Drop-on-demand system

There are at least three types of drop-on-demand inkjet systems (47)  

An automated drop-on-demand system with real-time gravimetric control for precise dosage formulation has been developed (48). The modular drug dispensing system includes a microdispensing valve unit and is fully automated. Volumes ranging from nl to yl can be dosed with high accuracy. 

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Burgold J et al (2005) Evolution and operating experiences with different drop-on-demand systems. Macromol Rapid Commun 26(4) 265-280... 

Drop-on-demand. Drops are only triggered to fall when they are needed to print. Heinzl and Hertz discuss progress in this area by Zoltan (1972), Kyser and Sears (1976), and Stemme and Larsson (1973), pointing out how the stability and self-cleaning feature of this system considerably aided progress for drop-on-demand systems. 

One t) e of drop-on-demand system is a piezoelectric device that has as its major components an ink-fitled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. 

Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-de-mand system are an ink-filled channel having a nozzle on one end and a heat generating resistor near the nozzle. 

Nonimpact Printing. Interest is growing ia the use of nonimpact styles because of the quickness of color changeover and the abiUty to iaterface these machines to computer-aided design systems. Two basic types exist drop on demand and constant drop techniques. 

In many processes (such as oil recovery, blood flow, underground water), one encounters liquid flow through thin (micrometer diameter), noncircular-shaped tubes, or pores. In the literature, one finds studies that address these latter systems. In another context of liquid drop formation, for example, in an inkjet nozzle, this technique falls under a class of scientifically challenging technology. The inkjet printer demands such quality that this branch of drop-on-demand technology is much in the realm of industrial research. All combustion engines are controlled by oil drop formation and evaporation characteristics. The important role of capillary forces is obvious in such systems. 

The impulse or drop-on-demand ink jet is a system of fundamental simplicity. It differs from continuous ink jet systems in two aspects (1) The image-forming ink droplets are not charged, so no deflection device is involved (2) Electrical signals are only used to control the moment when an individual droplet is needed. 

Piezo drop-on-demand print head s principle of operation is relatively simple in comparison to CIJ. The jetted fluid is held in balance between a shght negative pressure in the ink system, and capillary tension in small nozzles. Each nozzle is attached to a small chamber from which ink is ejected on demand when a piezo crystal coupled to that chamber flexes on apphcation of voltage. While the principle of operation is simple, producing a viable print head is not. The print heads themselves are complex constructions and have specific requirements on the fluid to enable rehable operation. 

In the 1950s, Hansell observed the production of drops by electro-mechanically induced pressure waves [8]. In this type of system, a voltage pulse applied to a piezoelectric material that is directly or indirectly coupled to the fluid, at ambient pressure, induces a volumetric change in the fluid. This volumetric change creates pressure/velocity transients within the fluid that are directed so as to produce a drop from an orifice [9-11]. Since the voltage is applied only when the drop is needed, these types of systems are called drop-on-demand or demand mode. ... 

The drop-on-demand (DOD) system as shown schematically in Figure 11-3 is a more widely used and simpler approach for smaller drop (20-100 pm) and lower frequency (up to 20 kHz) printing applications. Figure 11-4 shows a MicroFab DOD ink-jet device generating 60-pm drop of butyl carbitol from a 50-pm orifice device at 2,000 s . ... 

In a drop-on-demand inkjet printer, the fluid is maintained at ambient pressure, and a transducer is used to create a drop only when needed. The transducer creates a volumetric change in the fluid which creates pressure waves. The pressure waves travel to an orifice and are converted to fluid velocity, which results in a drop being ejected from the orifice. Figure 8 shows a schematic of a drop-(Mi-demand-type inkjet system which can generate 60 pm diameter drops of butyl carbitol (an organic solvent) from a device with a 50 pm orifice at 4,000 drops per second. 

Fabrication of 3D Microfluidic Structures, Fig. 8 Schematic of a drop-on-demand-type inkjet system... 

Chen, L., Bao, J., Gao, C. Combinatorial synthesis of insoluble oxide library from ultrafine/ nanoparticle suspension using a drop on demand inkjet delivery system. J. Comb. Chem. 6, 699 (2004)... 

The later developed thermal inkjet technology has the advantage of being able to position a drop on demand. Ink drops are not emitted continuously but only when needed for printing. This property eliminates the need for additional systems to capture and recirculate... 

Devices employing the vaporization of superheated fluid are known concurrently as thermal ink jet or bubble jet printers, the choice of name depending on the manufacturer. Since drop on demand ink jets rely on capillary refiU, their operational frequencies are much lower than for continuous ink jet devices. This stresses the importance of the compactness of the actuating system so as to achieve reasonable printing speeds via multiple nozzle printheads. The nozzles must also be precisely registered with respect to each other if systematic print artifacts are to be avoided. 

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