A dispensing method and assembly for liquid droplets

摘要

A dispensing assembly for liquid droplets which comprises a dispenser (40) connected to a liquid carrying pipe (32) which in turn is connected to a source of pressurised liquid. The dispenser has an elongate body member (41) having a main bore (42) connected to the liquid carrying pipe (32). At the other end, the main bore (42) has a valve seat (43) which is connected to a nozzle (44) having a nozzle bore (45) terminating in a dispensing tip (46). A valve boss (47) of a ferromagnetic material covered with a soft polymer (48) is mounted in the main bore (42) and has a cross-sectional area less than that of the main bore (42). A separate valve boss actuating coil assembly comprising upper and lower coils (50) and (51) are provided which are separate from the main body (41) which can be unplugged from both the coils (50) and (51) and from the liquid carrying pipe (32). It is thus a disposable body member (41). In operation the valve boss is accelerated away from the initial position with the valve closed, by the coils (50) and (51) typical for a time of the order of 0.2 to 0.5 ms. The valve is then maintained open and the current in the coils are considerably reduced. The duration of this second phase determines the volume of the droplet dispensed. The second phase can be of duration of 0.1 to 5 ms, which will result in a volume of droplet dispensed in the range of 100 nl to some microlitres. Then in the third phase the valve is closed with a short pulse of high current, typically in the range of 0.2 to 0.4 ms. The fourth phase is maintaining the valve in the closed position until the next droplet has to be dispensed. There is further disclosed various electrodes to provide drop-off of any droplet on the tip (46) of the nozzle (44). Reflection electrodes are also described in conjunction with various substrates and various means for measuring the volume of droplet is also described.