 20–30 µm nozzle). Pull harder than that and the meniscus is sucked into the channel and air gets in; go positive and ink weeps onto the plate. Inside the window, more vacuum retracts the meniscus a little, giving smaller, slower drops and slower refill. Aging shows up as four slow drifts — piezo drive fatigue, nozzle-plate wear that bends jets, growing shot-to-shot jitter, and permanently lost nozzles. The aging section runs the whole simulator as a head of the chosen age, so you can see exactly when placement error crosses what your work can tolerate.

Numbers are physics-based approximations (Ohnesorge/Weber scaling, channel-acoustics resonance, drag-integrated flight, published head-lifetime behavior) calibrated to typical industrial piezo heads — directionally faithful for exploring trade-offs, not a substitute for head manufacturer waveform data.