Shape Memory Inkjet
Inkjet printing is an immensely useful technology. The ability to accurately place tiny drops of ink (and many other materials) and extremely high bandwidth from a parallel array of nozzles has allowed for consumer affordable high resolution printing and many other industrial applications. In most “drop-on-demand” control schemes, a thermal superheated bubble (boiling particle bearing solvent) is used to propel droplets or a piezoelectric crystal physically squeezes out droplets at high speeds. These models rely on a reservoir of material that is always “open” on one end for the droplet outlet. This makes the design of the system difficult for two reasons: the pore has to be small enough to hold back low viscosity liquids (most inks) against the downward fluid pressure by surface tension alone (~10um) and the open nozzle leaves the ink exposed and prone to drying out (forcing printers to ‘clean’ their heads every so often).
A new deposition mechanism is proposed that is based around a nozzle that is ‘plugged’ by an actuating “stopper” and a positive internal fluid pressure. When the stopper is removed, the pressure of the fluid pushes a droplet or several droplets out at high velocity until the stopper is replaced. I propose the use of nitinol wire (other materials could be used) for use as a stopper and actuator.
Full description (schematic below)
As briefly explained in the previous section, the design proposed is based off a repeatable “plugging” action of a pressure backed nozzle. The proposed technique to pull out to stopper is by thermal actuation of nitinol wire. A simple circuit would provide a brief, high current electrical impulse through the wire (or into an adjacent high resistance wire, eg. NiCr) causing a pre-stressed commercially available “muscle wire” to contract and pull from the fluid port. Cooling and subsequent return of the wire “plug” to the fluid port is of critical importance so proper thermal cooling blocks or liquids and proper reverse force biasing (either by radial pressure on the wire-via Poisson ratio expansion, roughly 0.33- or by spring tensioning the wire (with compliant spring or another nitinol wire) of the wire contraction is required for high bandwidth operation. Alternatively, instead of backing the wire plugged port with fluid pressure, the wire could be ‘cup’ shaped on the end and force a droplet out of the nozzle by the fluid pressure generated on its return path.
This nozzle ‘shutter’ or ‘plug’ actuation technique allows less dependence on the properties of the fluid being ejected (no high vapor pressure boiling fluid-like in thermal inkjets), looser manufacturing tolerance (lithography isn’t required for fabrication), and no exposure of fluid to atmosphere under non-operating conditions ) ink won’t dry out. The disadvantage of this technique is that it is unlikely that the same resolution and particle deposition rate can be achieved with this physically actuating technique (expect ~1-10 Hz maximum).
A new deposition mechanism is proposed that is based around a nozzle that is ‘plugged’ by an actuating “stopper” and a positive internal fluid pressure. When the stopper is removed, the pressure of the fluid pushes a droplet or several droplets out at high velocity until the stopper is replaced. I propose the use of nitinol wire (other materials could be used) for use as a stopper and actuator.
Full description (schematic below)
As briefly explained in the previous section, the design proposed is based off a repeatable “plugging” action of a pressure backed nozzle. The proposed technique to pull out to stopper is by thermal actuation of nitinol wire. A simple circuit would provide a brief, high current electrical impulse through the wire (or into an adjacent high resistance wire, eg. NiCr) causing a pre-stressed commercially available “muscle wire” to contract and pull from the fluid port. Cooling and subsequent return of the wire “plug” to the fluid port is of critical importance so proper thermal cooling blocks or liquids and proper reverse force biasing (either by radial pressure on the wire-via Poisson ratio expansion, roughly 0.33- or by spring tensioning the wire (with compliant spring or another nitinol wire) of the wire contraction is required for high bandwidth operation. Alternatively, instead of backing the wire plugged port with fluid pressure, the wire could be ‘cup’ shaped on the end and force a droplet out of the nozzle by the fluid pressure generated on its return path.
This nozzle ‘shutter’ or ‘plug’ actuation technique allows less dependence on the properties of the fluid being ejected (no high vapor pressure boiling fluid-like in thermal inkjets), looser manufacturing tolerance (lithography isn’t required for fabrication), and no exposure of fluid to atmosphere under non-operating conditions ) ink won’t dry out. The disadvantage of this technique is that it is unlikely that the same resolution and particle deposition rate can be achieved with this physically actuating technique (expect ~1-10 Hz maximum).
