Jetting device with filter status detection

A method of detecting an obstruction status of a filter in a jetting device, the jetting device comprising an ejection unit arranged to eject droplets of a liquid, the ejection unit comprising a nozzle, a liquid duct connected to the nozzle, and an electro-mechanical transducer arranged to create an acoustic pressure wave in the liquid in the duct, and the jetting device further comprising a circuit configured to measure the electric response of the transducer, said method comprising the steps of:

• ejecting droplets from the nozzle in order to create an increased demand for liquid in the duct;
• creating an acoustic pressure wave in the duct of the ejection unit by energizing the transducer with or without ejecting another droplet;
• recording changes in the electric response of the transducer that represent pressure fluctuations induced by the acoustic pressure wave in the form of a time-dependent function P(t);
• and
• judging the obstruction status of the filter on the basis of said time-dependent function P(t).

A method of detecting an obstruction status of a filter in a jetting device that comprises a plurality of ejection units, each of the plurality of ejection units being arranged to eject droplets of a liquid and comprising a nozzle, a liquid duct connected to the nozzle, and an electro-mechanical transducer arranged to create an acoustic pressure wave in the liquid in the duct, the jetting device further comprising a circuit configured to measure the electric response of the transducer, said method comprising the steps of:

• activating a number of transducers of the ejection units simultaneously for ejecting droplets from the nozzles in order to create an increased demand for liquid in the duct of at least one ejection unit, thereby creating also an acoustic pressure wave in the duct of said at least one ejection unit;
• recording changes in the electric response of the transducer that represent pressure fluctuations induced by the acoustic pressure wave in the form of a time-dependent function P(t);
• and
• judging the obstruction status of the filter on the basis of said time-dependent function P(t).

A method of detecting an obstruction status of a filter in a jetting device that comprises a plurality of ejection units, each of the plurality of ejection units being arranged to eject droplets of a liquid and comprising a nozzle, a liquid duct connected to the nozzle, and an electro-mechanical transducer arranged to create an acoustic pressure wave in the liquid in the duct, the jetting device further comprising a circuit configured to measure the electric response of the transducer, said method comprising the steps of:

• activating a number of transducers of the ejection units simultaneously for ejecting droplets from the nozzles in order to create an increased demand for liquid in the duct of at least one ejection unit;
• activating the transducer of said at least one ejection unit by another activation pulse in order to create an acoustic pressure wave in the duct of said at least one ejection unit;
• recording changes in the electric response of the transducer that represent pressure fluctuations induced by the acoustic pressure wave in the form of a time-dependent function P(t);
• and
• judging the obstruction status of the filter on the basis of said time-dependent function P(t).