Jointed pipe injector trigger mechanism

A trigger mechanism for a tubing injector for forcibly injecting or retracting a tubular string axially into or out of a well, the tubing injector comprising an upper end and a lower end, the tubular string comprising a plurality of oil field tubulars connected together with tubular connecting elements, the tubing injector comprising a plurality of gripping elements attached to at least two drive chains wherein the tubular string is disposed between the at least two drive chains, the at least two drive chains substantially parallel to each other, the plurality of gripping elements configured to make contact and apply radial force to the tubular string, the tubular connecting elements having a larger diameter than the tubulars, the tubulars comprising a tapered upset section adjacent to the tubular connecting elements, the tapered upset section comprising an upset diameter that is greater in diameter than the tubulars but less than the diameter of the tubular connecting elements, the trigger mechanism comprising:

• a) at least one trigger assembly disposed between the at least two drive chains wherein each of the at least one trigger assembly is configured to prevent the plurality of gripping elements from contacting the tubular connecting elements, wherein the at least one trigger assembly comprises:
• i) a substantially vertical frame;
• ii) a wedge disposed on the frame, wherein the wedge is disposed substantially equidistant from each of the at least two drive chains, the wedge configured to prevent the plurality of gripping elements from contacting the tapered upset section of the tubulars or the tubular connecting elements;
• and
• iii) a linear actuator configured to move the wedge in a substantially vertical direction relative to the frame wherein the wedge prevents the plurality of gripping elements from contacting the tubular connecting elements;
• and
• b) a coupling sensor configured to sense the tapered upset section and the tubular connecting elements when the tubular string is being injected into or retracted out of the well.