Shuttering of aerosol streams
Methods and apparatuses for controlling aerosol streams being deposited onto a substrate via pneumatic shuttering. The aerosol stream is surrounded and focused by an annular co-flowing sheath gas in the print head of the apparatus. A boost gas flows to a vacuum pump during printing of the aerosol. A valve adds the boost gas to the sheath gas at the appropriate time, and a portion of the two gases is deflected in a direction opposite to the aerosol flow direction to at least partially prevent the aerosol from passing through the deposition nozzle. Some or all of the aerosol is combined with that portion of the boost gas and sheath gas and is exhausted from the print head. By precisely balancing the flows into and out of the print head, maintaining the flow rates of the aerosol and sheath gas approximately constant, and keeping the boost gas flowing during both printing and shuttering, the transition time between printing and partial or full shuttering of the aerosol stream is minimized. The pneumatic shuttering can be combined with a mechanical shutter for faster operation. A pre-sheath gas can be used to minimize the delay between the flow of gas in the center and the flow of gas near the sides of the print head flow channel.
1. A method for controlling the flow of an aerosol in a print head of an aerosol jet printing system, the method comprising:
passing an aerosol flow through the print head in an original aerosol flow direction;
surrounding the aerosol flow with a sheath gas;
passing the combined aerosol flow and the sheath gas through a deposition nozzle of the print head;
adding a boost gas to the sheath gas to form a sheath-boost gas flow;
dividing the sheath-boost gas flow into a first portion flowing in a direction opposite to the original aerosol flow direction and a second portion flowing in the original aerosol flow direction; and
the first portion of the sheath-boost gas flow preventing a deflected portion of the aerosol flow from passing through the deposition nozzle.
2. The method of claim 1 wherein a flow rate of the sheath gas and a flow rate of the aerosol flow remain approximately constant.
3. The method of claim 1 wherein prior to adding the boost gas to the sheath gas the boost gas flows to a vacuum pump.
4. The method of claim 1 further comprising extracting an exhaust flow from the print head after the dividing step, the exhaust flow comprising the deflected portion of the aerosol flow and the first portion of the sheath-boost gas flow.
5. The method of claim 4 wherein extracting the exhaust flow comprises suctioning the exhaust flow using the vacuum pump.
6. The method of claim 4 wherein a flow rate of the exhaust flow is controlled by a mass flow controller.
7. The method of claim 4 wherein a flow rate of the exhaust flow is controlled by an orifice-type flow controller or a rotameter.
8. The method of claim 1 wherein the flow rate of the sheath gas and the flow rate of the boost gas are controlled by one or more flow controllers.
9. The method of claim 8 wherein the one or more flow controllers are selected from the group consisting of mass flow controllers, orifice-type flow controllers, and rotameters.
10. The method of claim 1 wherein the flow rate of the aerosol flow prior to the adding step plus the flow rate of sheath gas prior to the adding step approximately equals a flow rate of the second portion of the sheath-boost gas flow plus a flow rate of the undeflected portion of the aerosol flow.
11. The method of claim 1 wherein the method is performed in less than approximately 10 milliseconds.
12. The method of claim 1 wherein a flow rate of the boost gas is greater than a flow rate of the aerosol flow.
13. The method of claim 12 wherein the flow rate of the boost gas is between approximately 1.2 times the flow rate of the aerosol flow and approximately 2 times the flow rate of the aerosol flow.
14. The method of claim 12 wherein the deflected portion of the aerosol flow comprises the entire aerosol flow so that none of the aerosol flow passes through the deposition nozzle.
15. The method of claim 12 wherein a flow rate of the exhaust flow is set to approximately equal the flow rate of the boost gas.
16. The method of claim 12 further comprising diverting the boost gas to flow directly to the vacuum pump prior to all of the undeflected portion of the aerosol flow exiting the print head through the deposition nozzle.
17. The method of claim 1 further comprising blocking a flow of the aerosol with a mechanical shutter prior to the preventing step.
18. The method of claim 1 wherein a flow rate of the boost gas is less than or equal to the flow rate of the aerosol flow.
19. The method of claim 18 wherein a flow rate of the exhaust flow is set to be greater than the flow rate of the boost gas.
20. The method of claim 1 further comprising surrounding the aerosol with a pre-sheath gas prior to surrounding the aerosol flow with the sheath gas.
21. The method of claim 20 wherein surrounding the aerosol flow with the sheath gas comprises the sheath gas combining with the pre-sheath gas.
22. The method of claim 20 wherein approximately half of the sheath gas is used to form the pre-sheath gas.