Design of a zero-force switch for use in industrial soldering guns

Trigger finger syndrome (stenosing tenosynovitis crepitans) is a repetitive trauma disorder which results in substantial costs to both industry and the industrial work force. This disease occurs when the distal phalanx of digit 2 is used repeatedly and with excessive force to operate a triggering device on a hand tool. The objective of this investigation was to design and fabricate a prototype of a soldering gun that required zero-force from the operator's trigger finger. This gun would therefore greatly reduce the pathologically degenerative condition commonly experienced with this tool. An investigation was conducted to determine the force required to operate several commercially available soldering guns. The results of this effort indicated that forces exceeding 20 N were required to operate some commercial soldering guns. Based on this information, cumulative trauma seemed possible when using these tools. A zero-force trigger was designed and placed into a commercial 100 Watt soldering gun. This design consisted of a tactile sensor that detected common-mode voltages in the operator's finger. The trigger added virtually no weight to the gun. Operation of the gun for several hundred hours has shown the design to be both robust and reliable.