Methods and devices for automatically clearing a print head of a three-dimensional printing device

A three-dimensional (3D) printer that is configured to automatically execute a method that cleans a print head of the printer, wherein the printer comprises:

• (a) a measurement system that is configured to (i) measure an amount of printing material delivered to the print head by a propulsion system of the printer, on a per unit of time basis, and (ii) detect a disturbance in the printing material being delivered to the print head;
• and
• (b) a first drive system and a second drive system that are configured to retract the printing material, upon the measurement system detecting the disturbance in the printing material, and then re-introduce the printing material to the print head with increasing speed from zero to a pre-defined end point speed, wherein:
• (i) the measurement system is configured to be deactivated prior to the re-introducing the printing material to the print head;
• and
• (ii) the measurement system is configured to be activated after the printing material reaches a speed that is 1% to 40% of the pre-defined end point speed, whereupon the first drive system and the second drive system are configured to gradually increase the speed at which the printing material is delivered to the print head until the speed reaches 100% of the pre-defined end point speed.