When pulling together the technologies needed for our targeted crop spraying demonstration the mechanical engineering and fluidics presented some interesting challenges. The effect we needed was akin to that of an inkjet printer, capable of dispensing a precise volume of liquid with precise timing and direction. However, the volume and distance involved quickly ruled out using piezoelectric drop on demand technology.
Inspiration came from a much more prosaic source – a favourite kids’ toy the world over, the super soaker. A pressurised container being used to dispense liquid on demand was the perfect starting point. By varying the pressure and the valve opening time we have control over volume and velocity. Precise control over the valve was crucial, with an objective to dispense 10µL; the valve is open for just 10ms.
To the naked eye the dispense is almost invisible, in fact to capture the moment on camera we filmed at 100,000 frames per second. This gives a wonderful insight into the phenomena of droplet formation as the initial column breaks into droplets and starts to form spheres. The droplets travel over half a metre in 50ms and hit a target which is about 2cm in size that’s travelling at several metres per second. The machine vision and actuation system hits the target time after time with sniper like precision.
As impressive as these figures are you have to see it in action to appreciate how fast everything happens. You can get a flavour of the demonstration in action in our video.