Methods of detecting and adjusting contact of a micro-structural fluid ejector to a substrate and method of detecting a fault condition in fluid flow from a micro-structural fluid ejector onto a substrate

A method of detecting contact of a micro-structural fluid ejector to a substrate, comprising:

• positioning the substrate on a substrate stage;
• providing a print head comprising the micro-structural fluid ejector, the micro-structural fluid ejector comprising:
• an output portion comprising an exit orifice having an output inner diameter, an input portion having an input inner diameter that is greater than the output inner diameter by a factor of at least 100, and a tapering portion between the input portion and the output portion;
• installing the print head above the substrate, the micro-structural fluid ejector being oriented with the exit orifice pointing downward;
• providing an imaging system comprising a camera, the tapering portion being located within a field-of-view of the camera;
• providing a print head positioning system which controls a vertical displacement and a lateral displacement of the print head and of the camera relative to the substrate;
• operating the imaging system to determine a current length;
• if a previous length is empty, or if the previous length is not empty but the current length is not greater than a sum of the previous length and a minimum length difference, then:
• retaining the current length as the previous length,
• lowering the print head toward the substrate by a vertical distance, and
• repeating operating the imaging system;
• and
• if the previous length is not empty and the current length is greater than the sum of the previous length and a minimum length difference, then determining that the micro-structural fluid ejector and substrate are in contact;
• wherein operating the imaging system comprises:
• capturing a digital image of the tapering portion and its surroundings;
• pre-processing the digital image to detect edges;
• and
• analyzing the digital image in a region of interest where the tapering portion and its reflection should be present to calculate the current length, the current length being defined as a length of a longest contiguous one of the detected edges intersecting a top edge of the region of interest.